Treatment with a monoclonal anti-IL-36 receptor (R) antibody does not modify the course of collagen-induced arthritis (CIA). CII-immunized mice (n = 10/group) were treated with anti-IL36R (M616, squares, white columns), anti-IL-1RI (M147, triangles, dashed columns) or isotype-matched control antibodies (4G8 (circles, grey columns) for M616, 4D2 (triangles, black columns) for M147), as described in Materials and methods. Results show the incidence of arthritis (A), the clinical severity of articular inflammation (B) and the number of arthritic paws (C) on days 21 to 41. The systemic inflammatory response (D) was assessed by measuring circulating IL-6 levels on day 41 after the first immunization. Joint sections from all mice were evaluated on day 41 for histological scores (E) and histological features (F). All sections were scored for inflammation, cartilage erosion and neutrophil infiltration. Images are representative of H&E- or toluidine blue-stained sections of knee joints for each group (original magnification × 10). (G) Levels of CXCL-1 (ng/mL) were determined by ELISA in ankle extracts of each mouse on day 41 and normalized by the total protein concentration (mg/mL). (B, C, E) Values are the mean ± standard error of the mean. ***P < 0.001, anti-IL-1RI versus isotype control 4D2; &P < 0.05 and &&P < 0.01, anti-IL-1RI versus anti-IL-36R, as assessed by Kruskal-Wallis test (B and C) or by analysis of variance (ANOVA), followed by unpaired two-tailed Student's t-test (E). (D, G) Results are shown as individual values for each mouse (symbols) and mean values (lines) **P < 0.01, anti-IL-1RI versus isotype control 4D2, as assessed by ANOVA, followed by unpaired two-tailed Student's t-test.