CD72 Downregulation on CD5+ B Cells Promotes CD5-associated B Cell Proliferation and IL-10 expression during HBV Infection

Abstract Backgroud: B cells play an important role in HBV infection. CD72 is expressed on B cells, and negatively regulates B cell activation. And the effects of CD72 on B cell proliferation associated with CD5 expression have not yet been studied. The aim was to assess the impact of CD72 expression on CD5+ B cells during HBV infection. Method: Peripheral blood mononuclear cells with HBV infection and healthy donors were collected, and CD72 on B cells were examined. The correlation between CD72 and CD5 expression on B cells was analysed by flow cytometry. The effect of CD72 expression on signal transduction and B cell proliferation were assessed by western blotting and BrdU assays. Results: CD72 expression was significantly lower on CD5+ B cells of patients with HBV infection than those of healthy donors (P < 0.001). A negative correlation was found between CD72 and CD5 expression on B cells (P <0.01 in cells%; P = 0.033, in mean fluorescence intensity). CD5+ B cell proliferation was significantly increased after CD72 suppression. CD5+ B cell proliferation was associated with ERK and Syk activation in patients with HBV infection. And the CD72 downregulation in CD5+ B cell induced IL-10 upregulation. Conclusion: CD72 expression was downregulated in CD5+ B cells of patients with HBV infection. Downregulation of CD72 in CD5+ B cells promotes CD5-associated B cell proliferation and IL-10 expression in an ERK and Syk signalling-dependent manner.