ALBERT

Notes: Abstract The discovery that genes in the major histocompatibility complex (MHC) play an important role in the immune response depended on the chance interaction of several unrelated events. The first, and most important, was the decision by Michael Sela to synthesize a series of branched, multichain, synthetic polypeptides based on a backbone of poly-l-lysine. The prototype compound, (T,G)-A-L, was tipped with short random sequences of tyrosine and glutamic acid. This resulted in a restricted range of antigenic determinants composed of only two or three amino acids with a variable length-ideal for binding to the peptide binding groove of MHC class II molecules. The second was the decision by John Humphrey to immunize various strains of rabbits with this synthetic polypeptide. Two of these rabbit strains showed very large quantitative differences in antibody response to (T,G)-A-L. In transferring this system to inbred mouse strains, the third bit of good fortune was the availability at the National Institute of Medical Research, in Mill Hill (London), of the CBA (H2k) and C57 (H2b) strains. The H2b haplotype is the only one mediating a uniform high antibody response to (T,G)-A-L. The fourth critical ingredient was the availability of numerous congenic and H2 recombinant inbred strains of mice produced earlier by Snell, Stimpfling, Shreffler, and Klein. A search for congenic pairs of mice expressing the responder and nonresponder H2 haplotypes on the same background revealed that these strains responded as a function of their H2 haplotype, not of their inbred background. Extensive studies in a variety of inbred strains carrying recombinant H2 haplotypes, as well as a four-point linkage cross, mapped immune response to (T,G)A-L within the murine MHC, between the K and Ss loci. The demonstration that stimulation in the mixed lymphocyte reaction (MLR) mapped to the same region quickly led to attempts to produce antisera in congenic H2 recombinant strain combinations. These antisera identified I-region associated (Ia) antigens. Immunoprecipitation and blocking studies showed that the gene products controlling specific immune responses, the mixed lymphocyte reaction, and the structure of Ia antigens were one and the same-now designated as the I-A MHC class II molecules. These antisera and inbred strains enabled Unanue to demonstrate the peptide binding function of class II MHC molecules.

Notes: Abstract Ligation of the T cell antigen receptor (TCR) stimulates protein tyrosine kinases (PTKs), which regulate intracellular calcium and control the activity of protein kinase C (PKC) isozymes. PTKs activated by antigen receptors and costimulatory molecules also couple to phosphatidylinositol-3 kinase (PI3K) and control the activity of Ras- and Rho-family GTPases. T cell signal transduction is triggered physiologically by antigen in the context of antigen presenting cells (APC). The formation of stable and prolonged contacts between T cells and APCs is not neccessary to initiate T cell signaling but is required for effective T cell proliferation and differentiation. The stabilization of the T cell/ APC conjugate is regulated by intracellular signals induced by antigen receptors and costimulators. These coordinate the regulation of the actin and microtubule cytoskeleton and organize a specialized signaling zone that allows sustained TCR signaling.

Notes: Abstract The potential to harness the potency and specificity of the immune system underlies the growing interest in cancer immunotherapy. One such approach uses bone marrow-derived dendritic cells, phenotypically distinct and extremely potent antigen-presenting cells, to present tumor-associated antigens and thereby generate tumor-specific immunity. Support for this strategy comes from animal studies that have demonstrated that dendritic cells, when loaded ex vivo with tumor antigens and administered to tumor-bearing hosts, can elicit T cell-mediated tumor destruction. These observations have led to clinical trials designed to investigate the immunologic and clinical effects of antigen-loaded dendritic cells administered as a therapeutic vaccine to patients with cancer. In the design and conduct of such trials, important considerations include antigen selection, methods for introducing the antigen into MHC class I and II processing pathways, methods for isolating and activating dendritic cells, and route of administration. Although current dendritic cell-based vaccination methods are cumbersome, promising results from clinical trials in patients with malignant lymphoma, melanoma, and prostate cancer suggest that immunotherapeutic strategies that take advantage of the antigen presenting properties of dendritic cells may ultimately prove both efficacious and widely applicable to human tumors.

Notes: Abstract Allergic diseases affect approximately one third of the general population. This class of disease, characterized by elevated serum IgE levels and hypersensitivity to normally innocuous antigen, can manifest in practically any mucosal tissue or as a systemic response. A few examples of serious allergic diseases include asthma, dermatitis, bee sting allergy, food allergy, conjunctivitis, and severe systemic anaphylaxis. Taken together, allergic diseases constitute one of the major problems of modern day medicine. A considerable portion of the healthcare budget is expended in the treatment of allergic disease, and morbidity rates of inner city asthmatics are rising steadily. Due to the enormity of the problem, there has been a worldwide effort to identify factors that contribute to the etiology of allergic diseases. Epidemiologic studies of multigeneration families and large numbers of twins clearly indicate a strong genetic component to atopic diseases. At least two independently segregating diseasesusceptibility genes are thought to come together with environmental factors to result in allergic inflammation in a particular tissue. On the basis of the strong genetic studies, multiple groups have attempted to identify disease-susceptibility genes via either a candidate gene approach or by genome-wide scans. Both of these approaches have implicated multiple regions in the human and mouse genomes, which are currently being evaluated as harboring putative atopy genes.

Notes: Abstract The human thymus is a complex chimeric organ comprised of central (thymic epithelial space) and peripheral (perivascular space) components that functions well into adult life to produce naive T lymphocytes. Recent advances in identifying thymic emigrants and development of safe methods to study thymic function in vivo in adults have provided new opportunities to understand the role that the human thymus plays in immune reconstitution in aging, in bone marrow transplantation, and in HIV-1 infection. The emerging concept is that there are age-dependent contributions of thymic emigrants and proliferation of postthymic T cells to maintain the peripheral T cell pool and to contribute to T cell regeneration, with the thymus contributing more at younger ages and peripheral T cell expansion contributing more in older subjects. New studies have revealed a dynamic interplay between postnatal thymus output and peripheral T cell pool proliferation, which play important roles in determining the nature of immune reconstitution in congenital immunodeficiency diseases, in bone marrow transplantation, and in HIV-1 infection. In this paper, we review recent data on human postnatal thymus function that, taken together, support the notion that the human thymus is functional well into the sixth decade and plays a role throughout life to optimize human immune system function.

Notes: Abstract Antibodies can completely suppress or enhance the antibody response to their specific antigen by several hundredfold. Immunoglobulin M (IgM) enhances antibody responses via the complement system, and complement activation by IgM probably starts the chain of events leading to antibody responses to suboptimal antigen doses. IgG can enhance primary antibody responses in the absence of the complement system and seems to be dependent on Fc receptors for IgG (FcgammaRs). IgE enhances antibody responses via the low-affinity receptor for IgE (FcepsilonRII/CD23). The precise effector mechanisms that cause enhancement are not known, but direct B-cell signaling, antigen presentation, and increased follicular localization are all possibilities. IgG, IgE, and IgM may also suppress antibody responses when used in certain immunization regimes, and it seems reasonable that an important mechanism behind suppression is the masking of antigenic epitopes by antibodies. In addition, FcgammaRIIB, which contains a cytoplasmic inhibitory motif, acts as a negative regulator of antibody responses. This receptor, however, may prevent the antibody responses from exceeding a certain level rather than causing complete suppression.

Notes: Abstract Dendritic cells (DCs) are antigen-presenting cells with a unique ability to induce primary immune responses. DCs capture and transfer information from the outside world to the cells of the adaptive immune system. DCs are not only critical for the induction of primary immune responses, but may also be important for the induction of immunological tolerance, as well as for the regulation of the type of T cell-mediated immune response. Although our understanding of DC biology is still in its infancy, we are now beginning to use DC-based immunotherapy protocols to elicit immunity against cancer and infectious diseases.

Notes: Abstract The development and widespread use of vaccines against infectious agents have been a great triumph of medical science. One reason for the success of currently available vaccines is that they are capable of inducing long-lived antibody responses, which are the principal agents of immune protection against most viruses and bacteria. Despite these successes, vaccination against intracellular organisms that require cell-mediated immunity, such as the agents of tuberculosis, malaria, leishmaniasis, and human immunodeficiency virus infection, are either not available or not uniformly effective. Owing to the substantial morbidity and mortality associated with these diseases worldwide, an understanding of the mechanisms involved in generating long-lived cellular immune responses has tremendous practical importance. For these reasons, a new form of vaccination, using DNA that contains the gene for the antigen of interest, is under intensive investigation, because it can engender both humoral and cellular immune responses. This review focuses on the mechanisms by which DNA vaccines elicit immune responses. In addition, a list of potential applications in a variety of preclinical models is provided.

Notes: Abstract Physical detection of antigen-specific CD4 T cells has revealed features of the in vivo immune response that were not appreciated from in vitro studies. In vivo, antigen is initially presented to naive CD4 T cells exclusively by dendritic cells within the T cell areas of secondary lymphoid tissues. Anatomic constraints make it likely that these dendritic cells acquire the antigen at the site where it enters the body. Inflammation enhances in vivo T cell activation by stimulating dendritic cells to migrate to the T cell areas and display stable peptide-MHC complexes and costimulatory ligands. Once stimulated by a dendritic cell, antigen-specific CD4 T cells produce IL-2 but proliferate in an IL-2-independent fashion. Inflammatory signals induce chemokine receptors on activated T cells that direct their migration into the B cell areas to interact with antigen-specific B cells. Most of the activated T cells then die within the lymphoid tissues. However, in the presence of inflammation, a population of memory T cells survives. This population is composed of two functional classes. One recirculates through nonlymphoid tissues and is capable of immediate effector lymphokine production. The other recirculates through lymph nodes and quickly acquires the capacity to produce effector lymphokines if stimulated. Therefore, antigenic stimulation in the presence of inflammation produces an increased number of specific T cells capable of producing effector lymphokines throughout the body.

Notes: Abstract Rheumatoid arthritis (RA), a systemic disease, is characterized by a chronic inflammatory reaction in the synovium of joints and is associated with degeneration of cartilage and erosion of juxta-articular bone. Many pro-inflammatory cytokines including TNFalpha, chemokines, and growth factors are expressed in diseased joints. The rationale that TNFalpha played a central role in regulating these molecules, and their pathophysiological potential, was initially provided by the demonstration that anti-TNFalpha antibodies added to in vitro cultures of a representative population of cells derived from diseased joints inhibited the spontaneous production of IL-1 and other pro-inflammatory cytokines. Systemic administration of anti-TNFalpha antibody or sTNFR fusion protein to mouse models of RA was shown to be anti-inflammatory and joint protective. Clinical investigations in which the activcity of TNFalpha in RA patients was blocked with intravenously administered infliximab, a chimeric anti-TNFalpha monoclonal antibody (mAB), has provided evidence that TNF regulates IL-6, IL-8, MCP-1, and VEGF production, recruitment of immune and inflammatory cells into joints, angiogenesis, and reduction of blood levels of matrix metalloproteinases-1 and -3. Randomized, placebo-controlled, multi-center clinical trials of human TNFalpha inhibitors have demonstrated their consistent and remarkable efficacy in controlling signs and symptoms, with a favorable safety profile, in approximately two thirds of patients for up to 2 years, and their ability to retard joint damage. Infliximab (a mAB), and etanercept (a sTNF-R-Fc fusion protein) have been approved by regulatory authorities in the United States and Europe for treating RA, and they represent a significant new addition to available therapeutic options.

