Production of PG-specific IgG2a isotype is increased in IL-4-deficient mice. Wild-type, IL-4-deficient, and IFN-γ-deficient mice were immunized with PG, and serum antibody isotypes to human PG (a) or mouse PG (b) were measured by ELISA. Values are means; whiskers indicate SEM. PG = proteoglycan; WT = wild-type. *P < 0.05 in comparison with wild-type mice.