KLRK1 and neoplasm: NK cell function is triggered by the loss of the inhibitory receptor-mediated signalling when tumour cells downregulate the expression of MHC (major histocompatibility complex) class I. The simultaneous engagement of activating receptors, such as NKG2D, DNAM-1, and natural cytotoxicity receptors NKp30, NKp44, and NKp46 is required for the robust activation of NK cells and the NK cell-mediated killing of transformed cancer cells.