Fig. 2

Schematic of NK cell functions. a In normal cells, MHC class I molecules can engage inhibitory receptors on NK cells that can outnumber and override activating receptors, preventing NK-mediated cytotoxicity. b In malignant cells, downregulation of MHC class I molecules can result in the absence of NK inhibitor receptor engagement, resulting in NK-mediated cytotoxicity. c In cases where tumor cells retain expression of MHC class I molecules, NK cytotoxicity can still be induced through the upregulation of stress-induced activation ligands that can bind activation receptors on NK cells. d In instances when target cells are opsonized by antibodies, NK cells can exhibit ADCC by detecting antibodies on the target cell through the low-affinity Fcγ CD16 receptor. The outcome of the NK cell response is determined by the amount of activating versus inhibitory receptors on the NK cell surface