TIM-4 mediated phagocytosis of apoptotic cells induces regulatory cytokine secretion by mouse peritoneal macrophages (136.47)

Abstract TIM-4 is a member of the T cell immunoglobubulin mucin (TIM) family and is expressed on macrophage and dendritic cell populations. TIM-4 specifically binds phosphatidylserine (PtdSer) on the surface of apoptotic cells and mediates phagocytosis of apoptotic cells by macrophages. NIH3T3 cells transfected with TIM-4 can phagocytose apoptotic thymocytes and this phagocytosis can be blocked by PtdSer liposomes, indicating that TIM-4 is sufficient to mediate phagocytosis of apoptotic cells in a PtdSer-dependent manner. We examined cytokine secretion by mouse peritoneal macrophage after phagocytosis of apoptotic thymocytes and found that production of a set of cytokines including TGF-β, IL-10, and others was increased dramatically. We performed qRT-PCR assays to detect the mRNA level of these cytokines upon peritoneal macrophage phagocytosis of apoptotic thymocytes. We found that the increased cytokine mRNA levels peaked from 30 minutes to 3 hours and protein production peaked at 24h. The anti-mouse TIM-4 antibody, 21H12, can block TIM-4 recognition of PtdSer and reduce phagocytosis of apoptotic cells by peritoneal macrophages. The 21H12 antibody effectively suppressed the cytokine mRNAs induced by TIM-4-mediated phagocytosis of apoptotic cells. These findings indicate that TIM-4 plays an important role in phagocytosis of apoptotic cells and secretion of regulatory cytokines by mouse peritoneal macrophages and may play an important role in immune regulation through these cytokines.