Foxp1-deficient Treg cells develop normally and are functional. (A) Staining of cell-surface CD4 and CD25 and intracellular Foxp3 in the thymuses, lymph nodes, and spleens of 10-week-old Foxp1^f/+Cd4^Cre and Foxp1^f/fCd4^Cre mice. The percentages of CD25⁺Foxp3⁺ cells in CD4⁺ T cells were shown. Data are representative of 2 independent experiments. (B) Total cell numbers of Treg cells in the thymuses, lymph nodes, and spleens of Foxp1^f/+Cd4^Cre and Foxp1^f/fCd4^Cre mice at different ages. Bars represent average ± SD, weeks 4-5: n = 5, weeks 8-10: n = 7, and weeks 21-22: n = 5. (C) In Treg cell suppression cocultures, CFSE-labeled control CD4⁺ T cells were incubated with various ratios of Treg cells from Foxp1^f/+Cd4^Cre or Foxp1^f/fCd4^Cre mice. The IFN-γ production by control CD4⁺ T cells was analyzed by intracellular staining. Data are representative of 2 independent experiments.