(A) Purified D513, 1042, or 1618 monoclonal antibody was applied to a Western blot of unmodified and citrullinated fibrinogen. To compete for antigen binding on the blot, soluble unmodified or citrullinated fibrinogen was added to D513 prior to applying the antibody to the Western blot. (B) The relative reactivities of the monoclonal antibodies for unmodified and citrullinated fibrinogen were determined by applying increasing amounts of biotinylated unmodified and citrullinated fibrinogen (fibr) and CII to ELISA plates coated with monoclonal antibody. The amount of protein binding was detected as described in Methods and is displayed as OD. (C) Additional antigens recognized by D513, 1042, and 1618 were detected using synovial antigen arrays. The relative reactivity for the antigens recognized is shown. (D) Arthrogen, a cocktail of 4 monoclonal antibodies against CII, was transferred intravenously into 6- to 8-week-old male DBA/1J mice at increasing doses followed by 50 μg LPS intraperitoneally 3 days later in order to determine which dose would establish submaximal disease. n = 3 per dose group. (E) D513 (n = 9) or control monoclonal antibody (n = 6) were administered alone or in combination with the submaximal dose of Arthrogen (1 mg). (F and G) Either 1 mg or 2 mg of monoclonal antibody 1042 or 1618 (n = 6) or 2 mg HB5 control monoclonal antibody (n = 6) was combined with 1 mg of Arthrogen and transferred into mice as performed previously with D513. Data shown are the average disease score per group α SEM. Statistical significance was determined using 1-way ANOVA. *P < 0.05; **P < 0.01 in comparison with submaximal Arrogen alone.