Asymmetric induction of Th1 versus Th2 apoptosis by Tregs. The effect of Tregs on the proliferation and apoptosis of Th1 and Th2 cells was determined by measurement of BrdU incorporation, Ki67 expression, and activated caspase 3 expression within IL-4– and IFNγ-producing cells in the lymph nodes of wild-type and DT-treated Foxp3^DTR mice. (A) Wild-type and DT-treated Foxp3^DTR mice were treated daily with BrdU from the time of DT administration, and incorporation was measured in IFNγ-expressing Th1 cells and IL-4–expressing Th2 cells (n = 5/group). (B) Ki67 expression in Th1 and Th2 subsets of wild-type and DT-treated Foxp3^DTR mice (n = 9, 11). (C) Activated caspase 3 expression in Th1 and Th2 subsets of wild-type and DT-treated Foxp3^DTR mice (n = 9, 11). (D) The effect of Tregs on Th1 and Th2 subsets, measured by calculating the percentage change in Ki67 and activated caspase 3 expression in wild-type versus DT-treated Foxp3^DTR mice. Each diamond represents an individual wild-type mouse (n = 9), normalized to the average value of DT-treated Foxp3^DTR mice (n = 11). Error bars indicate SD.