Characterization of the Rosa26 ^LSL-EcoR allele. (A) Schematic diagram and expression of the Rosa26^LSL-EcoR allele. SLC7A1 (EcoR) protein expression was analyzed by flow cytometry in mature B cells from Cd23-Cre Rosa26^LSL-EcoR/+ and control Cd23-Cre Rosa26^+/+ mice and is displayed as a histogram or quantification of the geometric mean fluorescence intensity (gMFI). Statistical data are shown as mean values with SEM and were analyzed by the unpaired t test; ***P < 0.001. Each dot represents one mouse. (B) Flow cytometric analysis of B cells from Cd23-Cre Rosa26^LSL-EcoR/+ and control Cd23-Cre Rosa26^+/+ mice, which were transduced with ecotropic LV particles expressing the mCherry fluorescent reporter protein (mCherry-LV) and were subsequently cultured in vitro for 3 days in the presence of OP9 cells with sBAFF. The percentage of transduced mCherry⁺ B cells is shown. The bar graph indicates the transduction efficiency relative to all B cells. Statistical data are shown as mean values with SEM and were analyzed by the multiple unpaired t test with Holm–Šídák’s correction; ****P < 0.0001. Two experiments were performed, and each dot corresponds to one mouse. (C) Flow cytometric analysis of splenic B cells from Cd23-Cre Rosa26^LSL-EcoR/+ and control Cd23-Cre Rosa26^+/+ mice. The frequencies are shown for total B cells (CD19⁺B220⁺), immature B cells (CD19⁺CD93⁺), T1 B cells (CD19⁺CD93⁺IgM^hiCD23⁻), T2 B cells (CD19⁺CD93⁺IgM^hiCD23⁺), mature B cells (CD19⁺CD93⁻), MZ B cells (CD19⁺CD93⁻CD21^hiCd23^−/lo), FO B cells (CD19⁺CD93⁻CD21^loCD23^hi), GC B cells (CD19⁺B220⁺GL7⁺CD95⁺), and plasma cells (CD138⁺TACI⁺). (D) Flow cytometric analysis of bone marrow plasma cells from Cd23-Cre Rosa26^LSL-EcoR/+ and control Cd23-Cre Rosa26^+/+ mice. (E) Quantification of the number of total B, immature B, mature B, GC B, and plasma cells in the spleen, and plasma cells in the bone marrow from Cd23-Cre Rosa26^LSL-EcoR/+ and control (Cd23-Cre Rosa26^+/+ and Rosa26^+/+) mice. Statistical data are shown as mean values with SEM. All pairwise comparisons are nonsignificant, as analyzed by the multiple unpaired t test with Holm–Šídák’s correction test. Two (A and B) and three (C–E) independent experiments were performed. Each dot represents one mouse.