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Th1 and Th2 cell fates are traditionally viewed as mutually exclusive, but recent work suggests that these lineages may be more plastic than previously thought. When isolating splenic CD4(+) T cells from mice infected with the parasitic helminth Schistosoma mansoni, we observed a defined population of IFN-γ/IL-4 double-positive cells. These IFN-γ(+) IL-4(+) cells showed differences in DNA methylation at the Ifng and Il4 loci when compared with IFN-γ(+) IL-4(-) (Th1) and IFN-γ(-) IL-4(+) (Th2) cells, demonstrating that they represent a distinct effector cell population. IFN-γ(+) IL-4(+) cells also displayed a discrete DNA methylation pattern at a CpG island within the body of the Gata3 gene, which encodes the master regulator of Th2 identity. DNA methylation at this region correlated with decreased Gata3 levels, suggesting a possible role in controlling Gata3 expression. These data provide important insight into the molecular mechanisms behind the co-existence of Th1 and Th2 characteristics., (© 2014 The Authors. European Journal of Immunology published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)