Impaired humoral responses in BMKO mice. (A) Serum from control and BMKO mice (n = 7–10) was analyzed by ELISA to determine levels of the indicated Igs. Horizontal bars are the geometric mean. (B) Littermate control and BMKO mice (n = 6) were i.p. immunized with TNP-Ficoll and serum was analyzed as for A on the indicated days after immunization to detect anti-TNP IgM (left) and anti-TNP IgG3 (right). Results are expressed as a serum dilution factor. Horizontal bars are the geometric mean. (C) Littermate control and BMKO mice (n = 6) were i.p. immunized with NP₍₁₅₎-CGG. Left, serum was analyzed as in B to detect NP-specific IgG1. Right, representative flow cytometric analysis of GC B cells (PNA^hiCD38^lo) among gated B220⁺ cells from control and BMKO mice before immunization (No-imm) and at 14 d after immunization (NP-CGG). Numbers indicate the percentage of GC B cells. Data shown are from a single experiment involving four to five mice per genotype. Horizontal bars are the geometric mean. (D) Littermate control and BMKO mice (n = 5–6) were i.v. injected with 10⁵ pfu VSV. Serum was analyzed on day 0 (before infection) and on days 2, 4, 6, 10, and 12 after VSV infection to detect the total anti-VSV IgM plus IgG titer (left) or the VSV-specific IgG titer (right). Results are the combined mean ± SD (n = 5–6; *, P < 0.05; **, P < 0.005). Ab titration data are from a single experiment involving 6–10 mice per genotype (A and B), or from two independent experiments involving two to three mice per genotype analyzed together (D).