Cutting edge:: Early IFN-γ signaling directly enhances primary antivliwal CD4+ T cell responses

IFN-gamma drives CD4(+) T cell differentiation toward the Th1 phenotype (T(h)1) and suppresses T(h)2 development. Current. evidence indicates that IFN-gamma inhibits T cell proliferation and decreases T cell survival In contrast to the above, we show here that antiviral CD4+ T cell generation after infection is reduced in the absence of IFN-gamma signals. The deficient expansion of cells was not due to perturbations in T cell sensitivity to peptide or to altered migratory patterns through nonlymphoid tissues. Instead, IFN-gamma enhanced early antiviral CD4 responses largely through direct signals into these cells. Our data challenge prevailing dogma and have implications for how the sizes of the CD8(+) and CD4(+) T cell responses are established.