Irf7−/− mice have increased arthritis in the passive K/BxN serum transfer model. A. Irf7−/− mice developed significantly more paw swelling than WT controls day 8 and day 12 (left panel, *p<0.05). Total area under the curve (AUC) was significantly increased in Irf7−/− mice compared with WT (right panel, **p<0.05). Data are representative of 2 independent experiments. B. IFNβ was decreased in Irf7−/− synovial tissue. Relative expression (RE) of IFNβ, IL-6, RANTES, and MIP-1α was decreased (*p<0.05) compared with control. RE of TGFβ, IL-1RA, IP-10, MMP-3, and VEGFα was not significantly different. C. Serum IFNβ protein measured by ELISA was decreased in the Irf7−/− arthritic mice (*p<0.009, n=8 mice per group). Levels of IL-10 and IL-1RA were not different in sera of WT and Irf7−/− K/BxN mice.