Immune responses of 129Ola × C57BL/6J F3 CD38^−/− mice (open symbols) and CD38^+/+ littermate controls (closed symbols) to TD antigens. Titers of hapten-specific IgG1 serum antibody at various time points after a primary (left), and secondary (right) immunization with 10 μg alum-precipitated TNP₅-KLH (A), 10 μg alum-precipitated NP₂₀-CG (B), or 10 μg CFA-precipitated TNP₅-KLH (C). Arrows indicate the time of the primary and secondary immunizations. The data shown are representative of one of eight TNP₅-KLH in alum immunization experiments, one of two NP₂₀-CG in alum immunization experiments, and one of three TNP₅-KLH in CFA immunization experiments, in which each experiment included five to eight mice per group.