KLRK1 and neoplasm: The activating receptor NKG2D on NK cells recognize the MHC class I-related surface proteins MICA and MICB as well as the UL-16-binding proteins (ULBPs; ULBP1-6), which are often upregulated in e.g. tumor cells countermanding any inhibitory signals and inducing NK cell-mediated cytotoxicity (45, 46).