The combination of Type i IFN, TNF-α, and cell surface receptor engagement with dendritic cells enables nk cells to overcome immune evasion by dengue virus

Clinical studies have suggested the importance of the NK cell response against dengue virus (DenV), an arboviral infection that afflicts >50 million individuals each year. However, a comprehensive understanding of the NK cell response against dengueinfected cells is lacking. To characterize cell-contact mechanisms and soluble factors that contribute to the antidengue response, primary human NK cells were cocultured with autologous DenV-infected monocyte-derived dendritic cells (DC). NK cells responded by cytokine production and the lysis of target cells. Notably, in the absence of significant monokine production by DenV-infected DC, it was the combination of type I IFNs and TNF-α produced by DenV-infected DC that was important for stimulating the IFN-γ and cytotoxic responses of NK cells. Cell-bound factors enhanced NK cell IFN-γ production. In particular, reduced HLA class I expression was observed on DenV-infected DC, and IFN-γ production was enhanced in licensed/educated NK cell subsets. NK-DC cell contact was also identified as a requirement for a cytotoxic response, and there was evidence for both perforin/granzyme as well as Fas/Fas ligand-dependent pathways of killing by NK cells. In summary, our results have uncovered a previously unappreciated role for the combined effect of type I IFNs, TNF-α, and cell surface receptor-ligand interactions in triggering the antidengue response of primary human NK cells.