Notes: Abstract Natural killer cells can discriminate between normal cells and cells that do not express adequate amounts of major histocompatibility complex (MHC) class I molecules. The discovery, both in mouse and in human, of MHC-specific inhibitory receptors clarified the molecular basis of this important NK cell function. However, the triggering receptors responsible for positive NK cell stimulation remained elusive until recently. Some of these receptors have now been identified in humans, thus shedding some light on the molecular mechanisms involved in NK cell activation during the process of natural cytotoxicity. Three novel, NK-specific, triggering surface molecules (NKp46, NKp30, and NKp44) have been identified. They represent the first members of a novel emerging group of receptors collectively termed natural cytotoxicity receptors (NCR). Monoclonal antibodies (mAbs) to NCR block to differing extents the NK-mediated lysis of various tumors. Moreover, lysis of certain tumors can be virtually abrogated by the simultaneous masking of the three NCRs. There is a coordinated surface expression of the three NCRs, their surface density varying in different individuals and also in the NK cells isolated from a given individual. A direct correlation exists between the surface density of NCR and the ability of NK cells to kill various tumors. NKp46 is the only NCR involved in human NK-mediated killing of murine target cells. Accordingly, a homologue of NKp46 has been detected in mouse. Molecular cloning of NCR revealed novel members of the Ig superfamily displaying a low degree of similarity to each other and to known human molecules. NCRs are coupled to different signal transducing adaptor proteins, including CD3zeta, FcRIgamma, and KARAP/DAP12. Another triggering NK receptor is NKG2D. It appears to play either a complementary or a synergistic role with NCRs. Thus, the triggering of NK cells in the process of tumor cell lysis may often depend on the concerted action of NCR and NKG2D. In some instances, however, it may uniquely depend upon the activity of NCR or NKG2D only. Strict NKG2D-dependency can be appreciated using clones that, in spite of their NCRdull phenotype, efficiently lyse certain epithelial tumors or leukemic cell lines. Other triggering surface molecules including 2B4 and the novel NKp80 appear to function as coreceptors rather than as true receptors. Indeed, they can induce natural cytotoxicity only when co-engaged with a triggering receptor. While an altered expression or function of NCR or NKG2D is being explored as a possible cause of immunological disorders, 2B4 dysfunction has already been associated with a severe form of immunodeficiency. Indeed, in patients with the X-linked lymphoproliferative disease, the inability to control Epstein-Barr virus infections may be consequent to a major dysfunction of 2B4 that exerts inhibitory instead of activating functions.

Notes: Abstract Elevation of intracellular free Ca2+ is one of the key triggering signals for T-cell activation by antigen. A remarkable variety of Ca2+ signals in T cells, ranging from infrequent spikes to sustained oscillations and plateaus, derives from the interactions of multiple Ca2+ sources and sinks in the cell. Following engagement of the T cell receptor, intracellular channels (IP3 and ryanodine receptors) release Ca2+ from intracellular stores, and by depleting the stores trigger prolonged Ca2+ influx through store-operated Ca2+ (CRAC) channels in the plasma membrane. The amplitude and dynamics of the Ca2+ signal are shaped by several mechanisms, including K+ channels and membrane potential, slow modulation of the plasma membrane Ca2+-ATPase, and mitochondria that buffer Ca2+ and prevent the inactivation of CRAC channels. Ca2+ signals have a number of downstream targets occurring on multiple time scales. At short times, Ca2+ signals help to stabilize contacts between T cells and antigen-presenting cells through changes in motility and cytoskeletal reorganization. Over periods of minutes to hours, the amplitude, duration, and kinetic signature of Ca2+ signals increase the efficiency and specificity of gene activation events. The complexity of Ca2+ signals contains a wealth of information that may help to instruct lymphocytes to choose between alternate fates in response to antigenic stimulation.

Notes: Abstract B cell development is a highly regulated process whereby functional peripheral subsets are produced from hematopoietic stem cells, in the fetal liver before birth and in the bone marrow afterward. Here we review progress in understanding some aspects of this process in the mouse bone marrow, focusing on delineation of the earliest stages of commitment, on pre-B cell receptor selection, and B cell tolerance during the immature-to-mature B cell transition. Then we note some of the distinctions in hematopoiesis and pre-B selection between fetal liver and adult bone marrow, drawing a connection from fetal development to B-1/CD5+ B cells. Finally, focusing on CD5+ cells, we consider the forces that influence the generation and maintenance of this distinctive peripheral B cell population, enriched for natural autoreactive specificities that are encoded by particular germline VH-VL combinations.

Notes: In this essay, I make four points about the operation of the immune system. First, thanks to the innate immune system's regulation of the main costimulatory molecules CD80 and CD86, the immune system rarely mistakes a pathogen for a self-antigen. Second, the adaptive immune system consisting of T lymphocytes and B lymphocytes can mistake self for non-self because adaptive immunity is selected in single somatic cells. Third, the adaptive immune system of T lymphocytes and B lymphocytes is always referential to self, as it is selected on self-ligands; it persists in the periphery on self-ligands; and at least for T cells, it is dependent on self-ligands to be able to mount a response. Fourth, it is becoming clear that regulatory or suppressor T cells are our main defense against autoimmunity, as my first boss, Richard Gershon, had predicted. These cells recognize antigen as do all T cells, but they secrete the immunoregulatory cytokines IL-10 and TGFbeta.

Notes: Abstract A reciprocal regulation exists between the central nervous and immune systems through which the CNS signals the immune system via hormonal and neuronal pathways and the immune system signals the CNS through cytokines. The primary hormonal pathway by which the CNS regulates the immune system is the hypothalamic-pituitary-adrenal axis, through the hormones of the neuroendocrine stress response. The sympathetic nervous system regulates the function of the immune system primarily via adrenergic neurotransmitters released through neuronal routes. Neuroendocrine regulation of immune function is essential for survival during stress or infection and to modulate immune responses in inflammatory disease. Glucocorticoids are the main effector end point of this neuroendocrine system and, through the glucocorticoid receptor, have multiple effects on immune cells and molecules. This review focuses on the regulation of the immune response via the neuroendocrine system. Particular details are presented on the effects of interruptions of this regulatory loop at multiple levels in predisposition and expression of immune diseases and on mechanisms of glucocorticoid effects on immune cells and molecules.

Notes: Abstract KIR genes have evolved in primates to generate a diverse family of receptors with unique structures that enable them to recognize MHC-class I molecules with locus and allele-specificity. Their combinatorial expression creates a repertoire of NK cells that surveys the expression of almost every MHC molecule independently, thus antagonizing the spread of pathogens and tumors that subvert innate and adaptive defense by selectively downregulating certain MHC class I molecules. The genes encoding KIR that recognize classical MHC molecules have diversified rapidly in human and primates; this contrasts with conservation of immunoglobulin- and lectin-like receptors for nonclassical MHC molecules. As a result of the variable KIR-gene content in the genome and the polymorphism of the HLA system, dissimilar numbers and qualities of KIR:HLA pairs function in different humans. This diversity likely contributes variability to the function of NK cells and T-lymphocytes by modulating innate and adaptive immune responses to specific challenges.

Notes: Abstract Engagement of the T cell antigen receptor (TCR) leads to a complex series of molecular changes at the plasma membrane, in the cytoplasm, and at the nucleus that lead ultimately to T cell effector function. Activation at the TCR of a set of protein tyrosine kinases (PTKs) is an early event in this process. This chapter reviews some of the critical substrates of these PTKs, the adapter proteins that, following phosphorylation on tyrosine residues, serve as binding sites for many of the critical effector enzymes and other adapter proteins required for T cell activation. The role of these adapters in binding various proteins, the interaction of adapters with plasma membrane microdomains, and the function of adapter proteins in control of the cytoskeleton are discussed.

Notes: Abstract Typical immune responses lead to prominent clonal expansion of antigen-specific T and B cells followed by differentiation into effector cells. Most effector cells die at the end of the immune response but some of these cells survive and form long-lived memory cells. The factors controlling the formation and survival of memory T cells are reviewed.

Notes: Abstract Unmethylated CpG motifs are prevalent in bacterial but not vertebrate genomic DNAs. Oligodeoxynucleotides (ODN) containing CpG motifs activate host defense mechanisms leading to innate and acquired immune responses. The recognition of CpG motifs requires Toll-like receptor (TLR) 9, which triggers alterations in cellular redox balance and the induction of cell signaling pathways including the mitogen activated protein kinases (MAPKs) and NFkappaB. Cells that express TLR-9, which include plasmacytoid dendritic cells (PDCs) and B cells, produce Th1-like proinflammatory cytokines, interferons, and chemokines. Certain CpG motifs (CpG-A) are especially potent at activating NK cells and inducing IFN-alpha production by PDCs, while other motifs (CpG-B) are especially potent B cell activators. CpG-induced activation of innate immunity protects against lethal challenge with a wide variety of pathogens, and has therapeutic activity in murine models of cancer and allergy. CpG ODN also enhance the development of acquired immune responses for prophylactic and therapeutic vaccination.

Notes: Abstract CD8 T cells respond to viral infections but also participate in defense against bacterial and protozoal infections. In the last few years, as new methods to accurately quantify and characterize pathogen-specific CD8 T cells have become available, our understanding of in vivo T cell responses has increased dramatically. Pathogen-specific T cells, once thought to be quite rare following infection, are now known to be present at very high frequencies, particularly in peripheral, nonlymphoid tissues. With the ability to visualize in vivo CD8 T cell responses has come the recognition that T cell expansion is programmed and, to a great extent, independent of antigen concentrations. Comparison of CD8 T cell responses to different pathogens also highlights the intricate relationship between microbially induced innate inflammatory responses and the kinetics, magnitude, and character of long-term T cell responses. This review describes recent progress in some of the major murine models of CD8 T cell-mediated immunity to viral, bacterial, and protozoal infection.

Notes: Abstract A functional immune system requires the selection of T lymphocytes expressing receptors that are major histocompatibility complex restricted but tolerant to self-antigens. This selection occurs predominantly in the thymus, where lymphocyte precursors first assemble a surface receptor. In this review we summarize the current state of the field regarding the natural ligands and molecular factors required for positive and negative selection and discuss a model for how these disparate outcomes can be signaled via the same receptor. We also discuss emerging data on the selection of regulatory T cells. Such cells require a high-affinity interaction with self-antigens, yet differentiate into regulatory cells instead of being eliminated.

Notes: Abstract In the absence of antiretroviral treatment, HIV-1 establishes a chronic, progressive infection of the human immune system that invariably, over the course of years, leads to its destruction and fatal immunodeficiency. Paradoxically, while viral replication is extensive throughout the course of infection, deterioration of conventional measures of immunity is slow, including the characteristic loss of CD4+ T cells that is thought to play a key role in the development of immunodeficiency. This conundrum suggests that CD4+ T cell-directed viral cytopathicity alone cannot explain the course of disease. Indeed, recent advances now indicate that HIV-1 pathogenesis is likely to result from a complex interplay between the virus and the immune system, particularly the mechanisms responsible for T cell homeostasis and regeneration. We review these data and present a model of HIV-1 pathogenesis in which the protracted loss of CD4+ T cells results from early viral destruction of selected memory T cell populations, followed by a combination of profound increases in overall memory T cell turnover, damage to the thymus and other lymphoid tissues, and physiological limitations in peripheral CD4+ T cell renewal.

