Bcl11b^F/F/Foxp3-Cre mice fail to gain weight only after 20 wk of age and show colon inflammation with infiltration of proinflammatory cytokine–producing CD4⁺ T cells. (A) Weight of Bcl11b^F/F/Foxp3-Cre mice between 2 and 6 mo of age. 6–10 mice/group were evaluated. Asterisks indicate statistical significance determined by unpaired two-tailed Student’s t test (*, P < 0.05). (B) Colon gross anatomy representative for 5–6-mo-old Bcl11b^F/F/Foxp3-Cre mice and age-matched controls. (C) H&E staining (top) and Alcian blue counterstained with Nuclear Fast red (bottom) of colon sections of 5–6-mo-old Bcl11b^F/F/Foxp3-Cre and age-matched controls. Goblet cells are blue. Histological images are from similar areas along the length of the colon. Bars, 100 µm. (B and C) Data are representative of five pairs of mice. (D) Colitis histological scale of 5–6-mo-old Bcl11b^F/F/Foxp3-Cre and age-matched controls, using the criteria in Table S1. (A and D) Error bars indicate SD. (E) Frequencies of CD4⁺ and CD8⁺ T cells in spleen of Bcl11b^F/F/Foxp3-Cre and WT mice. (F) Frequencies of CD44⁺CD4⁺ T cells in spleen of Bcl11b^F/F/Foxp3-Cre and WT mice. Data are representative of three pairs of mice. (G) Frequencies of CD4⁺ and CD8⁺ T cells in the colon LP and intraepithelial compartment (IEL) of Bcl11b^F/F/Foxp3-Cre and WT mice. (H) Cytokine production by CD4⁺ T cells isolated from Bcl11b^F/F/Foxp3-Cre and WT mice colons. Cells were isolated and activated as described in Materials and methods, followed by staining for surface CD4 and intracellularly for the indicated cytokines, and analyzed by flow cytometry. Frequencies of cytokine-producing CD4⁺ T cells are indicated. Data are representative of three pairs of mice.