CCRL2-deficient mice are protected in experimental inflammatory arthritis. (A) Clinical score of CIA in DBA1 mice treated 3 times per week with anti-CCRL2 or isotype control antibody (Iso Ctr) (100 μg per mouse intraperitoneally) starting the day before the first immunization with bovine type II collagen. One representative experiment of 2 is shown. ***P < .001 for DBA1+anti-CCRL2 vs DBA1+Iso Ctr by two-way ANOVA (n = 10 per group). (B) Clinical score of STIA determined in CCRL2 KO, WT, and anti-CCRL2 antibody–treated WT mice (anti-CCRL2) (100 μg per mouse from day 0 to day 4). STIA was induced by injection of 150 μL of K/BxN serum at day 0 (n = 5 per group). Clinical score was assessed daily. One representative experiment of 3 is shown. ***P < .001 for WT vs CCRL2 KO or anti-CCRL2 group by two-way ANOVA. (C) For Ly6G staining, hyaluronidase-treated tissue sections were stained with a rat anti-mouse Ly6G antibody (BD Biosciences). Left panel: quantitative analysis of immunohistochemical staining for Ly6G⁺ cells per mm² of joint sections scanned by VS120 Dot-Slide BX61 virtual slide microscope (Olympus Optical) and analyzed by using Image Pro-Premiere software (Media Cybernetics). *P < .05; **P < .01 by one-way ANOVA (n = 6 mice per group). Right panel: representative images of Ly6G staining of arthritic joints from WT, anti-CCRL2 moAb–treated WT, and CCRL2 KO mice (original magnification 10×; insets 20×). (D) Circulating levels of interleukin-6 (IL-6), CXCL1, CXCL2, CCL5, and chemerin in sera of WT and CCRL2-deficient mice at day +4 of STIA by Luminex Multiplex assay. (E) Clinical score of WT or CCRL2 KO mice receiving BM neutrophils (polymorphonuclear leukocytes [PMNs]; 5 × 10⁶ per mouse per day) from WT and CCRL2 KO mice in STIA model. Data (n = 5 per group) from 1 representative experiment of 3 are shown. *P < .05 for PMN WT in WT mice or PMN WT in KO mice, or PMN KO in WT mice vs PMN KO in KO mice by two-way ANOVA.