Notes: Abstract IL-13 was first recognized for its effects on B cells and monocytes, where it upregulated class II expression, promoted IgE class switching and inhibited inflammatory cytokine production. It was also thought to be functionally redundant with IL-4. However, studies conducted with knockout mice, neutralizing antibodies, and novel antagonists demonstrate that IL-13 possesses several unique effector functions that distinguish it from IL-4. Resistance to most gastrointestinal nematodes is mediated by type-2 cytokine responses, in which IL-13 plays a dominant role. By regulating cell-mediated immunity, IL-13 modulates resistance to intracellular organisms including Leishmania major, Leishmania mexicana, and Listeria monocytogenes. In the lung, IL-13 is the central mediator of allergic asthma, where it regulates eosinophilic inflammation, mucus secretion, and airway hyperresponsiveness. Manipulation of IL-13 effector function may also prove useful in the treatment of some cancers like B-cell chronic lymphocytic leukemia and Hodgkin's disease, where IL-13 modulates apoptosis or tumor cell growth. IL-13 can also inhibit tumor immunosurveillance. As such, inhibitors of IL-13 might be effective as cancer immunotherapeutics by boosting type-1-associated anti-tumor defenses. Finally, IL-13 was revealed as a potent mediator of tissue fibrosis in both schistosomiasis and asthma, which indicates that it is a key regulator of the extracellular matrix. The mechanisms that regulate IL-13 production and/or function have also been investigated, and IL-4, IL-12, IL-18, IFN-gamma, IL-10, TGF-beta, TNF-alpha, and the IL-4/IL-13 receptor complex play important roles. This review highlights the effector functions of IL-13 and describes multiple pathways for modulating its activity in vivo.

Notes: Abstract Collectins and ficolins, present in plasma and on mucosal surfaces, are humoral molecules of the innate immune systems, which recognize pathogen-associated molecular patterns. The human collectins, mannan-binding lectin (MBL) and surfactant protein A and D (SP-A and SP-D), are oligomeric proteins composed of carbohydrate-recognition domains (CRDs) attached to collagenous regions and are thus structurally similar to the ficolins, L-ficolin, M-ficolin, and H-ficolin. However, they make use of different CRD structures: C-type lectin domains for the collectins and fibrinogen-like domains for the ficolins. Upon recognition of the infectious agent, MBL and the ficolins initiate the lectin pathway of complement activation through attached serine proteases (MASPs), whereas SP-A and SP-D rely on other effector mechanisms: direct opsonization, neutralization, and agglutination. This limits the infection and concurrently orchestrates the subsequent adaptive immune response. Deficiencies of the proteins may predispose to infections or other complications, e.g., reperfusion injuries or autoimmune diseases. Structure, function, clinical implications, and phylogeny are reviewed.

Notes: Abstract The T helper lymphocyte is responsible for orchestrating the appropriate immune response to a wide variety of pathogens. The recognition of the polarized T helper cell subsets Th1 and Th2 has led to an understanding of the role of these cells in coordinating a variety of immune responses, both in responses to pathogens and in autoimmune and allergic disease. Here, we discuss the mechanisms that control lineage commitment to the Th1 phenotype. What has recently emerged is a rich understanding of the cytokines, receptors, signal transduction pathways, and transcription factors involved in Th1 differentiation. Although the picture is still incomplete, the basic pathways leading to Th1 differentiation can now be understood in in vitro and a number of infection and disease models.

Notes: Abstract Dendritic cells (DCs) have several functions in innate and adaptive immunity. In addition, there is increasing evidence that DCs in situ induce antigen-specific unresponsiveness or tolerance in central lymphoid organs and in the periphery. In the thymus DCs generate tolerance by deleting self-reactive T cells. In peripheral lymphoid organs DCs also induce tolerance to antigens captured by receptors that mediate efficient uptake of proteins and dying cells. Uptake by these receptors leads to the constitutive presentation of antigens on major histocompatibility complex (MHC) class I and II products. In the steady state the targeting of DC antigen capture receptors with low doses of antigens leads to deletion of the corresponding T cells and unresponsiveness to antigenic rechallenge with strong adjuvants. In contrast, if a stimulus for DC maturation is coadministered with the antigen, the mice develop immunity, including interferon-gamma-secreting effector T cells and memory T cells. There is also new evidence that DCs can contribute to the expansion and differentiation of T cells that regulate or suppress other immune T cells. One possibility is that distinct developmental stages and subsets of DCs and T cells can account for the different pathways to peripheral tolerance, such as deletion or suppression. We suggest that several clinical situations, including autoimmunity and certain infectious diseases, can be influenced by the antigen-specific tolerogenic role of DCs.

Notes: Abstract B cell chronic lymphocytic leukemia (B-CLL) is an accumulative disease of slowly proliferating CD5+ B lymphocytes that develops in the aging population. Whereas some patients with B-CLL have an indolent course and die after many years from unrelated causes, others progress very rapidly and succumb within a few years from this currently incurable leukemia. Over the past decade studies of the structure and function of the B cell antigen receptor (BCR) used by these leukemic cells have helped redefine the nature of this disease. In this review we summarize and reinterpret several aspects of these BCR-related studies and how they might relate to the disease. In particular, we address the ability of antigens to select out and drive B cell clones from the normal state to overt leukemic cells by binding to BCRs that are relatively unique and characteristic of B-CLL cells. The differential capacity of some B-CLL cases to continue to transduce signals through the BCR during the leukemic phase and the consequences for the in vivo biology of the leukemic clone is also considered. Finally, we discuss current and emerging views of the cellular origin of B-CLL cells and the differentiation pathways down which we believe these cells progress.

Notes: This review summarizes the major features of CD1 genes and proteins, the patterns of intracellular trafficking of CD1 molecules, and how they sample different intracellular compartments for self- and foreign lipids. We describe how lipid antigens bind to CD1 molecules with their alkyl chains buried in hydrophobic pockets and expose their polar lipid headgroup whose fine structure is recognized by the TCR of CD1-restricted T cells. CD1-restricted T cells carry out effector, helper, and adjuvant-like functions and interact with other cell types including macrophages, dendritic cells, NK cells, T cells, and B cells, thereby contributing to both innate and adaptive immune responses. Insights gained from mice and humans now delineate the extensive range of diseases in which CD1-restricted T cells play important roles and reveal differences in the role of CD1a, CD1b, and CD1c in contrast to CD1d. Invariant TCRalpha chains, self-lipid reactivity, and rapid effector responses empower a subset of CD1d-restricted T cells (NKT cells) to have unique effector functions without counterpart among MHC-restricted T cells. This review describes the function of CD1-restricted T cells in antimicrobial responses, antitumor immunity, and in regulating the balance between tolerance and autoimmunity.

Notes: After a century of controversy, the notion that the immune system regulates cancer development is experiencing a new resurgence. An overwhelming amount of data from animal models-together with compelling data from human patients-indicate that a functional cancer immunosurveillance process indeed exists that acts as an extrinsic tumor suppressor. However, it has also become clear that the immune system can facilitate tumor progression, at least in part, by sculpting the immunogenic phenotype of tumors as they develop. The recognition that immunity plays a dual role in the complex interactions between tumors and the host prompted a refinement of the cancer immunosurveillance hypothesis into one termed "cancer immunoediting." In this review, we summarize the history of the cancer immunosurveillance controversy and discuss its resolution and evolution into the three Es of cancer immunoediting-elimination, equilibrium, and escape.

Notes: Development of the acquired immune response is dependent on the signaling of CD40 by its ligand, CD154. These molecules govern both the magnitude and quality of humoral- and cell-mediated immunity. A litany of studies have conclusively documented that blockade of this ligand-receptor pair can prevent, and also intervene in, the progression of antibody- and cell-mediated autoimmune diseases, and can instill long-lived allogeneic and xenogeneic graft tolerance. Many effector mechanisms of inflammation are abolished as a result of CD154 blockade, but we are now beginning to understand that CD154 blockade may, in some instances, engender long-lived, antigen-specific tolerance. In the context of transplantation tolerance, we present a hypothesis that alphaCD154 blockade is most effective at inducing long-lived allospecific tolerance if anergy and regulation can be elicited prior to the onslaught of inflammation that is induced by grafting (preemptive tolerance). This facet of alphaCD154-induced tolerance appears to co-opt the normal processes of peripheral tolerance induced by immature DCs and can be exploited to induce long-lived antigen-specific tolerance. The underlying science and the prospects for inducing long-lived antigen-specific tolerance in a model of allograft tolerance through CD154 blockade are presented and discussed.

Notes: Understanding the molecular basis of lymphocyte homing to lymphoid organs was originally a problem of concern only to immunologists. With the discovery of l-selectin and its ligands, interested scientists have expanded to include glycobiologists, immunopathologists, cancer biologists, and developmental biologists. Going beyond its first discovered role in homing to lymph nodes, the l-selectin system is implicated in such diverse processes as inflammatory leukocyte trafficking in both acute and chronic settings, hematogenous metastasis of carcinoma cells, effector mechanisms for inflammatory demyelination of axons, and implantation of the early mammalian embryo. This review focuses on the ligands for l-selectin that are found on vascular endothelium, leukocytes, carcinoma cells, and at various extravascular sites. The discovery of selectins and their ligands has validated the long-predicted hypothesis that carbohydrate-directed cell adhesion is relevant in eukaryotic systems. Emphasis will be given to the carbohydrate and sulfation modifications of the ligands, which enable recognition by l-selectin. The rapid "homing" of labeled cells into the lymph nodes presumably had its basis in the special affinity of small lymphocytes for the endothelium of the postcapillary venules. Gowans & Knight (1)

Notes: The Class 2 alpha-helical cytokines consist of interleukin-10 (IL-10), IL-19, IL-20, IL-22, IL-24 (Mda-7), and IL-26, interferons (IFN-alpha, -beta, -e, -kappa, -omega, -delta, -tau, and -gamma) and interferon-like molecules (limitin, IL-28A, IL-28B, and IL-29). The interaction of these cytokines with their specific receptor molecules initiates a broad and varied array of signals that induce cellular antiviral states, modulate inflammatory responses, inhibit or stimulate cell growth, produce or inhibit apoptosis, and affect many immune mechanisms. The information derived from crystal structures and molecular evolution has led to progress in the analysis of the molecular mechanisms initiating their biological activities. These cytokines have significant roles in a variety of pathophysiological processes as well as in regulation of the immune system. Further investigation of these critical intercellular signaling molecules will provide important information to enable these proteins to be used more extensively in therapy for a variety of diseases.

Notes: Because of the evolutionary conservation of innate mechanisms of host defense, Drosophila has emerged as an ideal animal in which to study the genetic control of immune recognition and responses. The discovery that the Toll pathway is required for defense against fungal infection in Drosophila was pivotal in studies of both mammalian and Drosophila immunity. Subsequent genetic screens in Drosophila to isolate additional mutants unable to induce humoral responses to infection have identified and ordered the function of components of two signaling cascades, the Toll and Imd pathways, that activate responses to infection. Drosophila blood cells also contribute to host defense through phagocytosis and signaling, and may carry out a form of self-nonself recognition that is independent of microbial pattern recognition. Recent work suggests that Drosophila will be a useful model for dissecting virulence mechanisms of several medically important pathogens.

Notes: Immune cell-mediated destruction of pathogens may result in excessive collateral damage to normal tissues, and the failure to control activated immune cells may cause immunopathologies. The search for physiological mechanisms that downregulate activated immune cells has revealed a critical role for extracellular adenosine and for immunosuppressive A2A adenosine receptors in protecting tissue from inflammatory damage. Tissue damage-associated deep hypoxia, hypoxia-inducible factors, and hypoxia-induced accumulation of adenosine may represent one of the most fundamental and immediate tissue-protecting mechanisms, with adenosine A2A receptors triggering "OFF" signals in activated immune cells. In these regulatory mechanisms, oxygen deprivation and extracellular adenosine accumulation serve as "reporters," while A2A adenosine receptors serve as "sensors" of excessive tissue damage. The A2A receptor-triggered generation of intracellular cAMP then inhibits activated immune cells in a delayed negative feedback manner to prevent additional tissue damage. Targeting A2A adenosine receptors may have important clinical applications.

