PG-specific antibody isotypes and cytokines in PG-induced arthritis. (a) Serum concentrations of PG-specific IgG1 and IgG2a isotypes and production of PG-specific cytokines by spleen cells of PG-immunized mice. PG-specific (anti-human and anti-mouse) isotypes were measured in sera (N = 30) and cytokines in supernatants of spleen cells (N = 5). (b) T-cell-deficient (nude) and CD40-deficient mice did not generate a PG-specific antibody response. Heterozygous and homozygous nude and CD40-deficient mice were immunized with PG. Note: Scales for antibody concentrations differ between panels A and B. Values are means; whiskers indicate SEM. h, m = respectively, antibodies to human and mouse PG; PG = proteoglycan. *P < 0.05 in comparison with heterozygous nude mice.