Effect of bosentan on histopathological manifestations of antigen-induced arthritis (AIA). (a) Mice were killed 3 days after induction of AIA. (b) Mice were killed at day 42 after repeated induction of AIA. Affected knee joints were prepared for histological scoring. Four sections per knee joint were examined by an observer who was blinded to the treatments and were scored according to a three-parameter scoring system as described in Materials and methods. Values are means ± standard error of the mean. The results from two-way analysis of variance followed by the Bonferroni post hoc test are shown (*P < 0.05).