RIAM-deficient mice are defective in T-cell-dependent humoral immunity. (A) IgA, IgM, IgG1, and IgG3 levels in serum of naive RIAM^+/+ (filled circles) and RIAM^−/− (open squares) mice. Data from individual animals are plotted along the Y-axis with horizontal lines indicating mean ± SD. The difference in IgM levels was statistically significant (P < .05). (B-C) Anti-TNP IgM and IgG3 levels in serum of RIAM^+/+ and RIAM^−/− mice measured by titration and ELISA, 7 (B-C) and 42 (C) days after intraperitoneal injection with the T-cell-independent immunogen TNP-Ficoll (B) or the T-cell-dependent immunogen TNP-KLH (C). A boost of TNP-KLH was given at day 35 (C). Titers shown are representative of 4 mice of each genotype immunized with each antigen. Anti-TNP IgM and IgG3 levels in mice immunized with TNP-KLH differed significantly at day 7 and 42 (* P < .05, ** P < .01, 2-way ANOVA).