Coordinated Viral Control by Cytotoxic Lymphocytes Ensures Optimal Adaptive NK Cell Responses

Natural killer (NK) cells play a critical role in controlling viral infections, coordinating the response of innate and adaptive immune systems. They also possess certain features of adaptive lymphocytes, such as undergoing clonal proliferation. However, it is not known whether this adaptive NK cell response can be modulated by other lymphocytes during viral exposure. Here, we show that the clonal expansion of NK cells during mouse cytomegalovirus infection is severely blunted in the absence of cytotoxic CD8(+) T cells. This correlates with higher viral burden and an increased pro-inflammatory milieu, which maintains NK cells in a hyper-activated state. Antiviral therapy rescues NK cell expansion in the absence of CD8(+) T cells, suggesting that high viral loads have detrimental effects on adaptive NK cell responses. Altogether, our data support a mechanism whereby cytotoxic innate and adaptive lymphocytes cooperate to ensure viral clearance and the establishment of robust clonal NK cell responses.