Impaired development of splenic B cells in p85α^−/− mice is B-cell intrinsic. BM cells from the wild-type (p85α^+/+CD45.1⁺) and p85α-deficient (p85α^−/−CD45.2⁺) mice on a C57BL/6 background were transplanted into sublethally (3 Gy) irradiated PI3K-deficient (CD45.2⁺) and wild-type (CD45.1⁺) mice, respectively (bottom panels). Eight weeks after transplantation, splenocytes from recipient mice were stained with a combination of antibodies against B220, IgM, IgD, and CD45.2 (A) or B220, CD21, CD23, and CD45.2 (B), and analyzed on a FACSAria. Wild-type (WT) and p85α^−/− (KO) mice were also analyzed (top panels). Among B220⁺CD45.2⁺ cells (for p85α^−/− mouse–derived cells) or B220⁺CD45.2⁻ cells (for the wild-type mouse-derived cells), the percentages of the most mature IgM^loIgD^hi subset (A) and CD21^hiCD23^lo MZ B cells (B) are indicated. Data are representative of 3 mice in each type of transplantation.