FACS analysis of cells recovered from cultured fetal thymi from Rag1- or IL-7–deficient mice under various conditions. (A) CD25/CD44 staining of CD4^–CD8^– cells or CD4/CD8 staining of total thymocytes from Rag-deficient FTOCs. The number at the bottom-right corner indicates the percentage of CD25⁺CD44^– DN3 cells, and that at the top left indicates the percentage of CD4^–CD8⁺ cells. (B) CD25/CD44 staining of CD4^–CD8^– cells from IL-7–deficient FTOCs. The number at the top-right corner indicates the percentage of CD25⁺CD44⁺ DN2 cells.