Peripheral B-cell development and homeostasis in WASP^−/− mice. (A) Left panel; flow cytometric analysis of WT:WASP^−/− BM chimeric mice to define the percentage of WASP⁺ (CD45.2⁻) cells in the T1, FO, T2-MZP, and MZ B-cell populations, using CD21, CD23, and IgM as markers. The middle panel shows the results of one representative experiment, indicating (from top to bottom) the proportion of WASP⁺ (CD45.2⁻) cells in T2-MZP, FO, MZ B cells, and T1 cells, respectively. The right panel shows the percentage of WASP-expressing (CD45.1⁺) cells in the indicated B-cell populations. The hatched line indicates the 25% of WASP⁺ BM cells that were used for transplantation. The right panel represents data from one of 2 similar experiments with n = 7 mice. (B) Proportion of T1, T2-FO, FO, T2-MZP, and MZ B cells in WT and WASP^−/− mice (n = 10 mice per group). (C) Absolute numbers of T1, T2-FO, FO, T2-MZP, and MZ B cells in WT and WASP^−/− mice (n = 10 mice per group). (D) In vivo BrdU labeling. (Top panel) Mice were fed BrdU in the drinking water for 6 days (pulse) and followed for another 6 days (chase). Proportion of BrdU positive cells was assessed at day 3, 6, 9, and 14. (Bottom panels) The proportion of BrdU⁺ cells of T1, T2-FO, FO, T2-MZP, and MZ B cells as defined by CD21, CD23, CD24, and IgM expression is shown (n = 4 mice per group). *P < .05, **P < .01, ***P < .005.