Flow cytometric analysis of CXCR4 expression in B-cell progenitor maturation. (A) Representative flow histograms of CD34⁺/CD19⁺ B-cell progenitor (gate R2) and CD34^-/CXCR4⁺ later B cells (gate R3) sorted and analyzed for CCXCR4 and CCR7 expression. There was a surprisingly large fraction of CD34⁺/CD19⁺ B-cell progenitors that did not express the chemokine receptor CXCR4. More mature CD34^-/CD19⁺ BM B cells express CXCR4 at a high level. The percentage of each subpopulation relative to the total number of cells in gates R2 or R3 is shown. (B) Representative flow histograms of CD34⁺/CD19⁺/CXCR4^- cells cultured for 3 days in B-lymphoid conditions showing that the majority of cells lose expression of CD34 and a gain expression of CXCR4. The percentage of each subpopulation relative to the total number of cells is shown. (C) The majority of CD34⁺/CD19⁺/CXCR4^- cells cultured in B-lymphoid conditions gain expression of κ/λ light chains. Text data are the average of 3 distinct experiments; this figure shows a representative histogram.