Natural killer group 2 member D receptor–ligand axis (NKG2D axis)

The Natural killer group 2 member D (NKG2D) receptor–ligand axis is a fundamental immune surveillance system that facilitates the detection and elimination of stressed, infected, or malignant cells [1][2]. The NKG2D receptor, encoded by the KLRK1 gene, is a type II transmembrane C-type lectin-like activating receptor constitutively expressed on natural killer (NK) cells and CD8+ T cells [1][3]. It recognizes a diverse set of induced-self ligands, including MHC class I polypeptide-related sequences A and B (MICA and MICB) and UL16-binding proteins (ULBP1-6), which are typically upregulated under conditions of cellular stress such as DNA damage or viral infection [2][4]. In the context of oncology, tumors frequently employ immune evasion strategies by proteolytically shedding these ligands from the cell surface; the resulting soluble ligands (sMICA/B) act as decoys that downregulate NKG2D expression and impair cytotoxic function [5]. Conversely, dysregulation of this axis is implicated in autoimmune and inflammatory disorders, where chronic activation leads to inappropriate tissue damage [6]. Therapeutic strategies targeting this axis include NKG2D-based CAR-T therapies and shedding-inhibitors for cancer, as well as antagonistic antibodies for treating inflammatory conditions like Crohn's disease [2][7]. Sources: [1] UniProt P26718; [2] PMID: 30046154; [3] PMID: 21737067; [4] PMID: 11491521; [5] PMID: 29590618; [6] PMID: 25108024; [7] ClinicalTrials.gov NCT01203631.

Other names

KLRK1CD314Natural killer group 2 member DMICA/B-NKG2D pathwayULBP-NKG2D pathwayKiller cell lectin like receptor K1

The axis is targeted through multiple modalities: antagonistic monoclonal antibodies block the NKG2D receptor to reduce inflammation in autoimmune diseases; CAR-T or CAR-NK cells are engineered to express the NKG2D receptor to target ligand-positive tumor cells; and antibodies targeting the alpha-3 domain of MICA/B prevent proteolytic shedding, thereby maintaining high surface ligand density for immune recognition.