Foxp1-deficient T cells acquire the activated phenotype during the differentiation from DP stage to SP stage. (A) Diagram of intrathymic adoptive transfer. (B) CD44 expression of donor thymocytes 3 days after the intrathymic transfer by staining. Data are representative of various time points (days 3, 5, and 6) in at least 2 independent experiments. The histogram with solid gray represents Foxp1^f/+Cd4^Cre mice, the histogram with dark line represents Foxp1^f/fCd4^Cre mice. (C) Foxp1-deficient CD8 SP thymocytes readily produce IFN-γ ex vivo. FACS-sorted CD8 SP thymocytes from 6-week-old Foxp1^f/+Cd4^Cre and Foxp1^f/fCd4^Cre mice were stimulated with PMA and ionomycin for 4 hours and analyzed for IFN-γ production by intracellular staining. Data are representative of 2 independent experiments.