Hydrogen peroxide increases the phagocytic function of human neutrophils by calcium mobilisation

We have studied the effect of exogenous administration of hydrogen peroxide (H2O2) on phagocytic activity of human neutrophils. The treatment of cells with increasing concentrations of H2O2 evoke a significant elevation of phagocytic function assayed as phagocytic index, percentage and efficiency; and was similar to that induced by the calcium mobilising agonist formyl-methionyl-leucyl-phenylalanine (fMLP). This stimulatory effect was reduced by pre-treatment of neutrophils with catalase and abolished in neutrophils loaded with the intracellular calcium quelator dimethyl BAPTA. In the absence of extracellular calcium, treatment of cells with H2O2 resulted in a increase in [Ca2+](i) , indicating the release of calcium from intracellular stores. H2O2 abolished the typical calcium release stimulated by the physiological agonist fMLP, while depletion of agonist-sensitive calcium pools by fMLP was able to prevent H2O2-induced calcium release. We conclude that H2O2 induces calcium release from agonist-sensitive stores and consequently increase the phagocytosis process.