Age-dependent changes IL-7Rα Tg thymus. (A) Thymic cellularity was enumerated at the indicated ages; the bars represent the SEM for each point. Data from B1 and C10 mice, which have similar Tg IL-7R levels and behaved similarly, were pooled. Two to 12 mice are shown per experimental time point. (B) Thymocyte CD4/CD8 profiles are shown for representative mice at 8 weeks of age. (C) The absolute number of DN thymocytes from 3 wild-type and 4 B1 or C10 mice of 8 to 10 weeks of age is shown. (D) DN thymocytes from the indicated strains were examined for expression of CD44 and CD25. (E) The averaged absolute numbers of wild-type (▪) or B1 and C10 (□) cells present in the different DN subpopulation from 3 independent experiments are shown. (F) Surface expression of IL-7Rα is shown on the indicated DN subpopulation, as gated in panel D: DN2 (CD44⁺CD25⁺), DN3 (CD44^-CD25⁺), and DN4 (CD44^-CD25). The curves represent cells from wild-type (thin line), D4 (dashed line), and C10 (thick line) thymi. Because of the different numbers of cells recovered between the strains, the results are normalized to the number of cells in the largest peak. Control staining is shown only in the first histogram. The bars represent the SEM.