The Impact Of CD200 Receptor On CD4+T Cell Mediated Autoimmune Colitis

Background and AimInflammatory bowel disease is a complex,systemic and chronic inflammatory disorder affecting gastrointestinal tract comprising two major types,ulcerative colitis and Crohn’s disease.Yet the etiology of IBD is not fully understood,susceptibility gene,enviromental impacts,microbiota imbalance,membrane defects and immune response are thought to be the pathogenic factors.Gene defects or chemical factors disrupt the mucosal barrier,the immune system is over-activated by the stimulation of microbiota and other factors.Among these factors,adaptive immune system disorder especially aggressive CD4+T cells have been demonstrated to play the crucial role in the pathogenesis of IBD both mice and humans.CD200 is a type I membrane protein expressed in a variety of normal epithelial cells and lymphocytes including B lymphocytes and activated T cells.CD200R,the cognate ligand for CD200,has been reported to be strongly expressed on myeloid cells such as macrophages,neutrophils and some subsets of T cells.Ligation of CD200R is thought to have negative immunoregulation function on myeloid cells.However,recent studies about the impacts of CD200R on T cells are controversial.Therefore we carried out this study to explore the impact of CD200R on CD4+T cells in IBD,which offering new immune target for clinical therapy.Methods(1)We generated CD200R gene knock out(CD200R-/-)mice.Spleen,lung,liver,colon and mensenteric lymph nodes were isolated for preparing single cell suspension.The expression of CD200R on immune cells of different organs were analysed by flow cytometry.(2)CD4+CD45RBhigh T cells were isolated from spleens and lymph nodes of donor mice(WT or CD200R-/-)by FACS sorting.Recipient mice were injected CD4+CD45RBhigh T cells intraperitoneally to induce autoimmune colitis.By comparing clinical scores,histopathologic scores and cytokine levels,we studied the effects of CD200R on autoimmune colitis in mice.(3)Using flow cytometry to analyse the expression of co-inhibitory molecules on CD4+T cells including LAG-3,CTLA-4,TIM-3 and PD-1,we explored the immunoregulation impacts of CD200R on CD4+T cells.(4)Using flow cytometry to analyse the Ki67 and 7-AAD levels on CD4+T cells.Furthermore,CD4+T cells were purified from spleens and lymph nodes of donor mice(WT or CD200R-/-)by MACS sorting,labelled with CFSE,then injected intraperitoneally into immune deficient recipient mice.5 days later,mice were sacrificed and CD4+T cells were isolated to analyse the CFSE dilution and level of 7AAD.This step was aimed to study the influence of CD200R on CD4+T cells proliferation and apoptosis.Results and Conclusion(1)CD4+T cells expressed higher amounts of CD200R than CD8+T cells in steady mice in lymphoid organs such as mensenteric lymph nodes.Besides,the levels of CD200R expression were different among CD4+subsets,such as that CD200R expression were higher on effector and Tregs compared to na?ve cells.(2)CD200 receptor defect T cells failed to induce autoimmune colitis in mice manifested as lower CD4+T cell numbers and proinflammatory cytokine levels.(3)In mice colitis models,CD200R deficiency could induce CD4+T cells express higher levels of co-inhibitory receptors including Tim-3,and CTLA-4.(4)CD200R deficiency promoted CD4+T cells division at early stage but also induced CD4+T cells to undergo accelerated apoptosis.Accordingly,CD200R deficiency induce CD4+T cells immunosupression in T cell mediated colitis through pleiotropic inhibitory pathways.Thus,our study may provide a rationale for IBD immunotherapy by targeting this receptor.