Positive selection of human fetal CD25^hi thymocytes. (A) CD3, CD1a, CD69, and CD25 expression in CD4^-CD8^- (DN), CD4⁺CD8⁺ (DP), CD4⁺CD8^lo (CD4int), and CD4⁺CD8^- (CD4SP) thymocytes gated as shown on the bottom left panel. Numbers indicate cell percentages in each quadrant. Data from 20-WG fetuses are shown. (B) Mean percentages ± SD of CD1a⁺ and CD69⁺ cells in CD25⁺ and CD25^- lymphocytes within subsets defined as in panel A. Cells were obtained from 8 fetuses (13 to 29 WGs) for CD69 analyses and 6 fetuses (14 to 24 WGs) for CD1a analyses. ^*P < .05 by Student t test.