The mechanism of K cell (antibody-dependent) cell mediated cytotoxicity II. Characteristics of the effector cell and morphological changes in the target cell

K cells share certain physical characteristics with T cells. This has made it possible to apply standard cell purification techniques to be used for the enrichment of K cells. This has in turn enabled time lapse studies to be carried out at low cell density. In addition, to the similar physical characteristics, K cells have a structure and movement similar to those of cytotoxic T cells. K cell cytotoxicity does no apparent damage to the K cell and each K cell is able to kill more than one target cell. Analysis of time lapse films of cytotoxicity of mouse P815 mastocytoma cells directly confirms three inferences on the mechanism of target cell death suggested by the kinetic data in the previous paper: contact itself does not appear to damage the target cell; target cell death usually begins within 15 min of K cell contact; cell death is an explosive event with zeiosis ‘boiling' of the cytoplasm. This phenomenon is similar to that observed with T cell cytotoxicity and quite different to changes seen during lysis by antibody and complement. Analysis of films of cytotoxicity of human MRC5 cells which are glass adherent has shown that the K cell is in close apposition to the nucleus within 1 min of the first cytoplasmic changes (shrinkage).