Suppressed CIA in CCR9-deficient mice. (A-C) CCR9-deficient mice (knockout (KO)) (n =13) and WT mice (n =16) were immunized with chicken CII on day -21 and 0. Day 0 means the day of the second immunization. Disease severity was recorded as the clinical arthritis score until day 18 (A). Ankle joints on day 18 from KO (B(i)) and WT mice (B(ii)) were stained with hematoxylin and eosin. Bar, 300 μm. Inflammatory cell infiltration in the right ankle joint was scored with a pathological score (B(iii)). Representative radiographs of the ankle joints of KO (C(i)) and WT mice (C(ii)). Bone erosion in the bilateral ankle joints was scored with radiological score (C(iii)). Representative photomicrographs are shown. Values are the mean ± SEM of each group. *P <0.05 versus WT. CCR, CC chemokine receptor; CIA, collagen-induced arthritis; CII, type II collagen; SEM, standard error of the mean; WT, wild-type.