Defects in splenic and BM B-cell development in KA/KA mice. (A) Analysis of the total splenic B-cell population of WT and KA/KA mice at 6 weeks of age using flow cytometry with the indicated B-cell surface markers B220⁺CD90.1⁺, B220⁺CD19⁺, B220⁺IgM⁺, B220⁺IgD⁺, CD21⁺CD23⁻ (B220⁺ gate), and CD21^loCD23^hi (B220⁺ gate). Numbers are the percentage of the cell population; MZ, marginal zone; FO, follicular. (B) Analysis of BM cells isolated from WT and KA/KA mice at 6 weeks of age using flow cytometry with B-cell and progenitor-cell markers. A combination of markers was used to define pre-pro-B cells (B220⁺CD43^hiCD19⁻BP1⁻CD24^loIgM⁻), pro-B cells (B220⁺CD43^medBP-1⁺CD19⁺ IgM⁻), and pre-B cells (B220^hiCD43⁻CD19⁺IgM⁻).