NKG2CD94

NKG2C–CD94 is a heterodimeric receptor complex expressed on natural killer (NK) cells and a subset of Vδ1 γδ T cells. The complex is formed by the non‑covalent association of the type II transmembrane protein NKG2C with the type I transmembrane protein CD94. Both subunits are encoded by genes located in the leukocyte receptor cluster on chromosome 12q24. There is also a closely related inhibitory counterpart, NKG2A–CD94, which shares the CD94 partner but contains the NKG2A subunit instead of NKG2C. The NKG2C–CD94 complex is an activating receptor; it signals through the adaptor protein DAP12 that contains ITAM motifs. Upon ligand engagement, DAP12 is phosphorylated, leading to downstream signaling cascades that promote cytotoxic granule exocytosis and the production of inflammatory cytokines such as interferon‑γ.

The primary ligands for NKG2C–CD94 are non‑classical MHC class I molecules of the HLA‑E family. HLA‑E presents peptides derived from the leader sequences of other MHC class I molecules, and its surface expression is influenced by TAP transporter activity. The interaction between HLA‑E and NKG2C–CD94 provides a measure of cellular health; cells that downregulate classical MHC class I expression (for example, infected or transformed cells) may display altered HLA‑E peptide presentation, which can be detected by NK cells via this receptor. In addition to viral infection and tumor surveillance, the NKG2C–CD94 pathway has been implicated in the immune response against CMV, where expansion of NKG2C+ NK cells is a characteristic feature of CMV seropositive individuals.

Genetic variation in the NKG2C gene, including a common deletion polymorphism that removes both NKG2C and the adjacent NKG2E gene, influences individual immune repertoire and disease susceptibility. Carriers of the deletion have reduced numbers of NKG2C+ NK cells and may have altered responses to infections such as HIV, hepatitis B, and SARS‑CoV‑2, as well as modified transplant outcomes in hematopoietic cell transplantation. Because the receptor serves as a bridge between innate and adaptive immunity, it is an active target in both basic research and clinical studies of immunotherapy, infectious diseases, and transplant medicine.