Progressive lymphocytopenia in XLF-deficient mice. (A) Representative flow cytometric analysis of B cells in the spleen of XLF^−/− mice and XLF^+/+ littermates. Absolute number of mature B220⁺IgM⁺ B cells (B) and CD4⁺CD8⁻ T cells (C) in the spleen of XLF^−/− mice and XLF^+/+ littermates; P < 2 × 10⁻⁷. (D) Representative flow cytometric analysis of B cells in the BM in XLF^−/− mice and XLF^+/+ littermates. (E) Percentage of total B220⁺ B cells in the BM of XLF^−/− mice and XLF^+/+ littermates; P = 1.4 × 10⁻⁷. n ≥ 3 per age group per genotype. Data represent mean ± standard deviation in all graphs. The P values in this figure were calculated by comparing the slope of regression lines between XLF^+/+ and XLF^−/− mice with Student t test. IgM, immunoglobulin M.