Granule Exocytosis in a Cultured Human Natural Killer Cell-Rich Population Induced by K562 Target Cells and by PMA/A23187

Granule exocytosis in natural killer (NK) cells induced by K562 target cells and by PMA/A23187 was examined by measuring N-benzyloxycarboxy-L-lysine esterase activity. We obtained a cultured human NK cell-rich population containing around 90% of CD16+ cells by culturing peripheral blood mononuclear cells with mitomycin C-treated Daudi cells in the presence of IL-2. Granule exocytosis in the cultured NK cells was induced by K562 cells in a target/effector cell ratio-dependent manner. The granule exocytosis induced by K562 cells was inhibited neither by EGTA nor by TMB-8, an intracellular calcium antagonist, nor by a combination of these two reagents, while the exocytosis induced by PMA/A23187 was inhibited in a dose-dependent manner both by EGTA and by TMB-8. However, the cytotoxic activity of the cultured NK cells was inhibited by EGTA, suggesting that calcium is required not for the induction of granule exocytosis but for other steps including its requirement for the exertion of perforin activity.