Perforin-deficient (pfp-/-) mice develop decreased collagen-induced arthritis (CIA). Percentage of CIA-affected animals (a) is decreased and average maximum score (b) is significantly lower in pfp-/- mice than in pfp+/- and pfp+/+ mice. Figures show results from two different experiments, with balanced groups, taken together. Maxscore was calculated as the mean maximum score for each individual mouse of a given genotype. *P < 0.05.