Natural killer cells
Large granular lymphocytes that attack and destroy certain virus-infected and tumor cells.
Natural killer (NK) cells are a relatively small population (5–10% of circulating lymphocytes) of large granular lymphocytes that variably express CD2 and the IL-2 receptor (β subunit), and almost always CD16 (the FcγRIII receptor). Although they are similar to T cells in many respects, NK cells are bone marrow derived, and unlike B and T cells there is no somatic rearrangement of NK cell receptors. Thus NK cells still are produced by athymic and recombinase deficient mice. NK cells bear Fas ligand (FasL) on their surface and thus they induce death by apoptosis in Fas-bearing target cells. Also NK cells are always cytotoxic, because they contain many granules full of perforin and granzymes. Via there FcγRIII NK cells can also mediate antibody-dependent cell-mediated cytotoxicity (ADCC) of antibody decorated target cells. ADCC occurs when a target cell,...