Increased let-7b-5p is associated with enhanced BAFF-R expression and B cell survival in immune thrombocytopenia

B cells play a key role in the pathogenesis of immune thrombocytopenia (ITP) by producing platelet autoantibodies. Accumulating evidence suggest that microRNA (miRNA) is a critical regulator in B cells. The contribution of miRNA to B cell dysfunction in ITP has not been described. The aim of this study was to examine the expression of miRNA let-7b-5p in B cells of ITP patients and investigate its possible association with B cell function in ITP. The CD19+ cells were isolated from peripheral mononuclear cells of ITP patients and healthy controls using immunomagnetic microbeads. B cell survival in vitro was evaluated by cell counting. The level of let-7b-5p was quantified by quantitative PCR. The surface expression of B cell activating factor receptor (BAFF-R) was detected by flow cytometry. The role of let-7b-5p was examined in isolated B cells by transfecting miRNA mimics or inhibitors. The results showed that let-7b-5p in B cells was elevated, and B cell survival was enhanced in ITP patients compared with healthy controls. BAFF and B cell receptor stimulation can induce the expression of let-7b-5p in vitro. Overexpression of let-7b-5p in B cells enhanced the expression of surface BAFF-R and promoted B cell survival. Moreover, let-7b-5p enhanced the phosphorylation of NF-κB2 p100 and upregulated the expression of survival factor Bcl-xL after BAFF induction. Let-7b-5p is a pro-survival miRNA in B cells and increased let-7b-5p is associated with enhanced surface BAFF-R in ITP.