Delayed development and progression of collagen-induced arthritis in DBA/1 mice subjected to prolonged cigarette smoke exposure. (a) Clinical signs of arthritis were followed between days 21 and 46 after immunization. Statistical evaluation was performed using chi-squared test. Development of arthritis was significantly delayed in smoking animals (P < 0.05). (b) Weight development after immunization with collagen II. Weight change was calculated as the change in percent as compared with the day of booster injection with collagen II. (c) Histologic changes in the joints were evaluated at day 46. (d) Levels of IL-6 were measured in serum at day 46 after first immunization. (b to d) Statistical evaluation was made using Mann-Whitney U test. Values are presented as mean ± standard error of the mean. Horizontal lines indicate medians. Data from two independent experiments were pooled (n = 50).