Notes: The present review focuses on the concept that cellular and humoral immunity to the phylogenetically highly conserved antigen heat shock protein 60 (HSP60) is the initiating mechanism in the earliest stages of atherosclerosis. Subjecting arterial endothelial cells to classical atherosclerosis risk factors leads to the expression of HSP60 that then may serve as a target for pre-existent cross-reactive antimicrobial HSP60 immunity or bona fide autoimmune reactions induced by biochemically altered autologous HSP60. Endothelial cells can also bind microbial or autologous HSP60 via Toll-like receptors, providing another possibility for targetting adaptive or innate immunological effector mechanisms.

Notes: Abstract The application of rapid methods currently used for screening discovery drug candidates for metabolism and pharmacokinetic characteristics is discussed. General considerations are given for screening in this context, including the criteria for good screens, the use of counterscreens, the proper sequencing of screens, ambiguity in the interpretation of results, strategies for false positives and negatives, and the special difficulties encountered in drug metabolism and pharmacokinetic screening. Detailed descriptions of the present status of screening are provided for absorption potential, blood-brain barrier penetration, inhibition and induction of cytochrome P450, pharmacokinetics, biotransformation, and computer modeling. Although none of the systems currently employed for drug metabolism and pharmacokinetic screening can be considered truly high-throughput, several of them are rapid enough to be a practical part of the screening paradigm for modern, fast-moving discovery programs.

Notes: Abstract Tolerance to beta cell autoantigens represents a fragile equilibrium. Autoreactive T cells specific to these autoantigens are present in most normal individuals but are kept under control by a number of peripheral tolerance mechanisms, among which CD4+ CD25+ CD62L+ T cell-mediated regulation probably plays a central role. The equilibrium may be disrupted by inappropriate activation of autoantigen-specific T cells, notably following to local inflammation that enhances the expression of the various molecules contributing to antigen recognition by T cells. Even when T cell activation finally overrides regulation, stimulation of regulatory cells by CD3 antibodies may reset the control of autoimmunity. Other procedures may also lead to disease prevention. These procedures are essentially focused on Th2 cytokines, whether used systemically or produced by Th2 cells after specific stimulation by autoantigens. Protection can also be obtained by NK T cell stimulation. Administration of beta cell antigens or CD3 antibodies is now being tested in clinical trials in prediabetics and/or recently diagnosed diabetes.

Notes: Abstract Since the description of the first mouse knockout for an IgG Fc receptor seven years ago, considerable progress has been made in defining the in vivo functions of these receptors in diverse biological systems. The role of activating FcgammaRs in providing a critical link between ligands and effector cells in type II and type III inflammation is now well established and has led to a fundamental revision of the significance of these receptors in initiating cellular responses in host defense, in determining the efficacy of therapeutic antibodies, and in pathological autoimmune conditions. Considerable progress has been made in the last two years on the in vivo regulation of these responses, through the appreciation of the importance of balancing activation responses with inhibitory signaling. The inhibitory FcR functions in the maintenance of peripheral tolerance, in regulating the threshold of activation responses, and ultimately in terminating IgG mediated effector stimulation. The consequences of deleting the inhibitory arm of this system are thus manifested in both the afferent and efferent immune responses. The hyperresponsive state that results leads to greatly magnified effector responses by cytotoxic antibodies and immune complexes and can culminate in autoimmunity and autoimmune disease when modified by environmental or genetic factors. FcgammaRs offer a paradigm for the biological significance of balancing activation and inhibitory signaling in the expanding family of activation/inhibitory receptor pairs found in the immune system.

Notes: Abstract The adaptive immune response is initiated by the interaction of T cell antigen receptors with major histocompatibility complex molecule-peptide complexes in the nanometer scale gap between a T cell and an antigen-presenting cell, referred to as an immunological synapse. In this review we focus on the concept of immunological synapse formation as it relates to membrane structure, T cell polarity, signaling pathways, and the antigen-presenting cell. Membrane domains provide an organizational principle for compartmentalization within the immunological synapse. T cell polarization by chemokines increases T cell sensitivity to antigen. The current model is that signaling and formation of the immunological synapse are tightly interwoven in mature T cells. We also extend this model to natural killer cell activation, where the inhibitory NK synapse provides a striking example in which inhibition of signaling leaves the synapse in its nascent, inverted state. The APC may also play an active role in immunological synapse formation, particularly for activation of naive T cells.

Notes: Abstract A broad array of biological responses, including cell polarization, movement, immune and inflammatory responses, and prevention of HIV-1 infection, are triggered by the chemokines, a family of structurally related chemoattractant proteins that bind to specific seven-transmembrane receptors linked to G proteins. Here we discuss one of the early signaling pathways activated by chemokines, the JAK/STAT pathway. Through this pathway, and possibly in conjunction with other signaling pathways, the chemokines promote changes in cellular morphology, collectively known as polarization, required for chemotactic responses. The polarized cell expresses the chemokine receptors at the leading cell edge, to which they are conveyed by rafts, a cholesterol-enriched membrane fraction fundamental to the lateral organization of the plasma membrane. Finally, the mechanisms through which the chemokines promote their effect are discussed in the context of the prevention of HIV-1 infection.

Notes: Abstract The T cell compartment of adaptive immunity provides vertebrates with the potential to survey for and respond specifically to an incredible diversity of antigens. The T cell repertoire must be carefully regulated to prevent unwanted responses to self. In the periphery, one important level of regulation is the action of costimulatory signals in concert with T cell antigen-receptor (TCR) signals to promote full T cell activation. The past few years have revealed that costimulation is quite complex, involving an integration of activating signals and inhibitory signals from CD28 and CTLA-4 molecules, respectively, with TCR signals to determine the outcome of a T cell's encounter with antigen. Newly emerging data suggest that inhibitory signals mediated by CTLA-4 not only can determine whether T cells become activated, but also can play a role in regulating the clonal representation in a polyclonal response. This review primarily focuses on the cellular and molecular mechanisms of regulation by CTLA-4 and its manipulation as a strategy for tumor immunotherapy.

Notes: Abstract Interleukin-10 (IL-10), first recognized for its ability to inhibit activation and effector function of T cells, monocytes, and macrophages, is a multifunctional cytokine with diverse effects on most hemopoietic cell types. The principal routine function of IL-10 appears to be to limit and ultimately terminate inflammatory responses. In addition to these activities, IL-10 regulates growth and/or differentiation of B cells, NK cells, cytotoxic and helper T cells, mast cells, granulocytes, dendritic cells, keratinocytes, and endothelial cells. IL-10 plays a key role in differentiation and function of a newly appreciated type of T cell, the T regulatory cell, which may figure prominently in control of immune responses and tolerance in vivo. Uniquely among hemopoietic cytokines, IL-10 has closely related homologs in several virus genomes, which testify to its crucial role in regulating immune and inflammatory responses. This review highlights findings that have advanced our understanding of IL-10 and its receptor, as well as its in vivo function in health and disease.

Notes: Abstract MAP kinases are among the most ancient signal transduction pathways and are widely used throughout evolution in many physiological processes. In mammalian species, MAP kinases are involved in all aspects of immune responses, from the initiation phase of innate immunity, to activation of adaptive immunity, and to cell death when immune function is complete. In this review, we summarize recent progress in understanding the function and regulation of MAP kinase pathways in these phases of immune responses.

Notes: Abstract Class switch recombination (CSR) and somatic hypermutation (SHM) have been considered to be mediated by different molecular mechanisms because both target DNAs and DNA modification products are quite distinct. However, involvement of activation-induced cytidine deaminase (AID) in both CSR and SHM has revealed that the two genetic alteration mechanisms are surprisingly similar. Accumulating data led us to propose the following scenario: AID is likely to be an RNA editing enzyme that modifies an unknown pre-mRNA to generate mRNA encoding a nicking endonuclease specific to the stem-loop structure. Transcription of the S and V regions, which contain palindromic sequences, leads to transient denaturation, forming the stem-loop structure that is cleaved by the AID-regulated endonuclease. Cleaved single-strand tails will be processed by error-prone DNA polymerase-mediated gap-filling or exonuclease-mediated resection. Mismatched bases will be corrected or fixed by mismatch repair enzymes. CSR ends are then ligated by the NHEJ system while SHM nicks are repaired by another ligation system.

Notes: Abstract Virtually all of the measurable cell-mediated cytotoxicity delivered by cytotoxic T lymphocytes and natural killer cells comes from either the granule exocytosis pathway or the Fas pathway. The granule exocytosis pathway utilizes perforin to traffic the granzymes to appropriate locations in target cells, where they cleave critical substrates that initiate DNA fragmentation and apoptosis; granzymes A and B induce death via alternate, nonoverlapping pathways. The Fas/FasL system is responsible for activation-induced cell death but also plays an important role in lymphocyte-mediated killing under certain circumstances. The interplay between these two cytotoxic systems provides opportunities for therapeutic interventions to control autoimmune diseases and graft vs. host disease, but oversuppression of these pathways may also lead to increased viral susceptibility and/or decreased tumor cell killing.

Notes: Abstract Gene-chips contain thousands of nucleotide sequences that allow simultaneous analysis of the complex mixture of RNAs transcribed in cells. Like these gene-chips, major histocompatibility complex (MHC) class I molecules display a large array of peptides on the cell surface for probing by the CD8+ T cell repertoire. The peptide mixture represents fragments of most, if not all, intracellular proteins. The antigen processing machinery accomplishes the daunting task of sampling these proteins and cleaving them into the precise set of peptides displayed by MHC I molecules. It has long been believed that antigenic peptides arose as by-products of normal protein turnover. Recent evidence, however, suggests that the primary source of peptides is newly synthesized proteins that arise from conventional as well as cryptic translational reading frames. It is increasingly clear that for many peptides the C-terminus is generated in the cytoplasm, and N-terminal trimming occurs in the endoplasmic reticulum in an MHC I-dependent manner. Nature's gene-chips are thus both parsimonious and elegant.

Notes: Abstract Dendritic cells take up antigens in peripheral tissues, process them into proteolytic peptides, and load these peptides onto major histocompatibility complex (MHC) class I and II molecules. Dendritic cells then migrate to secondary lymphoid organs and become competent to present antigens to T lymphocytes, thus initiating antigen-specific immune responses, or immunological tolerance. Antigen presentation in dendritic cells is finely regulated: antigen uptake, intracellular transport and degradation, and the traffic of MHC molecules are different in dendritic cells as compared to other antigen-presenting cells. These specializations account for dendritic cells' unique role in the initiation of immune responses and the induction of tolerance.

Notes: Abstract The novel protein kinase C (PKC) isoform, PKCtheta, is selectively expressed in T lymphocytes and is a sine qua non for T cell antigen receptor (TCR)-triggered activation of mature T cells. Productive engagement of T cells by antigen-presenting cells (APCs) results in recruitment of PKCtheta to the T cell-APC contact area-the immunological synapse-where it interacts with several signaling molecules to induce activation signals essential for productive T cell activation and IL-2 production. The transcription factors NF-kappaB and AP-1 are the primary physiological targets of PKCtheta, and efficient activation of these transcription factors by PKCtheta requires integration of TCR and CD28 costimulatory signals. PKCtheta cooperates with the protein Ser/Thr phosphatase, calcineurin, in transducing signals leading to activation of JNK, NFAT, and the IL-2 gene. PKCtheta also promotes T cell cycle progression and regulates programmed T cell death. The exact mode of regulation and immediate downstream substrates of PKCtheta are still largely unknown. Identification of these molecules and determination of their mode of operation with respect to the function of PKCtheta will provide essential information on the mechanism of T cell activation. The selective expression of PKCtheta in T cells and its essential role in mature T cell activation establish it as an attractive drug target for immunosuppression in transplantation and autoimmune diseases.

