title: Natural killing and antibody-dependent cellular cytotoxicity are mediated by different mechanisms and by different cells.
abstract: Natural killing (NK) in humans, as well as in other species, has been shown to be specific for antigenic determinants present on the surfaces of a variety of tumor cells. Physical separation of NK cells from K cells, which mediate antibody-dependent cellular cytotoxicity (ADCC), has not been successful; however, there is indirect evidence suggesting that these activities are distinct. To further study the relationship between NK and K cells, competitive inhibition techniques were employed. NK cells can be blocked via two mechanisms: 1) by direct inhibition with NK-sensitive tumor cells binding to NK receptor sites present on the effector cells and 2) by steric inhibition resulting from the binding of antibody-coated cells to the FcR on the effector cells. K cells, however, lack the NK receptor site(s) but are FcR+, and can therefore be blocked only by antibody-coated cells. We therefore postulate that NK and K cells are two separate lymphoid populations. NK cells bear receptor site(s) for NK determinants and FcR, whereas K cells bear only FcR.
mesh_terms: D000328:Adult; D000920:Antibody-Dependent Cell Cytotoxicity; D001667:Binding, Competitive; D002460:Cell Line; D002469:Cell Separation; D000939:Epitopes; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology*
chemical_list: D000939:Epitopes