Comparison of the development of spontaneous arthritis in male DBA/1 and DBA/2 mice. Cumulative incidence (A) and clinical severity (B) of arthritis in male DBA/1 and DBA/2 mice. (B) Data are shown as mean + SEM; n = 15 or 12 mice per group. (C) Representative microscopic image of late stage endochondral bone formation in an arthritic DBA/2 hind paw. C’ shows a higher magnification of boxed area in C. Scale bars: 500 μm in C, 125 μm in C’.