Investigation On The Roles Of CD4~+T Cells In Generation Of Pathogenic Antibodies In Systemic Lupus Erythematosus And Relevant Mechanisms

Systemic lupus erythematosus（SLE）is a severe heterogeneous systemic autoimmune disease characterized by the dysfunction of immune system.The main pathological characteristics are the production of multiple autoantibodies and the formation of immune complexes deposited in multiple tissues and organs,resulting in pathological damages.The pathogenesis of SLE is complex.Many studies have shown that T cell dysfunction exists in SLE patients and may play an important role in the production of autoantibodies.In this study,pristane-induced lupus mouse model was used to detect the production of pathological antibodies and the activation of CD4⁺T cells by ELISA and flow cytometry（FCM）respectively.The effects of CD4⁺T cells from lupus mice on the production of pathological antibodies and the related mechanisms were studied by in vitro T-B cells co-culture.Our results showed that pristane-induced BALB/c mouse model showed a series of pathological changes similar to SLE,including high expression of autoantibody,abnormal activation of B cells,lupus-like pathological damage in the kidneys and the joints of mice,as well as significantly increased proportion of CD11b⁺Ly6C^high cells in peritoneal cavity.By using this pathological model,it was further found that the expression levels of CD4⁺T cell surface related to the activation including CD44,OX40,ICOS,ICAM-1,PD-1 and CTLA-4 were higher in pristane-treated mice than those in PBS control group.We also found that the percentages of IL-17 and IL-10 secreting CD4⁺T cells in pristane treated group were higher than that in PBS treated group,while the expression of IFN-γin CD4⁺T cells from pristane treated group was lower than those from PBS treated group.These results indicated that the percentage of Th1 CD4⁺T cells decreased in pristane-induced lupus-like mice,while the proportion of inflammatory-related Th17 and Th2 cells increased.In order to analyze the effects of CD4⁺T cells from lupus-like mice on the production of pathological antibodies,CD4⁺T and B cells sorted from pristane or PBS treated mice were cross-cultured in vitro and the antibodies in culture supernatant were detected by ELISA.The results showed that CD4⁺T cells from pristane-treated mice promoted B cells to produce more IgM and IgG than those from PBS group,suggesting the roles of CD4⁺T cells in the lupus-like mice in promoting the production of antibodies.ICAM-1 is an adhesion molecule.Its roles in T-B cell interactions remain unclear.To determine the effects of ICAM-1 on antibody production,CD4⁺T and B cells from pristane treated mice were co-cultured with neutralizing anti-ICAM-1 Ab or control isotype-matched Ab in vitro.Results from ELISA analysis showed that the IgG level increased while the IgM level decreased in the culture supernatants from the group treated with anti-ICAM-1 Ab as compared with control group.These results suggest that the ICAM-1 signaling pathway may not be conducive to the IgM-to-IgG switch,which providing a new theoretical basis for the molecular mechanism of ICAM-1 involved in antibody class switch in systemic lupus erythematosus.Taken together,in this study our results show that CD4⁺T cells in pristane-treated mice are activated and play important roles in the production of pathological autoantibodies.In vitro assay demonstrats that the ICAM-1 signaling pathway might be involved in the progress of IgM-to-IgG switch,which is critical in the induction of pathological autoantibodies in pristane-induced lupus mice.Our study herein provides new molecular signatures for clinical diagnosis and the treatment of SLE.