Th2 Cells Cannot Induce FOXP3 Expression
(A) Human T cells were activated with plate-bound anti-CD3/CD28 with or without TGF-β as indicated on the x-axis of (B). Cells were harvested after 5 days and FOXP3 mRNA was quantified by real-time PCR. Bars show the mean ± SD of 4 independent experiments.
(B) In vitro differentiated Th1, Th2, or iTreg cells were activated with anti-CD3/CD28, TGF-β, or anti-IL-4 as indicated. The phenotype of these cells was confirmed by FACS and proliferation analysis (Figure S1). Bars show the mean ± SD of four independent experiments.   Th2 cells are known to produce IL-4 upon activation, which may interact with TGF-β signaling and thus prevent FOXP3 induction.