Provision of WT T_reg cells prevents IBD development in Bcl11b^F/F/CD4-Cre mice. (A) Sorted WT Foxp3-GFP⁺ T_reg cells were transferred into 4–5-wk-old Bcl11b^F/F/CD4-Cre mice, as described in Materials and methods, and the weight of the mice was assessed weekly. Asterisks indicate statistical significance between the T_reg cell transferred and untransferred groups (*, P < 0.05; determined by unpaired two-tailed Student’s t test). (B) Colon gross anatomy of Bcl11b^F/F/CD4-Cre (KO), WT T_reg cell–transferred Bcl11b^F/F/CD4-Cre (WT Tregs → KO), and WT mice. (C) H&E staining of colon sections from the mice in B. (D) Alcian blue counterstained with Nuclear Fast red of colon sections from the mice in B. Goblet cells are blue. (C and D) Histological images are from similar areas along the length of the colon of the three groups of mice. Bars, 100 µm. (E) Histological scores of colitis, conducted as described in Table S1. (P < 0.05, determined by unpaired two-tailed Student’s t test.) Error bars indicate SD. (F) CD4⁺ and CD8⁺ T cell frequencies within the total lymphocyte population isolated from colon LP and epithelial compartment (IEL). (A–F) Data are representative of two independent experiments with three to five mice per group. (G) Intracellular cytokines in gated CD4⁺ T cells isolated from the colon of the indicated groups of mice. (H) Sorted WT CD45.1⁺/CD45.2⁺/Foxp3-GFP⁺ T_reg cells were transferred into Bcl11b^F/F/CD4-Cre/CD45.2⁺ mice, and WT (CD45.1⁺) and Bcl11b-deficient (CD45.1⁻) cells were evaluated 6–7 wk after the transfer. Splenocytes were stained for CD4, CD45.1, and Foxp3 and analyzed by flow cytometry. Numbers in boxes indicate the frequencies of the donor (CD45.1⁺) and recipient (CD45.1⁻) cells within the Foxp3⁺ population. Foxp3 mean fluorescence intensity (MFI) in Bcl11b-deficient and WT cells is indicated. (G and H) Data are representative of three independent experiments each with two to three mice per group.