Normal B1 B cells, reduced lymph node B cells, and an intrinsic MZ B-cell defect in Rap1b-deficient mice. (A) B1 B cells in the peritoneal cavities of wild-type and Rap1b-deficient mice. Peritoneal cells from wild-type (+/+) and Rap1b-deficient (−/−) mice were stained with anti-B220 and anti-CD5 antibodies. Percentages indicate cells in the gated lymphoid populations. Data are representative of 6 mice per genotype. (B) The percentages of B1a, B1b, and B2 B cells in the peritoneal cells of wild-type and Rap1b-deficient mice. Data shown were obtained from 6 mice of each genotype. (C) The numbers of B and T cells in the lymph nodes of wild-type and Rap1b-deficient mice. Lymphocytes from inguinal (ILN), axillary (ALN), and mesenteric (MLN) lymph nodes of wild-type and Rap1b-deficient mice were stained with anti-B220 and anti-thy1.2 antibodies, and the numbers of B and T cells in ILN, ALN and MLN were determined. Data shown were obtained from 14 mice of each genotype for ILN and ALN and 12 mice of each genotype for MLN. (D) MZ B-cell defect in Rap1b-deficient mice is B-cell intrinsic. Sublethally irradiated JAK3-deficient mice were transplanted with BM from wild-type (Rap1b^+/+ + JAK3^−/−) and Rap1b-deficient (Rap1b^−/− + JAK3^−/−) mice. Sublethally irradiated JAK3-deficient mice without BM transplantation (JAK3^−/−) were used as a negative control. Eight weeks after transplantation, splenocytes from recipient mice were stained with anti-B220, anti-CD21, and anti-CD23 antibodies. In B220⁺-gated cells, MZ B cells (CD21^hiCD23^lo) are shown. Percentages indicate cells in the gated B220⁺ lymphoid populations. Data are representative of 4 recipients transplanted with Rap1b^+/+ BM, and 5 recipients transplanted with Rap1b^−/− BM. The mean (± SD) for the data from all of the recipients in each type of transplantation has been summarized in a bar graph (right).