Characterization of mature cells and B-cell development defect in KRNxG7 mice. (A) Systemic increase in myeloid cells and decrease in lymphoid cells. BM, spleen, liver, and PB cells were harvested from 6- to 8-week-old KRNxG7 and control (KRN, G7, or B6xG7) mice, stained for the indicated lineage markers, and analyzed by flow cytometry. B220 is a B-cell marker, Gr1 stains granulocytes and monocyte populations, Mac1 and F480 combination stains macrophages, and CD3, CD4, and CD8 stain T cells. Shown is the mean for 3 to 11 mice analyzed per strain for each tissue. (B) FACS plot for B-cell precursors in BM. BM cells from KRNxG7 or G7 controls are stained for B220 and AA4.1 (a marker for B-cell precursors). B-cell precursors (B220^loAA4.1⁺; arrow) are virtually depleted in KRNxG7 BM, whereas most of the residual cells are B220^hi and IgM⁺ (IgM staining not shown). (C) Systematic analysis of BM B-cell development. FACS determined frequency of various B-cell precursors from earliest (left) to the latest (right) are shown. Lymphoid primed multipotential progenitor (Kit⁺Sca1⁺Lin⁻Flk2^hiCD34⁺), CLP (Lin⁻Flk2⁺IL-7Rα⁺), PreproB (B220⁺IgM⁻CD19⁻CD43⁺NK1.1⁻CD11c⁻), ProB (B220⁺IgM⁻CD19⁺CD43⁺), PreB (B220⁺IgM⁻CD19⁺CD43⁻), and B cells (B220⁺IgM⁺). We confirmed that Lin⁻Flk2⁺IL-7Rα⁺ CLPs were almost predominantly Kit^loSca1^lo (data not shown) as previously reported.^19,20  (D) Expression of various B lymphopoiesis promoting cytokines in whole marrow. Expression was determined by quantitative real-time PCR, followed by normalization to GAPDH. IL-7, Flt3-L (ligand for Flk2), thymic stromal lymphopoietin (TSLP). *P < .05. **P < .01. ***P < .001.