Incidence and severity of collagen-induced arthritis (CIA) in mice treated with 1-methyl-tryptophan (1-MT) or vehicle. Arthritis was first detected on day 26 after immunization with type II collagen on days 0, 21, and 42 (solid arrows) in mice treated with 1-MT or vehicle (open arrows). (a) Incidence of CIA expressed as the percentage of arthritic animals. (b) Disease severity expressed as the cumulative arthritis score in affected animals. Statistically significant differences in arthritis scores were found between days 37 and 47 (p < 0.05). Values are presented as the mean and standard error of the mean of 25 1-MT-treated and 20 vehicle-treated DBA/1 mice per group and represent two independent experiments.