The development of collagen-induced arthritis induced with type II collagen (CII) and incomplete Freund's adjuvant (IFA) in RP105-deficient mice. RP105+/+ (n = 18, 11 males and 7 females) and RP105-/- (n = 22, 11 males and 11 females) mice were immunized with CII and IFA on days 0 and 21, and signs of arthritis were monitored. The arthritis incidence was shown as per body (a) and per paw (100 × [number of the arthritic paws/number of total paws]) (b). The incidence of arthritis in RP105-/- mice was higher than that in RP105+/+ mice on days 42, 66, and 73 (a) as was the per-paw incidence after day 38 (b). (*P < 0.05, **P < 0.01, and ***P < 0.001 for comparison with RP105+/+ mice, chi-square test) (c, d) The disease severity, expressed as the mean arthritis index (and standard error) of total mice (c) and of arthritic mice (d), is shown (*P < 0.05 and **P < 0.01 for comparison with RP105+/+ mice, Mann-Whitney U test).