Notes: Abstract TNF and TNFR family proteins play important roles in the control of cell death, proliferation, autoimmunity, the function of immune cells, or the organogenesis of lymphoid organs. Recently, novel members of this large family have been identified that have critical functions in immunity and that couple lymphoid cells with other organ systems such as bone morphogenesis and mammary gland formation in pregnancy. The TNF-family molecule RANK-L (RANK-L, TRANCE, ODF) and its receptor RANK are key regulators of bone remodeling, and they are essential for the development and activation of osteoclasts. Intriguingly, RANK-L/RANK interactions also regulate T cell/dendritic cell communications, dendritic cell survival, and lymph node formation; T cell-derived RANK-L can mediate bone loss in arthritis and periodontal disease. Moreover, RANK-L and RANK are expressed in mammary gland epithelial cells, and they control the development of a lactating mammary gland during pregnancy and the propagation of mammalian species. Modulation of these systems provides us with a unique opportunity to design novel therapeutics to inhibit bone loss in arthritis, periodontal disease, and osteoporosis.

Notes: Abstract Apoptotic cell death plays a critical role in the development and functioning of the immune system. During differentiation, apoptosis weeds out lymphocytes lacking useful antigen receptors and those expressing dangerous ones. Lymphocyte death is also involved in limiting the magnitude and duration of immune responses to infection. In this review, we describe the role of the Bcl-2 protein family, and to a lesser extent that of death receptors (members of the tumor necrosis factor receptor family with a death domain), in the control of lymphoid and myeloid cell survival. We also consider the pathogenic consequences of failure of apoptosis in the immune system.

Notes: Abstract Plasma cells are terminally differentiated final effectors of the humoral immune response. Plasma cells that result from antigen activation of B-1 and marginal zone B cells provide the first, rapid response to antigen. Plasma cells that develop after a germinal center reaction provide higher-affinity antibody and often survive many months in the bone marrow. Transcription factors Bcl-6 and Pax5, which are required for germinal center B cells, block plasmacytic differentiation and repress Blimp-1 and XBP-1, respectively. When Bcl-6-dependent repression of Blimp-1 is relieved, Blimp-1 ensures that plasmacytic development is irreversible by repressing BCL-6 and PAX5. In plasma cells, Blimp-1, XBP-1, IRF4, and other regulators cause cessation of cell cycle, decrease signaling from the B cell receptor and communication with T cells, inhibit isotype switching and somatic hypermutation, downregulate CXCR5, and induce copious immunoglobulin synthesis and secretion. Thus, commitment to plasmacytic differentiation involves inhibition of activities associated with earlier B cell developmental stages as well as expression of the plasma cell phenotype.

Notes: Abstract The innate immune system in drosophila and mammals senses the invasion of microorganisms using the family of Toll receptors, stimulation of which initiates a range of host defense mechanisms. In drosophila antimicrobial responses rely on two signaling pathways: the Toll pathway and the IMD pathway. In mammals there are at least 10 members of the Toll-like receptor (TLR) family that recognize specific components conserved among microorganisms. Activation of the TLRs leads not only to the induction of inflammatory responses but also to the development of antigen-specific adaptive immunity. The TLR-induced inflammatory response is dependent on a common signaling pathway that is mediated by the adaptor molecule MyD88. However, there is evidence for additional pathways that mediate TLR ligand-specific biological responses.

Notes: Abstract A novel lymphocyte lineage, Valpha14 natural killer T (NKT) cells, is now well established as distinct from conventional alphabeta T cells. Valpha14 NKT cells express a single invariant Valpha14 antigen receptor that is essential for their development. Successful identification of a specific ligand, alpha-galactosylceramide(alpha-GalCer), and the establishment of gene-manipulated mice with selective loss of Valpha14 NKT cells helped elucidate the remarkable functional diversity of Valpha14 NKT cells in various immune responses such as host defense by mediating anti-nonself innate immune reaction, homeostatic regulation of anti-self responses, and antitumor immunity.

Notes: Abstract The Human Genome Project transformed the quest of more than 50 years to understand the major histocompatibility complex (Mhc). The sequence of the Mhc from human and mouse, together with a large amount of sequence and mapping information from several other species, allows us to draw general conclusions about the organization and origin of this crucial part of the immune system. The Mhc is a mosaic of stretches formed by conserved and nonconserved genes. Surprisingly, of the ~3.6-Mb Mhc, the stretches that encode the class I and class II genes, which epitomize the Mhc, are the least conserved part, whereas the ~1.7-Mb stretches that encode at least 115 other genes are highly conserved. We summarize the available data to answer the questions (a) What is the Mhc? and (b) How can we define it in a general, not species-specific, way? Knowing what is essential and what is incidental helps us understand the fundamentals of the Mhc, and defining the species differences makes the model organisms more useful.

Notes: The twenty-first century is beginning with a sharp turn in the field of cancer therapy. Molecular targeted therapies against specific oncogenic events are now possible. The BCR-ABL story represents a notable example of how research from the fields of cytogenetics, retroviral oncology, protein phosphorylation, and small molecule chemical inhibitors can lead to the development of a successful molecular targeted therapy. Imatinib mesylate (Gleevec, STI571, or CP57148B) is a direct inhibitor of ABL (ABL1), ARG (ABL2), KIT, and PDGFR tyrosine kinases. This drug has had a major impact on the treatment of chronic myelogenous leukemia (CML) as well as other blood neoplasias and solid tumors with etiologies based on activation of these tyrosine kinases. Analysis of CML patients resistant to BCR-ABL suppression by Imatinib mesylate coupled with the crystallographic structure of ABL complexed to this inhibitor have shown how structural mutations in ABL can circumvent an otherwise potent anticancer drug. The successes and limitations of Imatinib mesylate hold general lessons for the development of alternative molecular targeted therapies in oncology.

Notes: The purpose of immunological memory is to protect the host from reinfection, to control persistent infections, and, through maternal antibody, to protect the host's immunologically immature offspring from primary infections. Immunological memory is an exclusive property of the acquired immune system, where in the presence of CD4 T cell help, T cells and B cells clonally expand and differentiate to provide effector systems that protect the host from pathogens. Here we describe how T and B cell memory is generated in response to virus infections and how these cells respond when the host is infected again by similar or different viruses.

Notes: Human vascular endothelial cells (EC) basally display class I and II MHC-peptide complexes on their surface and come in regular contact with circulating T cells. We propose that EC present microbial antigens to memory T cells as a mechanism of immune surveillance. Activated T cells, in turn, provide both soluble and contact-dependant signals to modulate normal EC functions, including formation and remodeling of blood vessels, regulation of blood flow, regulation of blood fluidity, maintenance of permselectivity, recruitment of inflammatory leukocytes, and antigen presentation leading to activation of T cells. T cell interactions with vascular EC are thus bidirectional and link the immune and circulatory systems.

Notes: Dendritic cells (DCs) are highly efficient antigen-presenting cells (APCs) that collect antigen in body tissues and transport them to draining lymph nodes. Antigenic peptides are loaded onto major histocompatibility complex (MHC) molecules for presentation to naive T cells, resulting in the induction of cellular and humoral immune responses. DCs take up antigen through phagocytosis, pinocytosis, and endocytosis via different groups of receptor families, such as Fc receptors for antigen-antibody complexes, C-type lectin receptors (CLRs) for glycoproteins, and pattern recognition receptors, such as Toll-like receptors (TLRs), for microbial antigens. Uptake of antigen by CLRs leads to presentation of antigens on MHC class I and II molecules. DCs are well equipped to distinguish between self- and nonself-antigens by the variable expression of cell-surface receptors such as CLRs and TLRs. In the steady state, DCs are not immunologically quiescent but use their antigen-handling capacities to maintain peripheral tolerance. DCs are continuously sampling and presenting self- and harmless environmental proteins to silence immune activation. Uptake of self-components in the intestine and airways are good examples of sites where continuous presentation of self- and foreign antigens occurs without immune activation. In contrast, efficient antigen-specific immune activation occurs upon encounter of DCs with nonself-pathogens. Recognition of pathogens by DCs triggers specific receptors such as TLRs that result in DC maturation and subsequently immune activation. Here we discuss the concept that cross talk between TLRs and CLRs, differentially expressed by subsets of DCs, accounts for the different pathways to peripheral tolerance, such as deletion and suppression, and immune activation.

Notes: Only 5 to 10% of immunocompetent humans are susceptible to tuberculosis, and over 85% of them develop the disease exclusively in the lungs. Human immunodeficiency virus (HIV)-infected humans, in contrast, can develop systemic disease that is more quickly lethal. This is in keeping with other evidence showing that susceptible humans generate some level of Th1 immunity to Mycobacterium tuberculosis (Mtb) infection. Tuberculosis in mice is also exclusively a lung disease that is progressive and lethal, in spite of the generation of Th1-mediated immunity. Thus mouse tuberculosis is a model of tuberculosis in susceptible humans, as is tuberculosis in guinea pigs and rabbits. Inability to resolve infection and prevent disease may not be a consequence of the generation of an inadequate number of Th1 cells but of an intrinsic deficiency in macrophage function that prevents these cells from expressing immunity. If this proves to be true, vaccinating susceptible humans against tuberculosis will be a difficult task.

Notes: Chemokines compose a sophisticated communication system used by all our cell types, including immune cells. Chemokine messages are decoded by specific receptors that initiate signal transduction events leading to a multitude of cellular responses, leukocyte chemotaxis and adhesion in particular. Critical determinants of the in vivo activities of chemokines in the immune system include their presentation by endothelial cells and extracellular matrix molecules, as well as their cellular uptake via "silent" chemokine receptors (interceptors) leading either to their transcytosis or to degradation. These regulatory mechanisms of chemokine histotopography, as well as the promiscuous and overlapping receptor specificities of inflammation-induced chemokines, shape innate responses to infections and tissue damage. Conversely, the specific patterns of homeostatic chemokines, where each chemokine is perceived by a single receptor, are charting lymphocyte navigation routes for immune surveillance. This review presents our current understanding of the mechanisms that regulate the cellular perception and pathophysiologic meaning of chemokines.

Notes: Mutations in nine different genes have been found to cause the human severe combined immunodeficiency syndrome. The products of three of the genes-IL-2RG, Jak3, and IL-7Ralpha-are components of cytokine receptors, and the products of three more-RAG1, RAG2, and Artemis-are essential for effecting antigen receptor gene rearrangement. Additionally, a deficiency of CD3delta, a component of the T-cell antigen receptor, results in a near absence of circulating mature CD3+ T cells and a complete lack of gamma/delta T cells. Adenosine deaminase deficiency results in toxic accumulations of metabolites that cause T cell apoptosis. Finally, a deficiency of CD45, a critical regulator of signaling thresholds in immune cells, also causes SCID. Approaches to immune reconstitution have included bone marrow transplantation and gene therapy. Bone marrow transplantation, both HLA identical unfractionated and T cell-depleted HLA haploidentical, has been very successful in effecting immune reconstitution if done in the first 3.5 months of life and without pretransplant chemotherapy. Gene therapy was highly successful in nine infants with X-linked SCID, but the trials have been placed on hold due to the development of a leukemic process in two of the children because of insertional oncogenesis.

Notes: Cells of the immune system carry out diverse functions that are controlled by surface receptors for antigen, costimulatory molecules, cytokines, chemokines, and other ligands. A shared feature of signal transduction downstream of most receptors on immune cells, as in nonhematopoietic cell types, is the activation of phosphoinositide 3-kinase (PI3K). The mechanism by which this common signaling event is elicited by distinct receptors and contributes to unique functional outcomes is an intriguing puzzle. Understanding how specificity is achieved in PI3K signaling is of particular significance because altered regulation of this pathway is observed in many disease states, including leukemia and lymphoma. Here we review recent advances in the understanding of PI3K signaling mechanisms in different immune cells and receptor systems. We emphasize the concept that PI3K and its products are components of complex networks of interacting proteins and second messengers, rather than simple links in linear signaling cascades.

