Histopathology of perforin-deficient pfp-/- mice compared with pfp+/- mice. (a) Joint of a pfp-/- mouse with severe inflammation and erosions, stage 4. (b) Paw of a heterozygous mouse in the same stage of disease. (c) Comparison of histological and clinical evaluation of the disease. Data are values of severity of pfp+/- mice (n = 6) and pfp-/- mice (n = 6), and are shown as means ± SEM.