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.
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.
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 CD20+ B cells. Moreover, TLR9-CpG interaction enhanced the production of anti-dsDNA antibody and IL-10.
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.