NK cells in host responses to viral infections

• NK cells generate long-lived antigen-specific memory cells.
• NK cells regulate viral load and cytokine production of innate immune cells.
• NK cells indirectly modulate adaptive immune responses via innate immune cells.
• NK cells directly limit CD4+ T cell responses and their effects on CD8+ T cells.

Natural killer (NK) cells are cytotoxic innate lymphocytes that play an important role in viral clearance. NK cell responses to viral infections were originally believed to be non-specific and lacked immune memory recall responses. It is now appreciated that NK cell responses to viral infections can be specific and in some cases memory recall responses are established. Increasing evidence also illuminates the complexity of NK cell interactions with both innate and adaptive immune cells. Here, we summarize the evidence for NK cell-specific memory responses to viral infections and the intricate reciprocal interactions between NK cells and other immune cells that dictate their activation and effector functions.