ALBERT

Description: The precise role of intravascular tissue factor (TF) remains poorly defined, due to the limited availability of assays capable of measuring circulating TF procoagulant activity (PCA). As a model of inflammation-associated intravascular thrombin generation, we studied 18 volunteers receiving an infusion of endotoxin. A novel assay that measures microparticle (MP)-associated TF PCA from a number of cellular sources (but not platelets) demonstrated an 8-fold increase in activity at 3 to 4 hours after endotoxin administration (P 〈 .001), with a return to baseline by 8 hours. TF antigen-positive MPs isolated from plasma were visualized by electron microscopy. Interindividual MP-associated TF response to lipopolysaccharide (LPS) was highly variable. In contrast, a previously described assay that measurestotal (cell and MP-borne) whole-blood TF PCA demonstrated a more modest increase, with a peak in activity (1.3-fold over baseline; P 〈 .000 01) at 3 to 4 hours, and persistence for more than 24 hours. This surprisingly modest increase in whole-blood TF activity is likely explained by a profound although transient LPS-induced monocytopenia. MP-associated TF PCA was highly correlated with whole-blood TF PCA and total number of circulating MPs, and whole-blood TF PCA was highly correlated with TF mRNA levels. (Blood. 2004;103:4545-4553)

Description: Chemokines acting through G-protein coupled receptors play an essential role in both the immune and inflammatory responses. Phosphatidylinositol 3-kinase (PI3K) and phospholipase C (PLC) are two distinct signaling molecules that have been proposed as potential candidates in the regulation of this process. Studies with knockout mice have demonstrated a critical role for PI3Kγ, but not PLCβ, in Gαi-coupled receptor-mediated neutrophil chemotaxis. We compared the chemotactic response of peripheral T-cells derived from wild type mice with mice containing loss-of-function mutations of either PI3Kγ, or both of the two predominant lymphocyte PLCβ isoforms (PLCβ2 and PLCβ3). In contrast to neutrophils, loss of PI3Kγ did not significantly impair T-cell migration in vitro, although PI3K pharmacologic inhibitor experiments suggest that another isoform of this enzyme might contribute to T-cell migration. However, loss of PLCβ2β3 decreased chemokine-stimulated T-cell migration in vitro. Chelation of intracellular calcium by BAPTA-AM and Quin-2 AM decreased the chemotactic response of wild type lymphocytes, but pharmacologic inhibition of PKC isoforms by GF109203x did not impair T-cell migration. This suggests that the T-cell migration defect seen in the PLCβ2β3-null T-cells may be due to an impaired ability to increase the cytoplasmic calcium concentration, while there appears to be little requirement for PKC activity. Indeed, SDF-1α-induced calcium efflux was not detected in the PLCβ2β3-null lymphocytes. Compared to fluorescently labeled wild type T-cells, labeled PLCβ2β3 knockout T-cells migrated less efficiently into secondary lymphoid organs of recipient mice. This demonstrates that PLCβ is also required for migration in vivo. PLCβ2β3-null mice develop spontaneous skin ulcers starting around 3 months of age. Histological examination of the lesions revealed a dense inflammatory infiltrate composed of neutrophils, macrophages, and plasma cells, consistent with acute and chronic inflammation. Remarkably, lymphocytes, typical of chronic inflammation, were rare to absent by histology and by paraffin immunohistochemistry for CD3, also consistent with an in vivo migratory defect of T-cells. These results show that phospholipid second messengers generated by PLCβ and isoforms of PI3K, other than PI3Kγ, play a critical role in lymphocyte chemotaxis. Collectively, our data demonstrate that although PLCβ-mediated signaling plays no role in neutrophil chemotaxis, it makes a substantial contribution to this process within T-lymphocytes.

