B cell–specific deletion of Cdc42 has no effect on early B-cell development in bone marrow but impairs late B-cell development in spleen. (A) Bone marrow cells from WT and Cdc42^−/− (KO) mice were counted and stained with antibody against B220 and IgM. Immunopositive cells were analyzed by flow cytometry. The number of B-cell subsets was calculated by multiplying the total number of bone marrow cells by the percentage of cells of each subset. (B) ProB/preB and immature B cells from bone marrow were collected by fluorescence-activated cell sorting (FACS) and subjected to PCR analysis of Cdc42 WT, floxed, and KO alleles. (C) Splenocytes were isolated, counted, and stained with antibodies against B220, IgM, IgD, CD21, and CD23. Immunopositive cells were analyzed by flow cytometry. The number of cells within each of the B-cell subsets was calculated as described in panel A. (D) Cells from peritoneal lavage fluid (PLF) were counted and stained with antibodies against IgM and CD5. Immunopositive cells were analyzed by flow cytometry. The number of B-1a cells was calculated by multiplying the total number of PLF cells times the percentage of B-1a cells (**P < .01; *P < .05). Data are means ± SD.