Metabolic Requirements of NK Cell Responses to Viral Infection

In recent years, the field of immunometabolism – the study of how specific changes in cellular metabolism regulate the function of diverse immune cell types—has grown exponentially. Several in vitro studies have examined the metabolic regulation of natural killer (NK) cells, which are first responders for viral infection and malignant transformation; however, much less is known regarding the role of metabolism in directing NK cell responses in vivo, such as during viral infection. In order to examine how NK cell antiviral function is regulated in vivo, we used a wellcharacterized infection with murine cytomegalovirus (MCMV) to assess NK cell cytokine production, proliferation, and killing. Two treatments were used to manipulate major metabolic pathways: a drug model to examine the role of glycolytic metabolism, and a genetic model to examine the role of oxidative metabolism. We found that treatment with the glucose metabolism inhibitor 2-deoxy-ᴅ-glucose (2DG) impaired both mouse and human NK cell cytotoxicity following priming in vitro. Similarly, MCMV-infected mice treated with 2DG had impaired clearance of NK-specific targets in vivo, which was associated with higher viral burdens and increased susceptibility to infection on the C57BL/6 background. These effects could be reversed by pre-treatment with IL-15, which alters NK cell metabolism and metabolic requirements for activation. To interrogate the role of oxidative metabolism on NK cell function, we examined responses to MCMV in mice with an NK-specific deletion of Cox10, a nuclear gene encoding a protein required for functional assembly of mitochondrial electron transport chain Complex IV. Cox10-deficient NK cells developed normally, retaining normal function, energy production, and oxygen consumption at baseline. However, they had a defect in proliferation when activated through the Ly49H receptor in vitro and in vivo. Ly49H recognizes an MCMV-encoded protein and mediates preferential expansion of the Ly49H+ NK cell population. The expansion defect in Cox10-deficient NK cells was associated with decreased mitochondrial production of reactive oxygen species and increased susceptibility to MCMV infection. Thus, we found that uninhibited glucose metabolism is required by NK cells for maximal cytotoxic function, and that the oxidative pathway gene Cox10 is required by NK cells to proliferate optimally in response to MCMV infection. Our findings emphasize that metabolic pathways have specific interactions with different immune functions, and further develop methods to investigate metabolic regulation of immune cells in physiological contexts