(A) B1R antagonist SSR240612 significantly reduced ZIA in WT mice compared with vehicle-treated mice. n = number of mice per group: PBS, n = 5; zymosan, n = 10; zymosan + SSR, n = 10. (B) Knee homogenates from SSR240612-treated mice showed significantly lower IL-1β and IL-6 in comparison with vehicle-treated mice. n = number of mouse knees per group: PBS, n = 3; zymosan, n = 5; zymosan + SSR, n = 5. (C) Immunofluorescence of knees from SSR240612-treated mice shows a marked decrease in macrophage marker F4/80 (green). Representative sections from each group are shown. Original magnification, ×200. (D) Vehicle-treated WT mice (n = 9–13) had profound serum transfer arthritis as measured by joint circumference compared with SSR240612-treated WT mice (n = 10). There was no difference in arthritis between SSR240612-treated Cd13–/– mice (n = 6) and vehicle-treated Cd13–/– mice (n = 10) except for day 8. (E) Significant decrease in MCP-1/CCL2 and IL-6 in ankle homogenates from SSR240612-treated WT (n = 9) compared with vehicle-treated WT mice (n = 13) is shown. In contrast, significant increase in the cytokines was observed in the SSR240612-treated Cd13–/– mice (n = 8) compared with vehicle-treated Cd13–/– mice (n = 6). (F) SSR240612-treated WT and Cd13–/– mouse cryosections showed a marked decrease in F4/80 staining compared with sections from vehicle-treated mice. Red staining represents F4/80 for MNs/macrophages, while blue (DAPI) stains nucleus. Original magnification, ×200. Results are expressed as mean ± SD. *P < 0.05. Significance was determined by Kruskal-Wallis test (A and E), 1-way ANOVA (B and F), and 2-way ANOVA (D).