Groups of 4-mo-old naive male B10.RIII mice were injected i.v. with 9 mg of a single mAb or an equal combination of two mAbs. M2139 with CIIC1 and 4.5 mg M2139 with PBS constituted positive and negative controls, respectively. 25 µg LPS per mouse was injected i.p. on day 5 to enhance the incidence and severity of arthritis. Cumulative incidence: M2139 + ACC4 versus M2139 + PBS, P ≤ 0.0006; and ACC1 versus ACC4, P < 0.001. Maximum arthritis score: M2139 + ACC4 versus M2139 + PBS, P < 0.0001; and ACC1 versus ACC4, P = 0.0024. Results shown are pooled values from three similar experiments. **, P < 0.005; ***, P < 0.001; and ****, P < 0.0001.