Peripheral Foxp1-deficient T cells have reduced cell numbers and an activated phenotype. (A) Total cell numbers of CD4⁺ T and CD8⁺ T cells in the lymph nodes and spleens of Foxp1^f/+Cd4^Cre and Foxp1^f/fCd4^Cre mice at different ages. Data represent average ± SD, weeks 4 to 5: n = 5, weeks 8-10: n = 7, and weeks 21-22: n = 5. *P < .05; **P < .01; ***P < .001. (B) Expression of CD44 or CD62L in splenic CD4⁺ T or CD8⁺ T cells from Foxp1^f/+Cd4^Cre and Foxp1^f/fCd4^Cre mice at different ages. Data are representative of at least 3 independent experiments. The histogram with solid gray represents Foxp1^f/+Cd4^Cre mice, and the histogram with dark line represents Foxp1^f/fCd4^Cre mice.