Antibody response and T cell proliferation. (a) No significant variations in the levels of collagen-specific IgG antibodies between the perforin (pfp)-deficient mice (n = 6) and the control littermates (pfp+/- and pfp+/+; n = 10) were seen. Sera were obtained from the mice 21 days after immunization with collagen type II (CII) and complete Freund's adjuvant (CFA). Levels of collagen-specific IgG antibodies were measured by quantitative ELISA. (b) pfp-/- mice show an increased proliferation toward CII. Draining lymph nodes were obtained from pfp-/- (n = 3) and pfp+/+ (n = 3) mice 90 days after immunization with CII in CFA. The cells were cultured for 60 hours with collagen II in different concentrations, and then pulsed with [3H]thymidine. *P < 0.05.