Natural killer cell

A lymphocyte of the innate immune system that kills infected or cancerous cells without prior antigen-specific sensitization. It integrates activating and inhibitory signals to distinguish stressed cells from healthy ones.

Missing-self hypothesis: The idea that natural killer cells attack cells displaying unusually low levels of self MHC class I molecules. Reduced MHC class I removes inhibitory signals that normally protect healthy cells from NK-cell attack.
Lymphocyte: A white blood cell involved in adaptive or innate immune defense. Natural killer cells are lymphocytes, but they do not require antigen-specific priming to kill.
Natural killer cell therapy: Cancer treatment strategies that use natural killer cells to attack malignant cells. Therapies harness NK-cell cytotoxicity, sometimes modifying or expanding cells before infusion.
Natural killer T cell: An innate-like T cell with a T-cell receptor that recognizes lipid antigens presented by CD1d. Despite its name, this cell is a distinct T-cell lineage rather than a conventional NK cell.
Natural killer cell receptor: A surface protein that helps a natural killer cell detect activating or inhibitory signals. The combined receptor signals determine whether an NK cell spares or attacks a target.
Innate immunity: The fast-acting immune defenses that recognize broad signs of infection or tissue damage. NK cells provide cellular killing within this rapid, broadly targeted defense system.
Chimeric antigen receptor natural killer cell: A natural killer cell engineered with a receptor that recognizes a chosen tumor target. CAR engineering adds target-specific recognition to NK cells’ existing killing machinery.
Group 1 innate lymphoid cell: An innate lymphoid-cell category that includes natural killer cells and related cytokine-producing cells. NK cells belong to this broader family, which shares innate lymphoid development.
Perforin: A cytotoxic protein that forms pores in target-cell membranes. NK cells release perforin to enable delivery of granzymes into target cells.
Adaptive immunity: Immune defense based on antigen-specific lymphocytes and immunological memory. Unlike adaptive cytotoxic lymphocytes, NK cells can kill without prior antigen-specific sensitization.

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