B Cells Contribute To Controlling Imiquimod-induced Psoriasis In Mice

Background:Psoriasis is a common chronic inflammatory autoimmune disease which is medicated by Thl/Th17 in dermatology.However,recent study has reported that patients with autoimmune disease occur psoriasis-like lesions by depleting B cell,which suggest that B cells may play an important negative regulation in the pathogenesis of psoriasis.Objective:To clear whether B cells are involved in psoriasis induced by imiquimod(IMQ),and to further investigate the possible mechanism by B cell deficient mice.Methods:IMQ ointment was applied on the back skin of C57BL/6 mice and B cell-dificient(μMT)mice for six consecutive days to construct mice model of psoriasis.The clinical symptom was scored based on the PASI.Erythema,scaling and thickness were scored on a scale from zero to four.On the sixth day,the pathological changes were observed through HE staining in skin lesions.Spleen and lymph nodes were taken from the mice after application of IMQ for six days,to detect the percentage and the number of CD4+T cells,CD8+T cells,CD19+B cells,CDldhiCD5+CD19+B cells,regulatory T cells and the alter of cytokines(IL-4,IFN-y,IL-17,IL-10)by flow cytometry.Lymphocyte suspension of spleen were prepared one day before or six days after IMQ induction,spleen cells were stimulated for 5 hours by LPS,ionomycin and PMA,analysis the changes of CD19+IL-10+B cells by flow cytometry.B cells in the spleen were isolated by magnetic beads and then stimulated with LPS and PMA for 24 hours,IL-10 expression in the supernatant was measured by ELISA.Results:Two or three days after the start of IMQ application,it began to appear erythema and tiny scales;After five to six days of application,the symptoms peaked which large patches of erythema,a great amount of scales and the epidermis thickened were visible.Since then,the symptoms have been gradually weakened,but the score has always been significantly higher than control group.HE staining showed severe parakeratosis,epidermal thickening,extension of spike-like protrusions and many inflammatory cells in dermal layer in experimental group.There was no abnormality in clinical scores and histopathological changes in control group.The results of flow cytometry showed that,compared with control group,the number and percentage of CD19+B and CD4+T cells in IMQ mice were declined and the ratio of CD4+/CD8+T cells was significantly decreased(P<0.05);The percentage and the number of Treg were obviously increased(P<0.001).the erythema,scales,and skin thickening of μMT mice were more severe than C57BL/6 mice(P<0.05).In comparison with C57BL/6 mice,HE staining showed a more obvious epidermal thickening,granular layer disappearance,a severe parakeratosis,a nail extension and Munro microabscesses in μMT mice.There are a lot of inflammatory cells infiltration,erythrocytes diapedesis,angiotelectasis and distortion in dermis layer;As the disease progressed,Flow cytometry showed that IL-10+B cells and CD1dhiCD5+CD19+B cells decreased significantly in C57BL/6 mice,with significant differences between the two groups.ELISA results showed that IL-10 expression by B cells in the spleen of experimental group was significantly lower than control group(P<0.01).The flow cytometry results showed that IL-10+CD4+T in the spleen of μMT mice was significantly reduced than C57BL/6 mice(P<0.05),the expression of IL-17+CD4+T,IFN-y+CD4+T and IFN-y+CD8+T cells was not significantly altered(P>0.05).The percentage of Treg cells in lymph nodes and spleen were significantly decreased,with significant differences between the two groups(P<0.05).Conclusion:B cells participate in the development of IMQ-induced psoriasis,and possibly regulate the balance of Thl/Th2 or interaction with Treg cells.