Notes: The present review focuses on the concept that cellular and humoral immunity to the phylogenetically highly conserved antigen heat shock protein 60 (HSP60) is the initiating mechanism in the earliest stages of atherosclerosis. Subjecting arterial endothelial cells to classical atherosclerosis risk factors leads to the expression of HSP60 that then may serve as a target for pre-existent cross-reactive antimicrobial HSP60 immunity or bona fide autoimmune reactions induced by biochemically altered autologous HSP60. Endothelial cells can also bind microbial or autologous HSP60 via Toll-like receptors, providing another possibility for targetting adaptive or innate immunological effector mechanisms.

Notes: Abstract The vasculature of individual tissues is highly specialized. The endothelium in lymphoid tissues expresses tissue-specific receptors for lymphocyte homing, and recent work utilizing phage homing has revealed an unprecedented degree of specialization in the vasculature of other normal tissues. In vivo screening of libraries of phage that displace random peptide sequences on their surfaces has yielded specific homing peptides for a large number of normal tissues. The tissue-specific endothelial molecules to which the phage peptides home may serve as receptors for metastasizing malignant cells. Probing of tumor vasculature has yielded peptides that home to endothelial receptors expressed selectively in angiogenic neovasculature. These receptors, and those specific for the vasculature of individual normal tissues, are likely to be useful in targeting therapies to specific sites.

Notes: Abstract The tripartite subdivision of lymphocytes into B cells, alphabeta T cells, and gammadelta cells has been conserved seemingly since the emergence of jawed vertebrates, more than 450 million years ago. Yet, while we understand much about B cells and alphabeta T cells, we lack a compelling explanation for the evolutionary conservation of gammadelta cells. Such an explanation may soon be forthcoming as advances in unraveling the biochemistry of gammadelta cell interactions are reconciled with the abnormal phenotypes of gammadelta-deficient mice and with the striking differences in gammadelta cell activities in different strains and species. In this review, the properties of gammadelta cells form a basis for understanding gammadelta cell interactions with antigens and other cells that in turn form a basis for understanding immunoprotective and regulatory functions of gammadelta cells in vivo. We conclude by considering which gammadelta cell functions may be most critical.

Notes: Abstract This review describes the contribution of noncytolytic mechanisms to the control of viral infections with a particular emphasis on the role of cytokines in these processes. It has long been known that most cell types in the body respond to an incoming viral infection by rapidly secreting antiviral cytokines such as interferon alpha/beta (IFN-alpha/beta). After binding to specific receptors on the surface of infected cells, IFN-alpha/beta has the potential to trigger the activation of multiple noncytolytic intracellular antiviral pathways that can target many steps in the viral life cycle, thereby limiting the amplification and spread of the virus and attenuating the infection. Clearance of established viral infections, however, requires additional functions of the immune response. The accepted dogma is that complete clearance of intracellular viruses by the immune response depends on the destruction of infected cells by the effector cells of the innate and adaptive immune system [natural killer (NK) cells and cytotoxic T cells (CTLs)]. This notion, however, has been recently challenged by experimental evidence showing that much of the antiviral potential of these cells reflects their ability to produce antiviral cytokines such as IFN-gamma and tumor necrosis factor (TNF)-alpha at the site of the infection. Indeed, these cytokines can purge viruses from infected cells noncytopathically as long as the cell is able to activate antiviral mechanisms and the virus is sensitive to them. Importantly, the same cytokines also control viral infections indirectly, by modulating the induction, amplification, recruitment, and effector functions of the immune response and by upregulating antigen processing and display of viral epitopes at the surface of infected cells. In keeping with these concepts, it is not surprising that a number of viruses encode proteins that have the potential to inhibit the antiviral activity of cytokines.

Notes: Abstract Recent advances in the understanding of T cell activation have led to new therapeutic approaches in the treatment of immunological disorders. One attractive target of intervention has been the blockade of T cell costimulatory pathways, which result in more selective effects on only those T cells that have encountered specific antigen. In fact, in some instances, costimulatory pathway antagonists can induce antigen-specific tolerance that prevents the progression of autoimmune diseases and organ graft rejection. In this review, we summarize the current understanding of these complex costimulatory pathways including the individual roles of the CD28, CTLA-4, B7-1 (CD80), and B7-2 (CD86) molecules. We present evidence that suggests that multiple mechanisms contribute to CD28/B7-mediated T cell costimulation in disease settings that include expansion of activated pathogenic T cells, differentiation of Th1/Th2 cells, and the migration of T cells into target tissues. Additionally, the negative regulatory role of CTLA-4 in autoimmune diseases and graft rejection supports a dynamic but complex process of immune regulation that is prominent in the control of self-reactivity. This is most apparent in regulation of the CD4+CD25+CTLA-4+ immunoregulatory T cells that control multiple autoimmune diseases. The implications of these complexities and the potential for use of these therapies in clinical immune intervention are discussed.

Notes: Abstract The bare lymphocyte syndrome (BLS) is a hereditary immunodeficiency resulting from the absence of major istocompatibility complex class II (MHCII) expression. Considering the central role of MHCII molecules in the development and activation of CD4+ T cells, it is not surprising that the immune system of the patients is severely impaired. BLS is the prototype of a "disease of gene regulation." The affected genes encode RFXANK, RFX5, RFXAP, and CIITA, four regulatory factors that are highly specific and essential for MHCII genes. The first three are subunits of RFX, a trimeric complex that binds to all MHCII promoters. CIITA is a non-DNA-binding coactivator that functions as the master control factor for MHCII expression. The study of RFX and CIITA has made major contributions to our comprehension of the molecular mechanisms controlling MHCII genes and has made this system into a textbook model for the regulation of gene expression.

Notes: Abstract The human T cell leukemia virus-1 (HTLV-1) is a retrovirus that causes adult T cell leukemia (ATL) and neurological disorder, the tropical spastic paraparesis (HAM/TSP). The pathogenesis apparently results from the pleiotropic function of Tax protein, which is a key regulator of viral replication. Tax exerts (a) trans-activation and -repression of transcription of different sets of cellular genes through binding to groups of transcription factors and coactivators, (b) dysregulation of cell cycle through binding to inhibitors of CDK4/6, and (c) inhibition of some tumor suppressor proteins. These effects on a wide variety of cellular targets seem to cooperate in promoting cell proliferation. This is an effective viral strategy to amplify its proviral genome through replication of infected cells; ultimately it results in cell transformation and leukemogenesis.

Notes: Abstract Helicobacter pylori is a gram negative, spiral, microaerophylic bacterium that infects the stomach of more than 50% of the human population worldwide. It is mostly acquired during childhood and, if not treated, persists chronically, causing chronic gastritis, peptic ulcer disease, and in some individuals, gastric adenocarcinoma and gastric B cell lymphoma. The current therapy, based on the use of a proton-pump inhibitor and antibiotics, is efficacious but faces problems such as patient compliance, antibiotic resistance, and possible recurrence of infection. The development of an efficacious vaccine against H. pylori would thus offer several advantages. Various approaches have been followed in the development of vaccines against H. pylori, most of which have been based on the use of selected antigens known to be involved in the pathogenesis of the infection, such as urease, the vacuolating cytotoxin (VacA), the cytotoxin-associated antigen (CagA), the neutrophil-activating protein (NAP), and others, and intended to confer protection prophylactically and/or therapeutically in animal models of infection. However, very little is known of the natural history of H. pylori infection and of the kinetics of the induced immune responses. Several lines of evidence suggest that H. pylori infection is accompanied by a pronounced Th1-type CD4+ T cell response. It appears, however, that after immunization, the antigen-specific response is predominantly polarized toward a Th2-type response, with production of cytokines that can inhibit the activation of Th1 cells and of macrophages, and the production of proinflammatory cytokines. The exact effector mechanisms of protection induced after immunization are still poorly understood. The next couple of years will be crucial for the development of vaccines against H. pylori. Several trials are foreseen in humans, and expectations are that most of the questions being asked now on the host-microbe interactions will be answered.

Notes: Abstract The rapid and devastating spread of the AIDS epidemic in the developing world as well as the difficulties associated with delivering antiretroviral drugs in affected countries underscore the urgent need for the development of a safe and effective AIDS vaccine. In this review, we discuss recent advances in our understanding of the cellular and humoral immune responses to human immunodeficiency virus type 1 (HIV-1) infection. We then describe vaccine strategies that have been explored and discuss the evidence suggesting that cellular immune responses elicited by novel vaccine modalities may attenuate clinical disease caused by HIV-1.

Notes: Abstract T cells that can respond to self-antigens are present in the peripheral immune repertoire of all healthy individuals. Recently we have found that unmanipulated SJL mice that are highly susceptible to EAE also maintain a very high frequency of T cells responding to an encephalitogenic epitope of a myelin antigen proteolipid protein (PLP) 139-151 in the peripheral repertoire. This is not due to lack of expression of myelin antigens in the thymus resulting in escape of PLP 139-151 reactive cells from central tolerance, but is due to expression of a splice variant of PLP named DM20, which lacks the residues 116-150. In spite of this high frequency, the PLP 139-151 reactive cells remain undifferentiated in the periphery and do not induce spontaneous EAE. In contrast, SJL TCR transgenic mice expressing a receptor derived from a pathogenic T cell clone do develop spontaneous disease. This may be because in normal mice, autoreactive cells are kept in check by an alternate PLP 139-151 reactive nonpathogenic repertoire, which maintains a balance that keeps them healthy. If this is the case, selective activation of one repertoire or the other may alter susceptibility to autoimmune disease. Since T cells are generally cross-reactive, besides responding to nonself-antigens, they also maintain significant responses to self-antigens. Based on the PLP 139-151 system, we propose a model in which activation with foreign antigens can result in the generation of pathogenic memory T cells that mediate autoimmunity. We also outline circumstances under which activation of self-reactive T cells with foreign antigens can generate selective tolerance and thus generate protective/regulatory memory against self while still maintaining significant responses against foreign antigens. This provides a mechanism by which the fidelity and specificity of the immune system against foreign antigens is improved without increasing the potential for developing an autoimmune disease.

Notes: Abstract Whether B-1a (CD5+) cells are a distinct lineage derived from committed fetal/neonatal precursors or arise from follicular B-2 cells in response to BCR ligation and other, unknown signals remains controversial. Recent evidence indicates that B-1a cells can derive from adult precursors expressing an appropriate specificity when the (self-) antigen is present. Antibody specificity determines whether a B cell expressing immunoglobulin transgenes has a B-2, B-1a or marginal zone (MZ) phenotype. MZ cells share many phenotypic characteristics of B-1 cells and, like them, appear to develop in response to T independent type 2 antigens. Because fetal-derived B cell progenitors fail to express terminal deoxynucleotidyl transferase (TdT) and for other reasons, they are likely to express a repertoire that allows selection into the B-1a population. As it is selected by self-antigen, the B-1 repertoire tends to be autoreactive. This potentially dangerous repertoire is also useful, as B-1 cells are essential for resistance to several pathogens and they play an important role in mucosal immunity. The CD5 molecule can function as a negative regulator of BCR signaling that may help prevent inappropriate activation of autoreactive B-1a cells.

