CXCR4 expression in CD34⁺ thymic progenitor cells.

(A) Expression of CXCR4 on immature thymocyte subsets. CD34⁺ and CD4⁺ immature thymocytes purified as described in “Materials and methods” were stained with anti–CXCR4-PE. CXCR4 expression on DP cells was assayed by staining total thymocytes with anti–CD4-FITC, anti–CD8-PerCP, and anti–CXCR4-PE. Gray histograms show the expression of CXCR4 in each thymic cell subpopulation indicated in the figure. The percentages of positive cells and their mean fluorescence intensity (MFI) are indicated in each histogram. (B) Purified CD34⁺ cells were double stained with anti–CXCR4-FITC or -PE and a range of mAbs against differentiation-specific antigens. Solid histograms represent the expression of the indicated cell surface antigens on CD34⁺CXCR4⁻ and CD34⁺CXCR4⁺ thymocytes. The percentages of positive cells are showed in each histogram. Open histograms represent background fluorescence using isotype-matched irrelevant mAbs. Similar staining patterns were obtained in 4 different experiments.