To block the TLR9 expression in vivo, 6- to 8-week-old female BALB/c mice were randomized to inject with TLR9 specific siRNA or control siRNA using in vivo-jetPEI every other 3 days for 6 weeks.

We previously established a systemic lupus erythematosus (SLE) animal model in non-susceptible BALB/c mice by immunizing with activated syngeneic lymphocyte-derived DNA (ALD-DNA), manifested by high level of anti-double-stranded DNA (dsDNA) antibodies (Abs), proteinuria, glomerular deposition of immune complex and glomerulonephritis. The production of anti-dsDNA Abs is closely related with the renal inflammation and damage in this model. However, recognition of ALD-DNA and its signaling pathway within antigen-presenting cells (APC) remains not fully clarified. Herein, in this study, Toll-like receptor 9 (TLR9), a well-known pattern-recognition receptor for dsDNA with CpG motif, was found to be dynamically up-regulated in B cells during the process of the SLE disease. Knockdown of TLR9 by short interfering RNA (siRNA) in B cells in vitro and in vivo reduced the production of anti-dsDNA antibody and consequently ameliorated the SLE syndrome in mice while the affinity and isotype of the antibody remained the same. Our results implied that TLR9 signaling of B cells might play an important role in the production of anti-dsDNA Abs triggered by auto dsDNA, which would extend our understanding of TLR9 immune recognition in the pathogenesis of SLE disease.