TLR9 and BAFF: Their expression in patients with IgA nephropathy

Since it was first described in 1968, immunoglobulin (Ig)A nephropathy (IgAN) has become the most commonly diagnosed form of primary glomerular disease worldwide. A number of reports have shown that toll-like receptor 9 (TLR9) and B-cell activating factor (BAFF) may be associated with IgAN; however, sufficient evidence has not yet to be delivered. In the present study, serum levels of BAFF as well as TLR9 mRNA and protein levels in peripheral blood mononuclear cells (PBMCs) were assessed. Expression of TLR9 mRNA in PBMCs was examined by quantitative polymerase chain reaction and the TLR9 protein was determined by western blot analysis. The levels of serum BAFF and IgA1 were determined by specific ELISA. Serum levels of BAFF and IgA1 as well as levels of TLR9 mRNA and protein in PMBCs were significantly higher in patients with IgAN compared with patients with minimal glomerular abnormalities (P<0.05, P<0.01, P<0.01 and P<0.01, respectively) and normal controls (P<0.01, P<0.01, P<0.05 and P<0.01, respectively). A correlation and regression analysis was performed to determine the pathogenesis of IgAN. In patients with IgAN, serum levels of BAFF were positively correlated with IgA1 levels (rp, 0.515; P<0.01) and mesangial IgA deposition density (rp, 0.746; P<0.01). Expression levels of TLR9 protein in PBMCs of IgAN patients were positively correlated with levels of serum BAFF (rp, 0.444; P<0.05) and IgA1 (rp, 0.633; P<0.01). These results suggested that overexpression of TLR9 mRNA and protein in PBMCs and elevated levels of serum BAFF may be associated with over-expression of serum IgA1, and, furthermore, may have a role in the development of IgAN.