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Rheumatoid arthritis (RA) is a chronic disease characterized by synovial inflammation and joint damage. Although both T cells and B cells mediate the disease pathogenesis, proinflammatory cytokines are critically involved. The TNF superfamiiy member B cell-activating factor (BAFF) plays an important role in humoral immunity and in autoimmune diseases, including RA. Here, we show that intra-articular injection of lentivirus expressing shRNA for BAFF gene silencing provides long-term suppression of arthritic development in a collagen-induced arthritis model. Local BAFF gene targeting inhibited proinflammatory cytokine expression, suppressed generation of plasma cells and Th17 cells, and markedly ameliorated joint pathology. Lentivirus targets dendritic cells in the joint tissue and BAFF gene silencing inhibits dendritic cell maturation and their function in driving Th17-cell differentiation in vitro. Moreover, we revealed a previously unrecognized role for BAFF in promoting the expansion of Th17 cells and demonstrated IL-17 as a crucial effector cytokine for BAFF-mediated proinflammatory effects during collagen-induced arthritis development. Taken together, these findings identify BAFF as a valuable gene-silencing target potentially for the effective treatment of RA.

Small RNAs triggering RNA silencing are loaded onto Argonautes and then sequence-specifically guide them to target transcripts. Epitope-tagged human Argonautes (hAgo1, hAgo2, hAgo3, and hAgo4) are associated with siRNAs and miRNAs, but only epitope-tagged hAgo2 has been shown to have Slicer activity. Contrarily, how endogenous hAgos behave with respect to small RNA association and target RNA destruction has remained unclear. Here, we produced monodonal antibodies for individual hAgos. High-throughput pyrosequencing revealed that immunopurified endogenous hAgo2 and hAgo3 associated mostly with miRNAs. Endogenous hAgo3 did not show Slicer function but localized in P-bodies, suggesting that hAgo3 endogenously expressed is, like hAgo2, involved in the miRNA pathway but antagonizes the RNAi activity of hAgo2. Sequence variations of miRNAs were found at both 5' and 3' ends, suggesting that multiple mature miRNAs containing different 'seed' sequences can arise from one miRNA precursor. The hAgo antibodies we raised are valuable tools for ascertaining the functional behavior of endogenous Argonautes and miRNAs in RNA silencing. Jurkat | siRNAs | Slicer