Experimental design. Eight-week-old male DBA1/J mice were divided into 4 groups (6 in each), i.e., RA-/Ab-, RA-/Ab+, RA+/Ab-, and RA+/Ab+. A cocktail of anti-type II collagen antibodies and E. coli LPS was injected intra-peritoneally into the RA+ mice on days 0 and 3, respectively. RA- mice were the control without injection of the anti-type II collagen antibodies and LPS. The OYC1 anti-RANKL monoclonal antibody (5 mg/kg) was injected subcutaneously into the Ab+ mice on day 5. Ab- mice were the control without injection the anti-RANKL antibody. Arthritis scores were determined daily from day 0 to 14. The 4 limbs were removed on day 14 for analysis of histological changes in the joints.