Normal B-cell development in young IgH.T and IgH.TEμ mice. (A) Proportions of pro-B (CD19⁺/CD43⁺/μ⁻), pre-B (CD19⁺/μ⁺), immature (IgM⁺/IgD⁻), and mature (IgM⁺/IgD⁺) B cells in BM and total CD19⁺ B cells in the spleen of the indicated mice, as measured by flow cytrometric analysis. Mean values and SD are given for 4 mice per group. (B) Fluorescence-activated cell sorter profiles for IgM and IgD in total spleen cells from the indicated mouse groups (top panel). Total splenic CD19⁺ B cells were gated and analyzed for CD21 and CD23 expression. The proportions of CD21^highCD23^high follicular B cells and CD21^hiCD23^lo marginal zone B cells within the specified gates are given. (C) Flow cytrometric analysis of CD19 expression (top panel) on peripheral white blood cells of WT, IgH.T, and IgH.TEμ mice at 2 months of age. The CD19⁺ fraction was gated and analyzed for the expression of the IgM^a and IgM^b allele (bottom panel). Numbers in the plots indicate the percentage of cells within the specified gates. (D) Quantitative PCR analysis of large T mRNA expression in CD19⁺ BM cells and spleen cells of the indicated mice. Expression was normalized with HPRT, and expression in IgH.TEμ BM was set to 1. Significant differences compared with IgH.TEμ mice (* P < .01, ** P < .001, Mann-Whitney U test). Mean values and SD are given for 3 mice (8-10 weeks old) per group.