Fig. 2

CII-specific IgG production was suppressed in Il21r KO mice with CIA. Levels of anti-CII IgM (a) and IgG (b) Abs in the serum of WT mice (filled circle, n = 6) or Il21r KO (open circle, n = 6) mice during the course of CIA. c Levels of anti-CII IgG1 (upper panel) and IgG2c (lower panel) Abs in the serum of WT mice (gray column, n = 6) and Il21r KO mice (open column, n = 6) at 5 weeks after CIA induction. Sera from naïve WT mice were used as the negative control (filled column, n = 6). Levels of anti-CII IgG1 and IgG2c Abs in the serum of naïve Il21r KO mice were not different from those of naïve WT mice. Error bars represent mean ± SEM. Statistical significance was analyzed by two-way ANOVA with repeated measures (a, b) or one-way ANOVA with Tukey’s multiple comparison test (c). *p < 0.05, different between WT mice and Il21r KO mice or naïve and immunized mice. Data are representative of three independent experiments. CII type II collagen, Il21r KO IL-21 receptor knockout, O.D. optical density, WT wild type