Spontaneous arthritis in KRN/I-Ag7 mice with or without TRAF1. One hundred percent of KRN/I-Ag7 mice with or without TRAF1 developed spontaneous arthritis. a–c: Representative images of right hind paws of 1.5-month-old TRAF1-deficient B6.I-Ag7(a), B6.KRN/I-Ag7(b), and TRAF1-deficient B6.KRN/I-Ag7(c) mice. d-i: Cohorts (N = 8–10) of female (d, f, h) and male (e, g, i) mice were followed for clinical arthritis between ages 3 to 10 weeks. Closed symbols represent TRAF1-sufficient mice, and open symbols represent TRAF1-deficient mice. Shown are arthritis incidence (d, e); clinical index (f, g); and ankle thickness (h, i). * Indicates that the two groups are statistically different (p < 0.05) at the given time point by Student’s T test.