Natural killer activating receptor (NKR)

Natural killer (NK) activating receptors are a heterogeneous group of signaling proteins expressed on the surface of Natural Killer T (NKT) cells and NK cells that mediate the recognition and elimination of stressed, infected, or transformed cells (Vivier et al., 2011, Nature Immunology). On NKT cells, these receptors—most notably NKG2D (KLRK1), DNAM-1 (CD226), and the natural cytotoxicity receptors (NCRs) such as NKp46—function independently or in synergy with the semi-invariant T-cell receptor (TCR) to trigger cytotoxic granule release and cytokine production (Godfrey et al., 2004, Nature Reviews Immunology). These receptors recognize a variety of ligands, including MHC class I-like molecules (MICA/B), which are often upregulated on tumor cells or during viral infections (Lanier, 2005, Annual Review of Immunology). In therapeutic contexts, these receptors are targeted to overcome immune evasion in cancer, where tumors often downregulate activating ligands or induce receptor internalization. Current pharmacological approaches include bispecific killer cell engagers (BiKEs) and chimeric antigen receptor (CAR)-NKT cells designed to potently activate these pathways against specific malignancies (Rotolo et al., 2018, Frontiers in Immunology).

Other names

NK cell activating receptorActivating NK receptorNatural cytotoxicity receptorNCRNKG2DNKp46NKp30NKp44DNAM-1CD226KLRK1NCR1NCR2NCR3CD16FCGR3A

Engagement of activating receptors triggers the immunoreceptor tyrosine-based activation motif (ITAM) or YINM-mediated signaling pathways, leading to NKT cell degranulation, release of perforin and granzymes, and secretion of pro-inflammatory cytokines like IFN-gamma (Vivier et al., 2011, Nature Immunology).