Interferon-gamma acts directly on CD8+ T cells to increase their abundance during virus infection.

Interferon-gamma (IFNgamma) is important in regulating the adaptive immune response, and most current evidence suggests that it exerts a negative (proapoptotic) effect on CD8(+) T cell responses. We have developed a novel technique of dual adoptive transfer, which allowed us to precisely compare, in normal mice, the in vivo antiviral responses of two T cell populations that differ only in their expression of the IFNgamma receptor. We use this technique to show that, contrary to expectations, IFNgamma strongly stimulates the development of CD8(+) T cell responses during an acute viral infection. The stimulatory effect is abrogated in T cells lacking the IFNgamma receptor, indicating that the cytokine acts directly upon CD8(+) T cells to increase their abundance during acute viral infection.