Statistics.

Mouse group sizes were determined by an a priori power analysis for a 2-tailed, 2-sample t test with an α of 0.05 and power of 0.8, in order to detect a 20% difference in arthritis scoring at the age of 16 weeks. Animals were randomized during the experiments. Both sex mice were used for all the experiments, and no samples or animals were excluded from analysis. The data in the graphs were analyzed for statistical significance with 2-tailed Student’s t test and 2-way ANOVA and Tukey’s multiple comparison test, as well as with 1-way ANOVA. Bonferroni’s multiple comparison tests were used to analyze groups for statistical significance. Such comparisons and the resulted P values are always depicted in the figure and figure legends depending of the experiment. In each case, P < 0.05 were considered significant. Statistical analyses in this study were performed using GraphPad Prism6 software (version 6.01). Biostatistical analysis is described in a separate section in Supplementary Material.