FACS analysis of thymocytes. Surface expression of (a) CD4 vs. CD8 on total thymocytes. The percentage of cells found in each quadrant is indicated. (b) TCRβ on total thymocytes. (c) CD44 and CD25 on DN thymocytes. Cells were triple stained with anti-CD44-FITC, anti-CD25-phycoerythrin, and a mixture of biotin-conjugated mAbs to CD3, CD4, CD8, B220, Mac1, and Gr-1, followed by streptavidin-CyChrome. Analysis was performed on gated CyChrome negative cells. Results are representative of three experiments.