Natural killer cells

Abstract

Natural killer (NK) cells were described in the 1970s as large granular lymphocytes exhibiting “natural cytotoxicity” against several types of tumor cells. Significant progress has been made since then in the dissection of additional functional traits of NK cells. By their cytotoxic potential, they can kill many more types of cells than tumor cells, for example, virus-infected cells and several types of activated immune cells. To carry out these functions, and to discriminate target cells from nonactivated “normal” cells, NK cells are equipped with a molecular detection system that includes a variety of cell surface-activating and inhibitory receptors. Activating NK cell receptors can detect the presence of ligands on cells in “distress,” such as stress-induced self-ligands.