CCRL2-deficient mice are protected in CIA. (A) Clinical score of CIA in WT and CCRL2-deficient (KO) mice immunized with chicken type II collagen. Scores from 4 paws were combined for each mouse, and total severity score for the group was divided by the number of arthritic mice to obtain an average severity score (clinical score, 0-16 in the 4 paws). Data are shown as mean ± SEM from 1 representative experiment of 3 (WT, n = 29; CCRL2 KO, n = 24). (B) Histopathology of a representative arthritic joint from WT and CCRL2 KO mice (original magnification 4×). (C) Histopathologic score of arthritic mice as evaluated for leukocyte infiltration, erosion, pannus, necrosis/fibrosis, loss of cartilage, and bone integrity. Data are shown as mean ± SEM of arthritic scores of 1 representative experiment (WT, n = 8; CCRL2 KO, n = 10). (D) Levels of total anti-collagen II immunoglobulin G (IgG) (μg/mL) measured in mouse sera at the end of the experiment (day +60). **P < .01 by Mann-Whitney U test; ***P < .001 for WT vs CCRL2 KO mice by two-way analysis of variance (ANOVA).