Environmental signals influencing expression of the IFN-gamma receptor on human T cells control whether IFN-gamma promotes proliferation or apoptosis.

IFN-gamma R expression is subject to contrasting modulation on human T cells. IFN-gamma R constitutive expression is low on three human malignant T cells (ST4, PF382, and Jurkat) growing in medium supplemented with serum. The addition of IFN-gamma down-modulates IFN-gamma R expression and increases both proliferation and MHC class I Ag expression. By contrast, when malignant T cells are cultured in medium without serum, IFN-gamma R expression dramatically increases and the cells undergo a slow apoptotic death. The addition of IFN-gamma enhances apoptosis and inhibits cell rescue in serum-supplemented medium. This opposite ability of IFN-gamma to stimulate malignant T cell proliferation or death correlates with the intensity of IFN-gamma R cell expression, high expression being a marker for cell apoptosis. IFN-gamma R up-modulation also occurs on malignant T cells undergoing apoptosis after treatment with dexamethasone, on irradiated normal CD3+ PBL, and on cultured normal CD3+ thymocytes. Moreover, the ability of IFN-gamma to augment apoptosis of highly IFN-gamma R-positive thymocytes suggests that its role in promoting T cell apoptosis is also important in physiologic conditions.