Inhibition of ST2, respectively IL-1R signaling with blocking antibody. (A, C) Incidence and (B, D) severity of K/BxN serum transfer-induced arthritis are shown for WT C57BL/6 mice treated with blocking anti-ST2 antibody (n = 10, black line), blocking anti-IL-1R1 antibody (n = 10, gray dashed line) or isotype control antibody (n = 10, black dashed line) in two independent experiments (A, B: experiment 1; C, D: experiment 2). Incidence of arthritis was markedly reduced (A, P < 0.01; C, P < 0.001, longitudinal model for binomial data) in anti-IL-1R1-treated, as compared to anti-ST2 or isotype control antibody-treated mice. (B, D) Arthritis severity scores are shown as the mean ± SEM for each group of mice. The evolution of arthritis severity scores (B, P < 0.001; D, P < 0.001, mixed model for repeated measures) and disease severity at the end of the experiment were significantly reduced in anti-IL-1R1 antibody-treated, as compared to anti-ST2 or isotype control antibody-treated mice (*P < 0.01 anti-IL-1R1 vs. isotype-control; &P < 0.01 anti-IL-1R1 vs. anti-ST2). Incidence and severity of arthritis were similar in anti-ST2 and isotype control antibody-treated mice in both experiments. WT, wild-type.