ALBERT

Description: Abstract While the scientific community has long recognized that alluvial rivers are the product of interactions between flowing water and bed material transport, it is increasingly evident that vegetation mediates these interactions and influences the stream channel characteristics. In a novel set of mobile bed laboratory experiments with variable discharge, we demonstrate that vegetation colonization affects bank erosion rates, channel shape, channel sinuosity, and bar pattern. Our analyses compared the morphological evolution of channels with initially steady bars considering the following three scenarios: (1) channel without vegetation, (2) channel with vegetation added to the floodplains, and (3) channel with vegetation added to both the floodplains and the bar surfaces that emerge at low flows. Absence of vegetation produced the widest and shallowest channel with the lowest sinuosity. Floodplain vegetation in the second scenario reduced bank erosion and resulted in a deeper and more sinuous channel with shorter bars. In the third scenario, vegetation establishment on emerging bar surfaces intensified erosion on the opposing bank, enlarging the amplitude of bends. Enhanced sedimentation on vegetated bar areas increased both bar elevation and bar length compared to the second scenario. The results show that the colonization of bar surfaces by plants creates the conditions for new floodplain and island formation, fostering channel meandering and anabranching. Finally, our experiments emphasize the role of alternating high and low flows on the morphological development of streams mediated by vegetation.

Description: Crosstalk between murine liver sinusoidal endothelial cells (LSEC) and hematopoietic stem cells during in vitro hematopoiesis. G. Luna, J. E. Cardier. Laboratorio de Patologia Celular y Molecular, Centro de Medicina Experimental, Instituto Venezolano de Investigaciones Científicas (IVIC). Apartado 21827, Caracas, Venezuela We have showed that at the liver there is a specific hematopoietic microenvironment, constituted by the liver sinusoid endothelial cells (LSEC), which are capable to support, in vitro and in vivo, not only the proliferation but also the differentiation and survival of hematopoietic stem cells (HSC). The ability of LSEC to support hematopoiesis could be related to specific hematopoietic molecules expressed by these cells. In this study, we investigate the expression of some cell adhesion molecules (VCAM-1, ICAM-1, and the integrin a4b1 ), and early acting hematopoietic cytokines (IL-6 and GM-CSF), on LSEC cocultured with HSC. The expression of VCAM-1, ICAM-1, α4β1, IL6 and GM-SCF was increased on LSEC cocultured with HSC. In contrast, a significant decrease in the expression of IL-6 and GM-CSF in the HSC derived from the same cocultures was observed. The blockade of VCAM-1 on LSEC reduced significantly the adhesion of HSC to LSEC monolayers, suggesting that this molecule is involved in the binding of HSC to LSEC microenvironments. There were not changes in the expression of the molecules evaluated when the LSEC and HSC were co-cultured in non-contact conditions, suggesting that soluble factors do not participate in regulating the expression of these molecules. Our data shows that during in vitro hematopoiesis, LSEC are activated to express molecules associated with the hematopoiesis process. LSEC activation is regulated by the contact between these cells and HSC. By expressing critical hematopoietic microenvironment molecules, LSEC may regulate the proliferation and differentiation of HSC, during liver extramedullary hematopoiesis.

Description: INTRODUCTION Besides many problematics the Covid-19 pandemic has triggered, one issue remains the care of chronically ill patients. Regarding sickle cell disease (SCD), patients often present co-morbidities that could predispose them to poor outcome if they get infected. Vaso-occlusive crisis (VOC), a characteristic manifestation of SCD, is the first cause of patients 'hospitalizations. Here, we describe how our sickle cell referral center has managed outpatient care, with the constant preoccupation of minimizing risks for our patients and avoid them unnecessary trips to heavily burdened hospital settings. DESCRIPTION OF SETTING With the outbreak of Covid-19, our primary obsession was to provide continuous care for our patients, while ensuring their safety. All appointments were canceled when possible and patients were instructed to comply with the national lock down procedures. A hotline and helpdesk were setup as the first stage of our structure. When patients described symptoms of VOC and/or light breathing difficulties, they were enlisted for daily monitoring. This stage two consisted of calling patients daily with a specific set of questions, regarding management and improvement or deterioration of their symptoms. A dedicated team of dentists, who all volunteered and received specific training, managed both stage 1 and 2, along with nurses. SCD specialists supervised these two stages for medical decisions. All symptoms were recorded and reported. If symptoms disappeared, the patient's name was discarded from the list. If there was a worsening or no improvement of the patient's condition, he was moved to stage three by the SCD expert, with the deployment of homecare service. A whole network was then setup, with the delivery of oxygen supply at the patient's house, dispatch of a medical prescription to a neighboring pharmacy and daily visits from homecare service providers. Both opioids and parenteral treatments were prescribed and monitoring was performed daily (blood pressure, temperature, respiratory rate, pain, etc...). On the first visit, a blood sample was sent to a laboratory, to allow calculation of the PRESEV score (Bartolucci et al., 2016). This score, established by team members and colleagues, assesses the risk of acute chest syndrome (ACS). Moreover, it has just been validated by a multicenter international study (PRESEV II - under writing process). In case the PRESEV score was ≤ 5, home hospitalization was pursued. In case this score was ≥11, the patient was sent to hospital for constant monitoring and full comprehensive care. For low and intermediate scores, the patient was referred to hospital for any aggravation. The helpdesk was in constant interaction with nurses and providers of homecare services and status and evolution of the patient's global condition was reported daily for medical decisions. In addition, patients with home hospitalization care were called daily by the helpdesk, to ensure proper care and satisfaction. When home hospitalization was over, the patient automatically came back to stage two for a daily follow-up until full recovery. Early discharged patients could either re-integrate stage 2 or 3 for daily monitoring until full recovery. Out of the 305 patients included in this system, with a total of 2068 calls between March 23rd and May 29th. Seventy five were included for home hospitalization. Mean age was 36 years old [±9], sex ratio was 45/30 (female/male), mean homecare follow up was 6 days (±3), 16 patients also had Covid-19. Thirteen patients (17.3%) were hospitalized: one for an acute chest syndrome, two for a Covid-19 infection and nine for VOC management. Only one patient was in ICU due to a salmonella septicemia. No death was reported. PERSPECTIVES The Covid-19 pandemic has highlighted the need for profound reshaping of healthcare systems worldwide. In this particular context, the structure we have installed, DREPADOM, allowed follow up and monitoring of two profiles of patients: at-risk population of SCD patients and Covid-19 positive SCD patients. With the ongoing situation, our delocalized hospitalization system has proven interesting enough to enter a new phase: DREPADOM was selected as part of a public call for tenders, for financial support to make the structure permanent (DREPADOM - APRES). Disclosures Habibi: Pfizer: Consultancy; Bluebird: Consultancy; Addmedica: Consultancy; Novartis: Consultancy. Bartolucci:GBT: Consultancy; Roche: Consultancy; Emmaus: Consultancy; Innovhem: Other; Addmedica: Research Funding; HEMANEXT: Consultancy; Novartis: Consultancy; ADDMEDICA: Consultancy; Fabre Foundation: Research Funding; Novartis: Research Funding; Bluebird: Consultancy; AGIOS: Consultancy; Bluebird: Research Funding.