Triggering of neutrophil cytotoxicity against an antibody-coated tumour target by TPA

The human erythroid myeloid leukaemia cell line K562 was used as target for human neutrophil cytotoxicity. Neutrophils demonstrated cytotoxicity against K562 only in the presence of a second stimulus, tetradecanoyl phorbol acetate (TPA), a result consistent with previous observations. We now demonstrate that antibody-coated K562 (using OKT9 and 345 monoclonal antibodies) are similarly only sensitive to neutrophils when TPA is added. The presence of both antibody and TPA in the cytotoxic assay resulted in significantly higher levels of cytotoxicity than in the absence of antibody; the result being consistent with a synergistic action between protein kinase C activation and Fc receptor perturbation in the neutrophil. The cytotoxicity against non-coated and antibody-coated targets was markedly inhibited, particularly against the former, by the protein kinase C inhibitor, 1-(5-isoquinoline-sulfonyl)-2-methyl piperazine (H-7). There were marked differences in the extracellular calcium dependency of the two types of cytotoxicity reactions. TPA-activated respiratory burst was unaffected by the presence of non-coated and OKT9-coated targets, whereas TPA-induced lysosomal enzyme release was significantly increased by non-coated targets and a further increase occurred in the presence of OKT9-coated K562