CD97 monoclonal antibody (mAb) treatment ameliorates arthritis activity in a dose-dependent manner. Mice were treated with NaCl (■), 0.5 mg control immunoglobulin (cIg) (•), or 0.25 mg (○) or 0.5 mg (□) anti-CD97 mAb. Delta arthritis scores were calculated by subtracting the score at the day of initiation of treatment from the measured score. Values are mean ± standard error of the mean. Areas under the curve (AUCs) were calculated for the delta clinical scores of each mouse. Experiment 1 (a,b) was performed to find an effective dosage of the CD97 mAb. Mice were treated from day 21 on (n = eight mice per group). In experiments 2 and 3, the effect of treatment in early (c,d) and longstanding (e,f) disease was studied. Treatment was started from day 21 (eight mice per group) or day 35 (20 mice per group) on, respectively. *P < 0.05.