KLRK1 and viral infectious disease: The natural killer group 2 member D (NKG2D) receptor and its ligands (NKG2DLs) are key components in the innate immune control of viral infections and cancers.12 NKG2D is an activatory receptor expressed by natural killer (NK) cells, γδ T cells, CD8+ T cells, and some CD4+ T cells, and can bind to eight different NKG2DLs, major histocompatibility complex (MHC)-class-I-polypeptide-related sequence (MIC) A and MICB, and UL16-binding protein 1–6.13