Interferon gamma stabilizes the T helper cell type 1 phenotype

T helper cell (Th)1-primed CD4 T cells from wild-type donors make little in terleukin (IL)-4 when restimulated under Th2 conditions. However, such rest imulation of Th1-primed cells from interferon (IFN)-gamma (-/-) or IFN-gamm a receptor (IFN-gammaR)(-/-) mice resulted in substantial production of IL- 4 and other Th2 cytokines. Adding IFN-gamma to the priming culture markedly diminished the capacity of Th1-primed IFN-gamma (-/-) cells to express IL- 4. Even IFN-gamma -producing cells from IFN-gammaR(-/-) mice could acquire IL-4-producing capacity. Thus, IFN-gamma is not required for the developmen t of IFN-gamma -producing capacity, but it plays a critical role in suppres sing the IL-4-producing potential of Th1 cells.