As no previous reports have addressed functional links between TLR4 and IL-12 regulatory axes in the pathogenesis of antibody-induced arthritis, this study provides the first demonstration that TLR4-mediated IL-12 promotes arthritis by regulating the production of both IL-1β and IFN-γ, thereby suppressing TGF-β production. Here, TGFB1 is linked to arthritic joint disease.