INCREASED LEUCOATTRACTANT BINDING AND REVERSIBLE INHIBITION OF NEUTROPHIL MOTILITY MEDIATED BY THE PEROXIDASE H2O2 HALIDE SYSTEM - EFFECTS OF ASCORBATE, CYSTEINE, DITHIOTHREITOL, LEVAMISOLE AND THIAMINE

Abstract

Human blood neutrophils manifested markedly decreased motility following exposure to the horseradish peroxidase (HRP)/H2O2 per halide system in vitro. These cells were protected from this inhibitory effect (of the HRP/H2O2 per halide system) by inclusion of concentrations in the reaction system of ascorbate, cysteine, levamisole and thiamine which stimulate neutrophil migration and inhibit activity of the HRP/H2O2 per halide system. The reversible nature of the oxidative inhibition of migration was demonstrated by exposing neutrophils to the HRP/H2O2 per halide system for 15 min followed by washing to remove the components of the peroxidative system and subsequent addition of ascorbate, cysteine, levamisole, thiamine and the reducing agent, dithiothreitol. Neutrophils so treated completely recovered normal or increased motility induced by the leukoattractants endotoxin-activated serum or synthetic chemotactic tripeptide F-Met-Leu-Phe. This reversible loss of migratory responsiveness following exposure of neutrophils to the HRP/H2O2 per halide system was not associated with decreased cell viability of adherence. However, membrane oxidation was accompanied by increased uptake of radiolabeled F-Met-Leu-Phe and degranulation. The increased leukoattractant uptake was decreased by ascorbate, levamisole and thiamine. These agents also prevented oxidation of the neutrophil membrane by the HRP/H2O2 per halide system as measured indirectly by inhibition of iodination.