Description: Human γδ T lymphocytes respond to viral, bacterial, protozoal, and tumoral antigens, but their precise function remains unknown. In adults the major circulating γδ T-cell subset expresses the Vγ9Vδ2 T-cell receptor and responds to protease-resistant phosphorylated derivatives found in many pathogens. In this study we show that activation of Vδ2+ cells with the nonpeptidic antigen isopentenyl pyrophosphate (IPP) rapidly induces (within 4-12 hours) the C-C chemokines MIP-1, MIP-1β, and lymphotactin but not MCP-1. The most robust response was obtained for MIP-1β. IPP induction of MIP-1 and MIP-1β was not affected by costimulation with interleukin-4 (IL-4), IL-10, TGF-β, or interferon-γ (INF-γ). However, IL-12 significantly enhanced IPP-induced expression and release of MIP-1 that was down-regulated by TGF-β whereas the induction of MIP-1β by IPP+IL-12 was refractory to cotreatment with TGFβ indicating that these chemokines are differentially regulated by these cytokines. Vδ2+ T cells also expressed a wide range of C-C chemokine receptors including CCR1, CCR5, and CCR8, all of which were down-regulated following activation. We conclude that Vδ2+ cells can be rapidly induced by components of bacterial cell walls to express high levels of proinflammatory chemokines, supporting an important role for these cells in the early stages of the inflammatory responses to many common pathogens. (Blood. 2000, 95:39-47)

Description: Patients who develop respiratory failure requiring mechanical ventilation after hematopoietic stem cell transplantation (HSCT) have very high mortality. Several investigators have identified prognostic features that can be used to identify a subset of these patients who are virtually certain to die, yet these have never been prospectively assessed. The objectives of this study were to determine the accuracy of published prognostic features for mortality and to determine the survival of patients who recover from respiratory failure. A systematic review of the literature was undertaken to identify reported poor prognostic features and survival rates. The study validated the reported poor prognostic features on a prospective, multicenter inception cohort of 226 patients with respiratory failure requiring mechanical ventilation after HSCT. The main outcome measures were determination of a baseline probability of death, drawn from literature review; likelihood ratio of mortality for each prognostic feature determined from the validation cohort; conditional probability of death in the presence of each feature; and 6-month survival of those who recover. Patients requiring mechanical ventilation after HSCT have a baseline probability of death of 82% to 96%. In the setting of combined hepatic and renal dysfunction, the probability of death rises to 98% to 100%. Other previously reported prognostic features are less strongly associated with mortality. For patients who recover from respiratory failure, the proportion surviving 6 months or longer ranges from 27% to 88%. It was concluded that in patients requiring mechanical ventilation after HSCT, the presence of combined hepatic and renal dysfunction is highly predictive of death. The presence of this feature may justify the recommendation to withdraw life-sustaining measures.