Notes: Abstract The development of the immune system and the host response to microbial infection rely on the activation and silencing of numerous, differentially expressed genes. Since the mid-1980s, a primary goal has been to identify transcription factors that regulate specific genes and specific immunological processes. More recently, there has been a growing appreciation of the role of chromatin structure in gene regulation. Before most activators of a gene access their binding sites, a transition from a condensed to a decondensed chromatin structure appears to take place. The activation of transcription is then accompanied by the remodeling of specific nucleosomes. Conversely, the acquisition of a more condensed chromatin structure is often associated with gene silencing. Chromatin structure is a particularly significant contributor to gene regulation because it is likely to be a major determinant of cell identity and cell memory. That is, the propagation of decondensed chromatin at specific loci through DNA replication and cell division helps a cell remember which genes are expressed constitutively in that cell type or are poised for expression upon exposure to a stimulus. Here we review recent progress toward understanding the role of chromatin in the immune system. The interleukin-4 gene serves as a primary model for exploring the events involved in the acquisition and heritable maintenance of a decondensed chromatin structure. Studies of the interleukin-12 p40 and interferon-beta genes are then reviewed for insight into the mechanisms by which the remodeling of specific nucleosomes in the vicinity of a promoter can contribute to rapid activation following cell stimulation. Finally, basic principles of gene silencing are discussed.

Notes: Abstract Immune cells are activated as a result of productive interactions between ligands and various receptors known as immunoreceptors. These receptors function by recruiting cytoplasmic protein tyrosine kinases, which trigger a unique phosphorylation signal leading to cell activation. In the recent past, there has been increasing interest in elucidating the processes involved in the negative regulation of immunoreceptor-mediated signal transduction. Evidence is accumulating that immunoreceptor signaling is inhibited by complex and highly regulated mechanisms that involve receptors, protein tyrosine kinases, protein tyrosine phosphatases, lipid phosphatases, ubiquitin ligases, and inhibitory adaptor molecules. Genetic evidence indicates that this inhibitory machinery is crucial for normal immune cell homeostasis.

Notes: Abstract The phagocytic response of innate immune cells such as macrophages is defined by the activation of complex signaling networks that are stimulated by microbial contact. Many individual proteins have been demonstrated to participate in phagocytosis, and the application of high-throughput tools has indicated that many more remain to be described. In this review, we examine this complexity and describe how during recognition, multiple receptors are simultaneously engaged to mediate internalization, activate microbial killing, and induce the production of inflammatory cytokines and chemokines. Many signaling molecules perform multiple functions during phagocytosis, and these molecules are likely to be key regulators of the process. Indeed, pathogenic microorganisms target many of these molecules in their attempts to evade destruction.

Notes: Abstract My work on basic and clinical immunology has focused on the regulation of the human immune response and how its dysregulation can lead to immunodeficiency, autoimmune, and malignant disorders. The early focus in our laboratory was on pathogenic mechanisms underlying hypogammaglobulinemia. Our demonstration of active suppression by human suppressor T cells changed thinking about the pathogenesis of certain immunodeficiency disorders. Recently we have focused on the cytokines interleukin-2 (IL-2) and IL-15, which have competitive functions in adaptive immune responses. IL-2 is necessary to destroy self-reactive lymphocytes and thus favors peripheral tolerance to self-antigens, whereas IL-15 favors the persistence of lymphocytes involved in the memory and effector responses to invading pathogens but risks the development of inflammatory autoimmune diseases. Our murine anti-Tac monoclonal antibody exploits these differences, as does a humanized form (daclizumab) now approved for the prevention of renal allograft rejection. New forms of therapy directed at IL-2 and IL-15 receptors may be effective against certain neoplastic diseases and autoimmune disorders and in the prevention of allograft rejection.

Notes: Abstract BAFF, a member of the TNF family, is a fundamental survival factor for transitional and mature B cells. BAFF overexpression leads to an expanded B cell compartment and autoimmunity in mice, and elevated amounts of BAFF can be found in the serum of autoimmune patients. APRIL is a related factor that shares receptors with BAFF yet appears to play a different biological role. The BAFF system provides not only potential insight into the development of autoreactive B cells but a relatively simple paradigm to begin considering the balancing act between survival, growth, and death that affects all cells.

Notes: Abstract T cell anergy is a tolerance mechanism in which the lymphocyte is intrinsically functionally inactivated following an antigen encounter, but remains alive for an extended period of time in a hyporesponsive state. Models of T cell anergy affecting both CD4+ and CD8+ cells fall into two broad categories. One, clonal anergy, is principally a growth arrest state, whereas the other, adaptive tolerance or in vivo anergy, represents a more generalized inhibition of proliferation and effector functions. The former arises from incomplete T cell activation, is mostly observed in previously activated T cells, is maintained by a block in the Ras/MAP kinase pathway, can be reversed by IL-2 or anti-OX40 signaling, and usually does not result in the inhibition of effector functions. The latter is most often initiated in naive T cells in vivo by stimulation in an environment deficient in costimulation or high in coinhibition. Adaptive tolerance can be induced in the thymus or in the periphery. The cells proliferate and differentiate to varying degrees and then downregulate both functions in the face of persistent antigen. The state involves an early block in tyrosine kinase activation, which predominantly inhibits calcium mobilization, and an independent mechanism that blocks signaling through the IL-2 receptor. Adaptive tolerance reverses in the absence of antigen. Aspects of both of the anergic states are found in regulatory T cells, possibly preventing them from dominating initial immune responses to foreign antigens and shutting down such responses prematurely.

Notes: Abstract The cells of both the adaptive and innate immune systems express a dizzying array of receptors that transduce and integrate an enormous amount of information about the environment that allows the cells to mount effective immune responses. Over the past several years, significant advances have been made in elucidating the molecular details of signal cascades initiated by the engagement of immune cell receptors by their ligands. Recent evidence indicates that immune receptors and components of their signaling cascades are spatially organized and that this spatial organization plays a central role in the initiation and regulation of signaling. A key organizing element for signaling receptors appears to be cholesterol- and sphingolipid-rich plasma membrane microdomains termed lipid rafts. Research into the molecular basis of the spatial segregation and organization of signaling receptors provided by rafts is adding fundamentally to our understanding of the initiation and prolongation of signals in the immune system.

Notes: Abstract Allergic individuals exposed to minute quantities of allergen experience an immediate response. Immediate hypersensitivity reflects the permanent sensitization of mucosal mast cells by allergen-specific IgE antibodies bound to their high-affinity receptors (FcepsilonRI). A combination of factors contributes to such long-lasting sensitization of the mast cells. They include the homing of mast cells to mucosal tissues, the local synthesis of IgE, the induction of FcepsilonRI expression on mast cells by IgE, the consequent downregulation of FcgammaR (through an insufficiency of the common gamma-chains), and the exceptionally slow dissociation of IgE from FcepsilonRI. To understand the mechanism of the immediate hypersensitivity phenomenon, we need explanations of why IgE antibodies are synthesized in preference to IgG in mucosal tissues and why the IgE is so tenaciously retained on mast cell-surface receptors. There is now compelling evidence that the microenvironment of mucosal tissues of allergic disease favors class switching to IgE; and the exceptionally high affinity of IgE for FcepsilonRI can now be interpreted in terms of the recently determined crystal structures of IgE-FcepsilonRI and IgG-FcgammaR complexes. The rate of local IgE synthesis can easily compensate for the rate of the antibody dissociation from its receptors on mucosal mast cells. Effective mechanisms ensure that allergic reactions are confined to mucosal tissues, thereby minimizing the risk of systemic anaphylaxis.

Notes: Abstract Over the past decade, key protein interactions contributing to T cell antigen recognition have been characterized in molecular detail. These have included interactions involving the T cell antigen receptor (TCR) itself, its coreceptors CD4 and CD8, the accessory molecule CD2, and the costimulatory receptors CD28 and CTLA-4. A clear view is emerging of how these molecules interact with their ligands at the cell-cell interface. Structural and binding studies have confirmed that the proteins span small but comparable distances and that, overall, they interact very weakly. However, there have been important surprises as well: that TCR interactions with peptide-MHC are topologically constrained and characterized by considerable conformational flexibility at the binding interface; that coreceptors engage peptide-MHC with extraordinarily fast kinetics and at angles apparently precluding direct interactions with the TCR bound to the same peptide-MHC; that the structural mechanisms allowing recognition by costimulatory and accessory molecules to be weak and yet specific are very heterogeneous; and that because of differences in both binding affinity and stoichiometry, there is enormous variation in the stability of the various costimulatory receptor/ligand complexes. These studies provide the necessary framework for exploring how these molecular interactions initiate T cell activation.

Notes: Abstract Stem cell biology is scientifically, clinically, and politically a current topic. The hematopoietic stem cell, the common ancestor of all types of blood cells, is one of the best-characterized stem cells in the body and the only stem cell that is clinically applied in the treatment of diseases such as breast cancer, leukemias, and congenital immunodeficiencies. Multicolor cell sorting enables the purification not only of hematopoietic stem cells, but also of their downstream progenitors such as common lymphoid progenitors and common myeloid progenitors. Recent genetic approaches including gene chip technology have been used to elucidate the gene expression profile of hematopoietic stem cells and other progenitors. Although the mechanisms that control self-renewal and lineage commitment of hematopoietic stem cells are still ambiguous, recent rapid advances in understanding the biological nature of hematopoietic stem and progenitor cells have broadened the potential application of these cells in the treatment of diseases.

Notes: Complement has both beneficial and deleterious roles in the pathogenesis of systemic lupus erythematosus (SLE). On the one hand, patients with SLE present with decreased complement levels and with complement deposition in inflammed tissues, suggestive of a harmful role of complement in the effector phase of disease. On the other hand, homozygous deficiency of any of the classical pathway proteins is strongly associated with the development of SLE. There are two main hypotheses to explain these observations. The first invokes an important role for complement in the physiological waste-disposal mechanisms of dying cells and immune complexes. The second hypothesis is based around the role of complement in determining the activation thresholds of B and T lymphocytes, with the proposal that complement deficiency causes incomplete maintenance of peripheral tolerance. These two hypotheses are not mutually exclusive. In addition, there is evidence for a contribution from other genetic factors in determining the phenotype of disease in the absence of complement.

Notes: Cytokines are an integral component of the adaptive and innate immune responses. The signaling pathways triggered by the engagement of cytokines with their specific cell surface receptors have been extensively studied and have provided a profound understanding of the intracellular machinery that translates exposure of cells to cytokine to a coordinated biological response. It has also become clear that cells have evolved sophisticated mechanisms to prevent excessive responses to cytokines. In this review we focus on the suppressors of cytokine signaling (SOCS) family of cytoplasmic proteins that completes a negative feedback loop to attenuate signal transduction from cytokines that act through the janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. SOCS proteins inhibit components of the cytokine signaling cascade via direct binding or by preventing access to the signaling complex. The SOCS proteins also appear to target signal transducers for proteasomal destruction. Analyses of genetically modified mice in which SOCS proteins are overexpressed or deleted have established that this family of negative regulators has indispensable roles in regulating cytokine responses in cells of the immune system as well as other tissues. Emerging evidence also suggests that disruption of SOCS expression or activity is associated with several immune and inflammatory diseases, raising the prospect that manipulation of SOCS activity may provide a novel future therapeutic strategy in the management of immunological disorders.

Notes: The factors affecting T cell viability vary depending on the type and status of the T cell involved. Naive T cells die via a Bcl-2/Bim dependent route. Their deaths are prevented in animals by IL-7 and contact with MHC. Activated T cells die in many different ways. Among these is a pathway involving signals that come from outside the T cell and affect it via surface receptors such as Fas. Activated T cells also die through a pathway driven by signals generated within the T cell itself, a cell autonomous route. This pathway involves members of the Bcl-2 family, in particular Bcl-2, Bcl-xl, Bim, and probably Bak. The viability of CD8+ and CD4+ memory T cells is controlled in different ways. CD8+ memory T cells are maintained by IL-15 and IL-7. The control of CD4+ memory T cells is more mysterious, with roles reported for IL-7 and/or contact via the TCR.

