Marked reduction of MZ B cells in Rap1b-deficient mice. (A) The numbers of total splenocytes and total splenic B and T cells in wild-type and Rap1b-deficient mice. Data shown are obtained from 10 mice of each genotype. (B) B and T cells in the spleens of wild-type and Rap1b-deficient mice. Splenocytes from wild-type (+/+) and Rap1b-deficient (−/−) mice were stained with anti-B220 and anti-Thy1.2 antibodies. Percentages indicate cells in the gated lymphoid population. Data are representative of 10 mice per genotype. (C) T1, T2, FO, and MZ B cells in the spleens of wild-type and Rap1b-deficient mice. Splenocytes from wild-type and Rap1b-deficient mice were stained with anti-IgM, anti-CD21 and anti-CD23 antibodies. In cells gated on CD23⁺, T2 (CD23⁺CD21^hiIgM^hi) and FO (CD23⁺CD21^intIgM^lo) B cells are shown. In cells gated on CD23⁻, T1 (CD23⁻CD21^loIgM^hi) and MZ (CD23⁻CD21^hiIgM^hi) B cells are shown. Percentages indicate cells in the gated lymphoid populations. Data are representative of 10 mice per genotype. (D) MZ B cells in the spleen of wild-type and Rap1b-deficient mice. Splenocytes from wild-type and Rap1b-deficient mice were stained with anti-B220, anti-CD21, and anti-CD23 antibodies. In cells gated on B220⁺, MZ B cells (CD21^hiCD23^lo) are shown. Percentages indicate cells in the gated B220⁺ lymphoid populations. Data are representative of 10 mice per genotype. (E) The numbers of T1, T2, FO, and MZ B cells in the spleen of wild-type and Rap1b-deficient mice. Data shown are obtained from 10 mice of each genotype. (F) Immunofluorescence histochemical analysis of MZ B cells in the spleen of wild-type and Rap1b-deficient mice. Frozen splenic sections derived from wild-type and Rap1b-deficient mice were stained with anti-MOMA-1 (green) and anti-IgM (red). MZ B-cell layer external to the ring of metallophilic macrophages is indicated by arrows. The data shown are representative of 2 independent experiments.