Humoral immune responses in chimeric CD40 transgenic mice. Mice were immunized with 100 μg NP₃₀-KLH emulsified in CFA. Circulating antibodies were measured by an NP-specific, isotype-specific ELISA. (A) Both total NP-specific IgG1 (NP30) and high-affinity NP-specific IgG1 (NP4) responses from different chimeric CD40 transgenic mice were followed over time (days 14, 28, 42, and 56) (*P < .05 by analysis of variance versus values for CD40^−/− at indicated time points). (B) The alterations of IgG1 responses (total versus high affinity) to NP antigen in Δ260 mice over time were shown. Data represent 2 independent experiments (mean ± SD).