The development of collagen-induced arthritis in RP105-deficient mice. (a-d) RP105+/+ (n = 26, 13 males and 13 females) and RP105-/- (n = 27, 13 males and 14 females) mice were immunized with type II collagen (CII), and signs of arthritis were monitored as described in Materials and methods. The incidence of arthritis in RP105-/- mice was higher than that in RP105+/+ mice between days 31 and 42 (*P < 0.05 and **P < 0.01 for comparison with RP105+/+ mice, chi-square test) (a). The disease severity, expressed as the mean arthritis index (and standard error) of the total mice (b) and of the arthritic mice (c), is shown (*P < 0.05 and **P < 0.01 for comparison with RP105+/+ mice, Mann-Whitney U test). (d) A histological examination was performed in RP105+/+ (n = 20, 10 males and 10 females) and RP105-/- (n = 23, 11 males and 12 females) mice at day 35 (*P < 0.05, chi-square test). (e) The anti-CII antibodies of IgG1 and IgG2a classes were measured from RP105+/+ (n = 18) and RP105-/- (n = 19) mice on days 28 and 42. Values are mean ± standard error (*P < 0.001, Wilcoxon matched pairs test). AU, arbitrary units.