Role of pathogenic auto-antibody production by Toll-like receptor 9 of B cells in active systemic lupus erythematosus

Objectives. Toll-like receptor 9 (TLR9) is a pattern-associated receptor functioning in innate immunity that may be involved in the recognition of self-antigens and the production of pathogenic auto-antibodies. Therefore, we examined the expression of TLR9 in systemic lupus erythematosus (SLE) to determine whether TLR9 is involved in the production of pathogenic auto-antibodies. Methods. B cells were collected from patients with active SLE, and subjected to analysis of the TLR9 molecule using flow cytometry fluorescence activated cell sorting (FACS) and TLR9 mRNA by reverse-transcriptase polymerase chain reaction. SLE B cells were stimulated with CpG-ODN, and subsequent cytokine and anti-dsDNA antibody production was measured by enzyme-linked immunosorbent assay. Results. The expression and mRNA level of TLR9 on B cells was up-regulated in SLE patients, and SLE disease activity index (SLEDAI) and CH50 were correlated with TLR9 expression on CD20þ B cells. Moreover, TLR9–CpG interaction enhanced the production of anti-dsDNA antibody and IL-10. Conclusions. The present study demonstrated that higher expression of TLR9 on peripheral blood B cells from patients with active SLE was significantly correlated with CH50 and SLEDAI to TLR9, and induced the production of anti-dsDNA antibody and IL-10 by TLR9–CpG ligation. These results suggest that an abnormality of innate immunity plays a crucial role in the pathology of SLE, and that blockade of CpG–TLR9 interaction may be a new therapeutic approach for SLE