BATF KO iT_reg cells, although equally suppressive in vitro as WT iT_reg cells, are unable to suppress colitis. BATF KO and WT iT_reg cells were prepared in vitro from naive CD4⁺ T cells through activation with concanavalin A in the presence of TGFβ1 and 10 nM RA for 6 d. (A) The iT_reg cells were examined for their suppressive activity on proliferation of target (CD4⁺CD25⁻) T cells based on frequencies (percentages) of CFSE-diluted cells determined by flow cytometry. (B–E) Rag1^−/− mice were injected i.p. with 0.6 × 10⁶ WT CD45.1⁺ naive CD4⁺CD25⁻ T cells and 1.2 × 10⁶ WT or BATF KO CD45.2⁺ iT_reg cells, and weight change (B), histological changes on day 25–28 (C), frequencies of Th1, Th17, and FoxP3⁺ T cells derived from the naive CD4⁺CD25⁻ T cells (D), and frequencies of FoxP3⁺ cells derived from the injected iT_reg cells (E) were examined. Bars, 200 µm. The mice (n = 9–10/group) were sacrificed on day 25–28 after T cell transfer when some mice lost >20% of their original weight. Pooled data obtained from three experiments are shown in the graphs. All error bars are SEM obtained from pooled data. Significant differences between indicated groups or between WT and BATF KO groups are shown (*, P < 0.05).