Reduction of thymic Foxp3⁺ CD4⁺ T cells with tissue-specific diminution of Stat5a/b levels. (A) CD25 and Foxp3 expression were assessed on sorted CD4 SP thymocytes from Stat5^fl/fl mice and YFP⁺CD4 SP thymocytes from Stat5^fl/−, CD4Cre, Yfp mice. (B) Average proportion of CD4 SP thymocytes. (C) Mean percentage of Foxp3⁺ CD4⁺ T cells. (D) Average total numbers of thymocytes. (E) Absolute numbers of Foxp3⁺ CD4⁺ T cells. Means ± SE (n = 6) are shown; *P < .01 as determined by Student t test. Numbers indicate the percentage of CD25⁺ or FoxP3⁺ cells delineated by the rectangles.