Spontaneous tumor cytolysis mediated by inflammatory neutrophils: dependence upon divalent cations and reduced oxygen intermediates

The role of divalent cations and reactive products of the respiratory burst were investigated in spontaneous tumor lysis mediated by inflammatory neutrophils (PMNs). Murine peritoneal PMNs, obtained five hours after intraperitoneal injection of bacteria, conjugated and lysed teratocarcinoma cells in chromium release and single-cell cytotoxicity assays. The presence of extracellular magnesium was required and was sufficient for tumor cell binding to PMNs. Postbinding lytic events depended upon the simultaneous presence of extracellular calcium and magnesium. Catalase and superoxide dismutase inhibited postbinding lytic events, indicating that production of reduced oxygen moieties was important. Scavengers of hydroxyl radicals could inhibit tumor cell binding, but none could affect postbinding lytic events. Neither could inhibitors of myeloperoxidase decrease tumor lysis. The ability of conjugating PMNs to lyse their bound targets correlated with their reduction of nitro blue tetrazolium (NBT). Optimal concentrations of phorbol myristate acetate (PMA) markedly increased the NBT positivity of PMNs and the killing of bound tumor cells. Even with optimal stimulation of the respiratory burst, however, there was still a significant number (19%) of bound targets that escaped lysis, suggesting active resistance to oxygen-mediated tumor cell injury.