Natural killer cell recognition system (NKCR)

Natural Killer (NK) cell recognition via missing-self and stress ligands is a fundamental immunological process used to identify and eliminate compromised cells. The 'missing-self' hypothesis describes how NK cells detect the downregulation of MHC class I molecules—a common evasion tactic by tumors and viruses—which otherwise provide inhibitory signals through receptors like Killer-cell Immunoglobulin-like Receptors (KIRs) (Kärre et al., 1986). Complementing this, 'stress ligands' such as MICA, MICB, and ULBPs are expressed by cells undergoing DNA damage or malignant transformation, binding to the activating receptor NKG2D to trigger NK cell-mediated lysis (Raulet, 2003). This recognition system is a critical target in cancer immunotherapy, where therapeutic strategies aim to either block inhibitory 'checkpoints' (e.g., using Monalizumab to block NKG2A) or enhance the visibility of stress ligands. Therapeutic success depends on overcoming tumor-driven resistance mechanisms, such as the proteolytic shedding of stress ligands which acts as a decoy for NK cells (Groh et al., 2002). Overall, this system balances inhibitory and activating signals to ensure precise immune surveillance while maintaining self-tolerance (Vivier et al., 2012).

Other names

Missing-self recognitionStress-induced ligand recognitionNK cell immunosurveillanceNKG2D-MICA/B axisKIR-HLA axisNK cell activation pathway

The system is targeted by blocking inhibitory receptors such as KIR and NKG2A to prevent 'missing-self' evasion or by engaging activating receptors like NKG2D to recognize stress-induced ligands on target cells.