Description: TF is a 47 kDa cell-bound glycoprotein that initiates coagulation upon contact with factor VII(a). Both monocytes and cells derived from the vessel wall (such as endothelial cells) are capable of TF synthesis, and both intact cells and microparticles (MPs) derived from them are considered to be the principal source(s) of intravascular TF. Data from in vitro systems and animal models suggest that MP-borne TF may be transferred to activated platelets via a P-selectin dependent pathway. We previously demonstrated that during the aplastic phase of HSCT, about 55% of baseline (pre-transplant) levels of circulating whole blood TF procoagulant activity (PCA) remained detectable (Thromb & Haemost2001;85:250). This study was therefore undertaken to identify whether this residual TF activity is accounted for by intact cells or MPs, and to determine whether cells derived from the vessel wall or the hematopoietic compartment are responsible. MP-associated TF PCA was measured using a recently described MP capture assay (Blood2004;103:4545). MP-associated TF PCA declined by 89% at day 0 and by 77% at day +7 compared to baseline levels measured at day −7, with a subsequent normalization of activity paralleling engraftment. TF PCA was assayed on fractionated platelets and mononuclear cells obtained on days −7,0,7,14 and 21 from 11 patients undergoing HSCT. Mononuclear cell and platelet fractions were obtained by differential centrifugation and exposed to calcium ionophore to maximally ‘de-encrypt’ TF PCA. Following pre-incubation with FVIIa, the clotting time of added plasma was recorded, and the amount of TF calculated by reference to a standard curve generated using Innovin™. In parallel with the drop in circulating monocyte counts, a significant decline in TF PCA in both the mononuclear cell (1855±690 at day −7 vs. 74±37 pg/ml at day +7, p=0.003) and platelet (260±45 at day −7 vs. 51±16 pg/ml at day +7, p=0.05) fractions was noted. TF PCA in these fractions subsequently returned towards baseline levels with engraftment. Notably, while platelet-associated TF PCA accounted for only 12% of the total cell-associated TF PCA at baseline (day −7), it accounted for fully 59% at day 0 and 41% at day +7. This led us to postulate that transfused platelets might contribute to circulating TF during the aplastic phase. Within 1 hour of receiving leuco-depleted platelet transfusion, total cell-associated (platelet + mononuclear cell) TF PCA had increased significantly (142 ± 43 pg/ml to 317 ± 55 pg/ml, p=0.015), confirming that transfused platelets are indeed a source of TF. While this augmentation of cell-associated TF PCA was primarily seen in the platelet fraction, an increase in mononuclear cell-associated TF PCA was also noted. Conclusion: The majority of cell-associated TF PCA is associated with the mononuclear cell fraction in whole blood. However, with the onset of severe leucopenia during HSCT, the platelet pool becomes the dominant location for TF. Our data are in agreement with recent transgenic mouse model data demonstrating that the bone marrow - not the vessel wall - is the dominant source of both cell- and MP-associated intravascular TF.

Description: All eukaryotic cells contain the phospholipid phosphatidylinositol-4, 5-bisphosphate (PIP2) that serves multiple roles in signaling cascades critical for actin dynamics. Phosphatidylinositol-4-phosphate 5 kinase (PIP5K) catalyzes the synthesis of PIP2 by phosphorylating PI4P. Although the classical PIP5K isoforms (α, β, and γ) generate the same phospholipid product, the isoforms have different primary structures, are expressed at different levels in various tissues, and localize in different intracellular compartments. Therefore, it is likely that the functions of these isoforms are different as well. PIP5Kγ is unique because it associates directly with talin and consequently localizes in focal adhesion. Given the role of PIP2 in actin dynamics, we generated a murine line containing a null mutation in the PIP5Kγ gene. We found that the targeted disruption of PIP5Kγ results in early prenatal mortality that is associated with pleotropic effects involving the cardiovascular, neurologic, and hematopoietic systems. This early lethality prevented studies of hematopoietic cells derived from the bone marrow or the liver. However, we were able to analyze yolk sac progenitor cells that were treated with thrombopoietin ex vivo, differentiating them into megakaryocytes. After 5 days in culture, many of the non-adherent yolk sac progenitor cells were multinucleated, and approximately 70% expressed CD41 (αIIb), a marker of the megakaryocyte lineage. We then examined their cytoskeletal content and dynamics. Absence of PIP5Kγ had no effect on the quantity of F-actin in unstimulated or thrombin-stimulated cells that were adherent to fibrinogen or were maintained in suspension in the absence of stimulation. Next, we examined membrane dynamics during cell adhesion in real time using spinning disk video confocal microscopy. Wild type megakaryocytes actively formed and contracted lamellipodia and rapidly spread upon the fibrinogen matrix. In contrast, PIP5Kγ-null megakaryocytes continuously extended and retracted membrane blebs, rather than lamellipodia, but eventually spread as much as wild type cells. This observation is consistent with the previous suggestion that PIP2 contributes to the stable association of the membrane with the cytoskeleton. It is also noteworthy that a similar phenotype has been described in cells with defective anchoring of the membrane to the cytoskeleton because of a lack of filamin. Accordingly, our data are consistent with the hypothesis that PIP5Kγ generates compartmentalized pools of PIP2 that contribute to the association of the membrane with the cytoskeleton.

