B-cell subpopulations are altered in the BM and spleen. (A) Cells isolated from BM of WT and KI mice (N = 5 each) were stained with antibodies to IgM and B220. Populations are labeled as follows: M indicates mature B cells; IMM, immature B cells; and Pro-pre, Pro/Pre B cells. There were fewer Pro/Pre and immature B cells in KI mice. (B) Cells isolated from the BM of WT and KI mice were stained with antibodies to B220, CD24, and CD43. Stages of B-cell development are based on the following: B220⁺CD24⁺CD43⁻: small pre-B, immature B, and mature B cells; B220⁺CD24⁺CD43⁺: late pro-B and large pre-B cells; B220⁺CD24⁻CD43⁺: early pro-B cells. Populations of CD43⁺ and CD24⁺ cells from the BM of WT and KI mice. There were more CD43⁺, CD24⁺ cells in the KI compared with WT mice. (C) Flow cytometric analyses revealed that mature B-cell populations were increased in KI spleens. (D) B220⁺ cells were also stained with IgM and IgD antibodies, and stages of B cells were identified by the following cell surface markers: M indicates mature B cells (B220⁺ IgD^highCD21⁺IgM⁻); T, transitional B cells (T1, B220⁺IgD^loCD21^loIgM^high; T2, B220⁺IgD^highCD21^highIgM^high); and MZ, marginal zone B cells (B220⁺IgD⁻CD21^highIgM^high). Sample sizes for these experiments were 5 mice/group (ages, 8 to 9 weeks) and are representative of repeat experiments.