| NKp46, also termed NCR1 or CD335, is a type I transmembrane receptor of the immunoglobulin superfamily that functions as a major activating receptor on natural killer (NK) cells and is widely used as a lineage marker for NK cells across species. The receptor comprises an extracellular region with two Ig‑like domains that recognize pathogen‑derived and host‑encoded ligands, a single transmembrane segment containing a charged residue that mediates association with ITAM‑bearing adaptor molecules, and a short cytoplasmic tail without intrinsic signaling motifs. NKp46 associates with FcRγ and CD3ζ adaptors, and ligand engagement induces phosphorylation of their ITAMs, recruitment and activation of Src family kinases and Syk/ZAP‑70, and downstream propagation through LAT‑ and SLP‑76–centered complexes that connect to PLCγ, calcium mobilization, MAPK activation, and transcription factor programs controlling degranulation and cytokine production. NKp46 recognizes multiple viral and cellular ligands, including hemagglutinins and hemagglutinin‑neuraminidases from several enveloped viruses and stress‑induced or ER‑stress–related host ligands, and this binding triggers perforin/granzyme release and IFN‑γ secretion that contribute to clearance of infected or transformed target cells. Expression of NKp46 is high and relatively selective on NK cells and is also present on ILC1 and NCR⁺ ILC3 subsets and some γδ T cells, where NKp46 contributes to group 1 innate lymphoid cell effector functions and to innate lymphoid surveillance at barrier tissues. In murine systems, NKp46/Ncr1 controls TRAIL protein expression in NK cells and ILC1s and thereby regulates death receptor–mediated cytotoxicity against susceptible targets, linking NKp46 engagement to both granule exocytosis and TRAIL‑dependent killing pathways. NKp46 expression is modulated by cytokines, microenvironmental mediators, and metabolic cues, and downregulation of surface NKp46 by tumor‑ or infection‑related factors associates with impaired NK cell activation, whereas enforced or sustained expression supports enhanced killing capacity and cytokine output. NKp46 is detected on malignant NK and some T‑lineage lymphomas, where its presence serves as a diagnostic marker and identifies cells that retain NK‑type activating receptor machinery. The receptor is an attractive target for therapeutic engineering, as multifunctional NK cell engagers that bind NKp46 together with CD16 and tumor‑associated antigens induce strong NK activation and tumor cell lysis by coupling NKp46‑ITAM signaling with Fc‑ and antigen‑driven synapse formation. Across infection, cancer, and inflammatory settings, NKp46/NCR1 operates as a central activating module that translates ligand recognition on NK cells and related innate lymphoid cells into defined ITAM‑dependent signaling cascades, effector molecule regulation such as TRAIL, and cytotoxic and cytokine responses that shape innate immune surveillance and downstream adaptive immunity. |
