IFN-gamma receptor signaling regulates memory CD8+ T cell differentiation.

IFN-gamma regulates multiple processes in the immune system. Although its antimicrobial effector functions are well described, less is known about the mechanisms by which IFN-gamma regulates CD8(+) T cell homeostasis. With the help of adoptive T cell transfers, we show in this study that IFN-gammaR signaling in CD8(+) T cells is dispensable for expansion, contraction, and memory differentiation in response to peptide vaccination. In contrast, host IFN-gammaR signaling counterregulates CD8(+) T cell responses and the generation of effector memory T cell processes, which are partially regulated by CD11b(+) cells. Similar to vaccination-induced proliferation, host IFN-gammaR signaling limits the expansion of naive CD8(+) T cells and their differentiation into effector memory-like T cells in lymphopenic mice. In contrast to peptide vaccination, IFN-gammaR signaling in CD8(+) T cells contributes to memory fate decision in response to lymphopenia, an effect that is fully reversed by high-affinity TCR ligands. In conclusion, we show that host IFN-gammaR signaling controls the magnitude of CD8(+) T cell responses and subsequent memory differentiation under lymphopenic and nonlymphopenic conditions. In contrast, IFN-gammaR signaling in CD8(+) T cells does not affect cell numbers under either condition, but it directs memory fate decision in response to weak TCR ligands.