CD200 Role In The Clearance Of Apoptotic Cells

BackgroundSystemic lupus erythematosus (SLE) is an autoimmune disease of unclear etiology that affects multiple organs. Plethora of data demonstrates that aberration of apoptosis and disturbed clearance of apoptotic cells are involved in the pathogenesis of SLE. CD200is a trans-membrane glycoprotein which is expressed on a variety of cells and its binding with CD200R plays an immunoregulatory role. Recently, preliminary study has shown that surface CD200expression is increased during apoptosis and a different CD200/CD200R expression pattern and an increased apoptotic ratio is also observed in SLE patients, which indicates a possible aberration in CD200/CD200R pathway in SLE patients. This thesis mainly investigates the role of CD200in dendritic cell’s engulfment process during apoptotic clearance.Methods1. CD200+/CD200-live cells, CD200+/CD200-early apoptotic cells and CD200+late apoptotic cells were sorted by flow cytometer and then cocultured with autologous dendritic cells in vitro. Contact and phagocytic ratios were compared between different groups using Fluorescence Microscope and Flow Cytometer.2. The supernatant CD200concentration of apoptotic cell and live cell is measured by Enzyme-linked Immunosorbent Assay (ELISA). Clinical data was collected, including SLEDAI, anti-dsDNA tilter, C3, ESR, WBC and lymphocyte count, and correlation analysis with CD200supernatant concentration was done.3. Transwell migration assay was done to investigate the role of CD200in dendritic cells’chemotactic ability.Results1. In coculture experiment, the contact ratio and phagocytic ratio with dendritic cell is lower in CD200+cells, compared with CD200-cells. With the progress of apoptosis, the contact ratio and phagocytic ratio are increased. The SLE patients have a seemingly lower contact ratio compared with HC.2. In HC, CD200concentration of apoptotic culture supernatant is higher than that of living culture according to ELISA results. In SLE patients, supernatant CD200concentration of living culture is positively correlated with ESR, while CD200of apoptotic culture is negatively correlated with C3and WBC. 3. In transwell migration assay, CD200is a negative chemo attractant for both immature and mature dendritic cells.ConclusionTo sum up, during the apoptosis, the supernatant CD200concentration is increased as well as the the surface CD200expression. In the process of apoptotic cell clearance, soluble CD200acts as a "don’t find me" signal, which is a negatively chemo attractant for DC while membrane CD200serves as a "don’t eat me" signal to inhibit DCs’ phagocytosis.