Thymic development in IL-7^–/– mice. (A) Total number of thymocytes in B6 (•) and IL-7^–/– (○) mice at the indicated ages after birth. Mean (± SD) from groups of 3 to 6 mice per time point is shown, except at 16 weeks where individual mice are depicted. (B) Flow cytometric analysis of thymocytes from B6 (left panels) and IL-7^–/– (right panels) mice stained with CD8 and CD4 (top panels) at 8 weeks of age. Bottom panels show the coexpression of CD25 and FOXP3 in gated CD4⁺ SP subset. The mean (± SD) of groups of 3 to 6 mice is shown in the indicated quadrants.