Description: Carbon monoxide (CO) at low concentrations has generated recent interest due to its ability to modulate the inflammatory response associated with chronic graft rejection, vascular injury and septic shock. Both in vivo and in vitro CO can inhibit the expression of pro-inflammatory genes such as TNFα in macrophages while simultaneously increasing the expression of the anti-inflammatory cytokine IL-10. The mechanisms by which this occurs are still unclear. To better understand the mechanisms underlying the effects of CO, we employed the Affymetrix GeneChip technology to evaluate the time-dependent expression patterns of 〉12,000 genes in macrophages stimulated with bacterial endotoxin (LPS) in the presence or absence of a low concentration of CO previously demonstrated to evoke an anti-inflammatory response. We were particularly interested whether CO would, by itself, modulate in a specific manner the expression of proteins that might explain the anti-inflammatory effects observed following subsequent administration of endotoxin. RAW 264.7 murine macrophages were grown to 75% confluency and then exposed to CO (250 ppm) for 3 hr prior to administration of LPS (10 ng/ml). At 0, 15, 30, 60, 120 and 240 min thereafter, total RNA was isolated by standard methods and the RNA was then labeled and hybridized to U74Av2 GeneChips. Of 〉12,000 genes assessed, 116 of 270 that were LPS-responsive were affected by CO treatment. CO inhibited the majority of LPS-induced pro-inflammatory cytokines and acute phase proteins including expression of early growth response-1 (Egr-1), a transcription factor that serves as a central intermediary regulating many genes. Egr-1 was nearly completely inhibited by CO as was Egr-1-dependent expression of tissue factor (TF) and PAI-1. Treatment of cells with CO alone led to a rapid early increase in PPARγ, the expression of which was essential for the anti-inflammatory effects of CO. Inhibition of PPARγ using the selective chemical inhibitor GW9662 reversed the CO inhibitory effects on LPS-induced Egr-1 and TF expression. Correlative in vivo experiments in mice showed that CO pre-treatment blocked endotoxin-induced Egr-1 expression and decreased markers of lung inflammmation the effects of which were also lost with inhibition of PPARγ. Our analyses of gene expression patterns has led to the first molecular understanding of how treatment with CO, in this case by inducing PPARγ, blocks the pro-inflammatory response. These experiments provide novel insights into the mechanisms and pathophysiology of endotoxic shock and identify cellular targets by which CO mediates these cytoprotective effects.

Description: Human γδ T lymphocytes respond to viral, bacterial, protozoal, and tumoral antigens, but their precise function remains unknown. In adults the major circulating γδ T-cell subset expresses the Vγ9Vδ2 T-cell receptor and responds to protease-resistant phosphorylated derivatives found in many pathogens. In this study we show that activation of Vδ2+ cells with the nonpeptidic antigen isopentenyl pyrophosphate (IPP) rapidly induces (within 4-12 hours) the C-C chemokines MIP-1, MIP-1β, and lymphotactin but not MCP-1. The most robust response was obtained for MIP-1β. IPP induction of MIP-1 and MIP-1β was not affected by costimulation with interleukin-4 (IL-4), IL-10, TGF-β, or interferon-γ (INF-γ). However, IL-12 significantly enhanced IPP-induced expression and release of MIP-1 that was down-regulated by TGF-β whereas the induction of MIP-1β by IPP+IL-12 was refractory to cotreatment with TGFβ indicating that these chemokines are differentially regulated by these cytokines. Vδ2+ T cells also expressed a wide range of C-C chemokine receptors including CCR1, CCR5, and CCR8, all of which were down-regulated following activation. We conclude that Vδ2+ cells can be rapidly induced by components of bacterial cell walls to express high levels of proinflammatory chemokines, supporting an important role for these cells in the early stages of the inflammatory responses to many common pathogens. (Blood. 2000, 95:39-47)