This study follows on from previous work by the same group using nuclear factor of activated T cells (NFAT)-1 knockout mice. Their previous observation was that T cells from NFAT-1 knockout mice have a strong bias to differentiate into Th2 cells, thus producing increased levels of IL-4 relative to T cells from NFAT+/+ littermates. They have noted also that naive NFAT-/- T cells produced less IFN-? than naive NFAT+/+ T cells. However, because the latter could be due to overexpression of IL-4 they created a double-deficient NFAT-/- IL4-/- line. In this study, they show that, in the absence of endogenous production of IL-4, CD4+ T cells lacking NFAT display a cell-intrinsic defect in IFN-? production.