Notes: The present review focuses on the concept that cellular and humoral immunity to the phylogenetically highly conserved antigen heat shock protein 60 (HSP60) is the initiating mechanism in the earliest stages of atherosclerosis. Subjecting arterial endothelial cells to classical atherosclerosis risk factors leads to the expression of HSP60 that then may serve as a target for pre-existent cross-reactive antimicrobial HSP60 immunity or bona fide autoimmune reactions induced by biochemically altered autologous HSP60. Endothelial cells can also bind microbial or autologous HSP60 via Toll-like receptors, providing another possibility for targetting adaptive or innate immunological effector mechanisms.

Notes: Integrin receptors mediate adhesive events that are critical for a specific and effective immune response to foreign pathogens. Integrin-dependent interactions of lymphocytes and antigen-presenting cells (APCs) to endothelium regulate the efficiency and specificity of trafficking into secondary lymphoid organs and peripheral tissue. Within these sites, integrins facilitate cell movement via interactions with the extracellular matrix, and promote and stabilize antigen-specific interactions between T lymphocytes and APCs that are critical for initiating T cell-activation events. In this review, we discuss the role of integrins in T cell-mediated immunity, with a focus on how these receptors participate in lymphocyte recirculation and T cell activation, how antigen stimulation regulates integrin activity, and how integrins define functionally unique subsets of T cells and APCs.

Notes: Naturally occurring CD4+ regulatory T cells, the majority of which express CD25, are engaged in dominant control of self-reactive T cells, contributing to the maintenance of immunologic self-tolerance. Their depletion or functional alteration leads to the development of autoimmune disease in otherwise normal animals. The majority, if not all, of such CD25+CD4+ regulatory T cells are produced by the normal thymus as a functionally distinct and mature subpopulation of T cells. Their repertoire of antigen specificities is as broad as that of naive T cells, and they are capable of recognizing both self and nonself antigens, thus enabling them to control various immune responses. In addition to antigen recognition, signals through various accessory molecules and via cytokines control their activation, expansion, and survival, and tune their suppressive activity. Furthermore, the generation of CD25+CD4+ regulatory T cells in the immune system is at least in part developmentally and genetically controlled. Genetic defects that primarily affect their development or function can indeed be a primary cause of autoimmune and other inflammatory disorders in humans. Based on recent advances in our understanding of the cellular and molecular basis of this T cell-mediated immune regulation, this review discusses how naturally arising CD25+CD4+ regulatory T cells contribute to the maintenance of immunologic self-tolerance and negative control of various immune responses, and how they can be exploited to prevent and treat autoimmune disease, allergy, cancer, and chronic infection, or establish donor-specific transplantation tolerance.

Notes: Abstract Our understanding of the X-linked lymphoproliferative syndrome (XLP) has advanced significantly in the last two years. The gene that is altered in the condition (SAP/SH2D1A) has been cloned and its protein crystal structure solved. At least two sets of target molecules for this small SH2 domain-containing protein have been identified: A family of hematopoietic cell surface receptors, i.e. the SLAM family, and a second molecule, which is a phosphorylated adapter. A SAP-like protein, EAT-2, has also been found to interact with this family of surface receptors. Several lines of evidence, including structural studies and analyses of missense mutations in XLP patients, support the notion that SAP/SH2D1A is a natural inhibitor of SH2-domain-dependent interactions with members of the SLAM family. However, details of its role in signaling mechanisms are yet to be unravelled. Further analyses of the SAP/SH2D1A gene in XLP patients have made it clear that the development of dys-gammaglobulinemia and B cell lymphoma can occur without evidence of prior EBV infection. Moreover, preliminary results of virus infections of a mouse in which the SAP/SH2D1A gene has been disrupted suggest that EBV infection is not per se critical for the development of XLP phenotypes. It appears therefore that the SAP/SH2D1A gene controls signaling via the SLAM family of surface receptors and thus may play a fundamental role in T cell and APC interactions during viral infections.

Notes: Abstract T cell activation is dependent upon signals delivered through the antigen-specific T cell receptor and accessory receptors on the T cell. A primary costimulatory signal is delivered through the CD28 receptor after engagement of its ligands, B7-1 (CD80) or B7-2 (CD86). Engagement of CTLA-4 (CD152) by the same B7-1 or B7-2 ligands results in attenuation of T cells responses. Recently, molecular homologs of CD28 and CTLA-4 receptors and their B7-like ligands have been identified. ICOS is a CD28-like costimulatory receptor with a unique B7-like ligand. PD-1 is an inhibitory receptor, with two B7-like ligands. Additional members of B7 and CD28 gene families have been proposed. Integration of signals through this family of costimulatory and inhibitory receptors and their ligands is critical for activation of immune responses and tolerance. Understanding these pathways will allow development of new strategies for therapeutic intervention in immune-mediated diseases.

Notes: Abstract The innate immune system is a universal and ancient form of host defense against infection. Innate immune recognition relies on a limited number of germline-encoded receptors. These receptors evolved to recognize conserved products of microbial metabolism produced by microbial pathogens, but not by the host. Recognition of these molecular structures allows the immune system to distinguish infectious nonself from noninfectious self. Toll-like receptors play a major role in pathogen recognition and initiation of inflammatory and immune responses. Stimulation of Toll-like receptors by microbial products leads to the activation of signaling pathways that result in the induction of antimicrobial genes and inflammatory cytokines. In addition, stimulation of Toll-like receptors triggers dendritic cell maturation and results in the induction of costimulatory molecules and increased antigen-presenting capacity. Thus, microbial recognition by Toll-like receptors helps to direct adaptive immune responses to antigens derived from microbial pathogens.

Notes: Abstract Lymphocytes arise from hematopoietic stem cells through the coordinated action of transcription factors. The E proteins (E12, E47, HEB and E2-2) have emerged as key regulators of both B and T lymphocyte differentiation. This review summarizes the current data and examines the various functions of E proteins and their antagonists, Id2 and Id3, throughout lymphoid maturation. Beyond an established role in B and T lineage commitment, E proteins continue to be essential at subsequent stages of development. E protein activity regulates the expression of surrogate and antigen receptor genes, promotes Ig and TCR rearrangements, and coordinates cell survival and proliferation with developmental progression in response to TCR signaling. Finally, this review also discusses the role of E47 as a tumor suppressor.

Notes: Abstract Heat shock proteins are abundant soluble intracellular proteins, present in all cells. Members of the heat shock protein family bind peptides including antigenic peptides generated within cells. Heat shock proteins also interact with antigen presenting cells through CD91 and other receptors, eliciting a cascade of events including re-presentation of heat shock protein-chaperoned peptides by MHC, translocation of NFkappaB into the nuclei and maturation of dendritic cells. These consequences point to a key role of heat shock proteins in fundamental immunological phenomena such as activation of antigen presenting cells, indirect presentation (or cross-priming), and chaperoning of peptides during antigen presentation. Heat shock proteins appear to have been involved in innate immune responses since the emergence of phagocytes in early multicellular organisms and to have been commandeered for adaptive immune responses with the advent of specificity. These properties of heat shock proteins also allow them to be used for immunotherapy of cancers and infections in novel ways.

Notes: Abstract In recent years the status of the inflammatory bowel diseases (IBDs) as canonical autoimmune diseases has risen steadily with the recognition that these diseases are, at their crux, abnormalities in mucosal responses to normally harmless antigens in the mucosal microflora and therefore responses to antigens that by their proximity and persistence are equivalent to self-antigens. This new paradigm is in no small measure traceable to the advent of multiple models of mucosal inflammation whose very existence is indicative of the fact that many types of immune imbalance can lead to loss of tolerance for mucosal antigens and thus inflammation centered in the gastrointestinal tract. We analyze the immunology of the IBDs through the lens of the murine models, first by drawing attention to their common features and then by considering individual models at a level of detail necessary to reveal their individual capacities to provide insight into IBD pathogenesis. What emerges is that murine models of mucosal inflammation have given us a road map that allows us to begin to define the immunology of the IBDs in all its complexity and to find unexpected ways to treat these diseases.

Notes: Abstract Humans are exposed to a variety of environmental mycobacteria (EM), and most children are inoculated with live Bacille Calmette-Guerin (BCG) vaccine. In addition, most of the world's population is occasionally exposed to human-borne mycobacterial species, which are less abundant but more virulent. Although rarely pathogenic, mildly virulent mycobacteria, including BCG and most EM, may cause a variety of clinical diseases. Mycobacterium tuberculosis, M. leprae, and EM M. ulcerans are more virulent, causing tuberculosis, leprosy, and Buruli ulcer, respectively. Remarkably, only a minority of individuals develop clinical disease, even if infected with virulent mycobacteria. The interindividual variability of clinical outcome is thought to result in part from variability in the human genes that control host defense. In this well-defined microbiological and clinical context, the principles of mouse immunology and the methods of human genetics can be combined to facilitate the genetic dissection of immunity to mycobacteria. The natural infections are unique to the human model, not being found in any of the animal models of experimental infection. We review current genetic knowledge concerning the simple and complex inheritance of predisposition to mycobacterial diseases in humans. Rare patients with Mendelian disorders have been found to be vulnerable to BCG, a few EM, and M. tuberculosis. Most cases of presumed Mendelian susceptibility to these and other mycobacterial species remain unexplained. In the general population leprosy and tuberculosis have been shown to be associated with certain human genetic polymorphisms and linked to certain chromosomal regions. The causal vulnerability genes themselves have yet to be identified and their pathogenic alleles immunologically validated. The studies carried out to date have been fruitful, initiating the genetic dissection of protective immunity against a variety of mycobacterial species in natural conditions of infection. The human model has potential uses beyond the study of mycobacterial infections and may well become a model of choice for the investigation of immunity to infectious agents.

Notes: Abstract In contrast to T cell receptors, signal transducing cell surface membrane molecules involved in the regulation of responses by cells of the innate immune system employ structures that are encoded in the genome rather than generated by somatic recombination and that recognize either classical MHC-I molecules or their structural relatives (such as MICA, RAE-1, or H-60). Considerable progress has recently been made in our understanding of molecular recognition by such molecules based on the determination of their three-dimensional structure, either in isolation or in complex with their MHC-I ligands. Those best studied are the receptors that are expressed on natural killer (NK) cells, but others are found on populations of T cells and other hematopoietic cells. These molecules fall into two major structural classes, those of the immunoglobulin superfamily (KIRs and LIRs) and of the C-type lectin-like family (Ly49, NKG2D, and CD94/NKG2). Here we summarize, in a functional context, the structures of the murine and human molecules that have recently been determined, with emphasis on how they bind different regions of their MHC-I ligands, and how this allows the discrimination of tumor or virus-infected cells from normal cells of the host.

Notes: Abstract Computer simulation of clinical trials has evolved over the past two decades from a simple instructive game to "full" simulation models yielding pharmacologically sound, realistic trial outcomes. The need to make drug development more efficient and informative and the awareness that many industries make extensive use of simulation in product development have advanced considerably the use of simulation of clinical trials in pharmaceutical product development over the past decade. The structural and stochastic components of trial simulation models are explained as a prelude to a listing of representative simulation projects, reflecting investigative applications of statistical methods, trial design comparisons, and full simulation of new drugs being developed. Lessons learned from these projects are reviewed in the context of their current impact and potential for influencing the future of drug development.

Notes: Abstract Technological advances continue to be a central driving force in the acceleration of the drug discovery process. Combinatorial chemistry methods, developed over the past 15 years, represent a paradigm shift in drug discovery. Initially viewed as a curiosity by the pharmaceutical industry, combinatorial chemistry is now recognized as an essential tool that decreases the time of discovery and increases the throughput of chemical screening by as much as 1000-fold. The use of parallel array synthesis approaches and mixture-based combinatorial libraries for drug discovery is reviewed.