Defective maintenance of peripheral B cells in the absence of Zfx. (A) The analysis of B-cell populations in the BM, spleen, and LNs of control and Mb1-Cre⁺Zfx^flox/y CKO mice at 4 to 6 weeks. Representative staining profiles are shown, with the percentages of select B-cell subsets indicated (mean ± SD of 5-7 mice per group). (Left) Splenic transitional type T1 (CD21^lowCD23^low) and T2 (CD21⁺CD23⁺), follicular (FO; CD21^int CD23^high), and marginal zone (MZ; CD21^highCD23^low); (middle) lymph node B cells; (Right) BM Fr. F recirculating B cells (IgM^intIgD^high). (B) The absolute number of B-cell subsets in control and Mb1-Cre⁺Zfx^flox/y CKO mice (mean ± SD of 5-7 mice per group). (C) The analysis of B-cell populations in the BM, LNs, and blood of control and CD19-Cre⁺Zfx^flox/y CKO mice at 8 to 12 weeks. The graphs show the absolute number of immature (Fr. E) and mature recirculating (Fr. F) BM B cells (mean ± SD of 10-11 mice), the absolute number of LN B220⁺ B cells (mean ± SD of 6 mice), and the fraction of blood B220⁺ B cells (mean ± SD of 3-5 mice). (D) B-cell turnover in control and CD19-Cre⁺Zfx^flox/y CKO mice. Mice were left untreated (open gray histograms) or fed BrdU for 2 weeks. Representative BrdU staining of splenic B220⁺ B cells and B220^hi IgD^hi recirculating BM B cells is shown. The graph indicates average percentage of BrdU⁺ B cells in individual control and CKO mice. Immature B cells in both control and CKO BM were 70% to 85% BrdU⁺ (not shown). (E) B-cell lifespan in control and CD19-Cre⁺Zfx^flox/y CKO mice pulsed with BrdU for 2 weeks. The graph shows the fraction of BrdU⁺ splenic B cells at the indicated time points after BrdU withdrawal (mean ± SD of 3 mice).