Interleukin-10 production by regulatory CD4+Â T cells during resolution of infection promotes memory CD8+Â T cell maturation

Memory CD8+ T cells are critical for host defense upon reexposure to intracellular pathogens. We found that IL-10 derived from regulatory CD4+ T cells (Tregs) is necessary for memory CD8+ T cell maturation following acute LCMV infection. Treg-derived IL-10 was most important during the resolution phase of infection, calming inflammation and the activation state of dendritic cells. Adoptive transfer of IL-10-sufficient Tregs during the resolution phase of viral infection rescued CD8+ T cell memory maturation in IL-10-deficient mice. These data indicate that Treg-derived IL-10 is necessary to insulate CD8+ T cells from inflammatory signals, and reveal that the resolution phase of infection is a critical period that influences the quality and function of developing memory CD8+ T cells.