Fig 3. Foxp1 regulates rTreg cell quiescence in a cell-intrinsic manner.

(A) Flow cytometry analysis of Ki-67 expression in Foxp3⁺YFP⁺ rTreg and aTreg cells in the spleens from Foxp3^Cre/+ and Foxp1^f/fFoxp3^Cre/+ female mice; numbers above bracketed lines indicate the percentages of Ki-67⁺ Treg cells. (B) Flow cytometry analysis of Foxp3⁺YFP⁺ Treg cells from spleens and lymph nodes of Foxp3^Cre/+ and Foxp1^f/fFoxp3^Cre/+ female mice (left panel), and frequencies of Foxp3⁺YFP⁺ Treg cells (right panel) (n = 5). (C) Frequencies of Foxp3⁺YFP⁺ aTreg cells in CD4⁺ T cells, n = 5. (D-F) Foxp1^f/f and Foxp1^f/fCre-ERT2⁺ mice were treated with tamoxifen, and phenotypes were analyzed at d8 after treatment. (D) Flow cytometry analysis of CD44 and CD62L expression in CD4⁺Foxp3⁻ conventional T cells from Foxp1^f/f and Foxp1^f/fCre-ERT2⁺ mice; numbers adjacent to the outlined areas indicate the percentages of naive cells (CD44^lowCD62L^high) or activated cells (CD44^highCD62L^low). (E) Flow cytometry analysis of CD44 and CD62L expression in Treg cells from Foxp1^f/f and Foxp1^f/fCre-ERT2⁺ mice; numbers adjacent to the outlined areas indicate the percentages of rTreg cells (CD44^lowCD62L^high) or aTreg cells (CD44^highCD62L^low). (F) Flow cytometry analysis of Ki-67 expression in rTreg and aTreg cells from Foxp1^f/f and Foxp1^f/fCre-ERT2⁺ mice. Numbers above bracketed lines indicate percentages of Ki-67⁺ Treg cells. Data in (A-F) are representative of at least two independent experiments. Data in (B: right panel, C) are mean ± SEM, *P < 0.05 (two-tailed Student t test). Data associated with this figure can be found in the supplemental data file (S1 Data). aTreg, activated Treg; CD, cluster of differentiation; d, day; Foxp1, forkhead box P1; Ki-67, antigen identified by monoclonal antibody Ki 67; ns, no significance; rTreg, resting Treg; Treg, regulatory T; YFP, yellow fluorescent protein.