Normal apoptosis and proliferation of B cells in Rap1b-deficient mice. (A) Normal apoptosis in naive Rap1b-deficient MZ B cells. Splenocytes from wild-type (+/+) and Rap1b-deficient (−/−) mice were stained with anti-IgM, anti-CD21, and anti-CD23 antibodies. The degree of TUNEL positivity in the gated MZ B cells (CD23−CD21hiIgMhi) was determined by FACS analysis. Percentages indicate TUNEL-positive cells in the gated B-cell subpopulations. Data are representative of 3 independent analyses. (B) Statistical analysis of the percentages of TUNEL-positive MZ B cells from panel A (3 mice of each genotype). (C) Normal proliferation of Rap1b-deficient MZ B cells in vivo. Wild-type and Rap1b-deficient mice were injected with BrdU every 12 hours for 4 days. Splenocytes from the mice were stained with anti-IgM, anti-CD21 and anti-CD23 antibodies. Cells were then permeabilized, fixed, and stained with FITC-conjugated anti-BrdU. The degree of BrdU positivity in the gated MZ B cells (CD23−CD21hiIgMhi) was determined by FACS analysis. Percentages indicate BrdU-positive cells in the gated B-cell subpopulations. Data are representative of 2 mice per genotype. (D) Statistical analysis of the percentages of BrdU-positive MZ B cells from panel C (2 mice of each genotype). (E) Normal proliferation of Rap1b-deficient MZ and FO B cells in response to LPS in vitro. MZ (CD23−CD21hiIgMhi) and FO (CD23+CD21intIgMlo) B cells were sorted from the splenocytes of wild-type or Rap1b-deficient mice and then stimulated with LPS for 48 hours. Proliferative responses were determined by [3H]thymidine incorporation. Data are representative of 3 independent experiments. (F) Normal proliferation of Rap1b-deficient splenic mature B cells in response to LPS, anti-IgM, or anti-IgM plus IL-4 in vitro. Splenic mature B cells were purified from the splenocytes of wild-type or Rap1b-deficient mice and then stimulated with LPS, anti-IgM or anti-IgM plus IL-4 for 48 hours. Proliferative responses were determined by [3H]thymidine incorporation. Data are representative of 2 independent experiments.