WASp⁺ B cells exhibit a selective advantage beginning at the late transitional B-cell stage. Expression of WASp was determined in B-cell subsets derived from BM, spleen, and peritoneal cavity in female WASp heterozygous mice. Representative example of staining in (A) BM, (B) spleen, and (D) peritoneal cavity. Percentage of WASp-positive B cells in each subset in (C) spleen (n = 8) and (E) peritoneal cavity (n = 6).