Quantitative and temporal characterization of the extracellular H2O2 pool generated by human neutrophils

The extracellular H2O2 concentration surrounding stimulated human neutrophils was continuously quantitated with a sensitive, H2O2-detecting electrode. Following stimulation of neutrophils with phorbol myristate acetate, opsonized zymosan particles, or N-formyl-Met-Leu-Phe, the extracellular H2O2 concentration rapidly increased and maintained steady state conditions before falling to undetectable levels in a manner that was dependent on the triggering agent used. Total extracellular H2O2 accumulation for each stimulus was quantitated as the integral of the H2O2 concentration with respect to time. H2O2 accumulation in the extracellular milieu was unaffected by the addition of superoxide dismutase, whereas exogenous catalase or myeloperoxidase completely consumed the released H2O2. Analysis of H2O2 metabolism by neutrophils revealed that stimulus-dependent differences in the size of the extracellular H2O2 pool may be partially attributable to differences in hypochlorous acid generation by the H2O2, myeloperoxidase, chloride system. Finally, both the concentration of H2O2 in the extracellular space and its utilization by myeloperoxidase could be diminished in the presence of an extracellular target cell. These data indicate that the ability of a triggering agent to stimulate the neutrophil to generate H2O2 and release myeloperoxidase, coupled with the characteristics of a target cell population, control H2O2 metabolism in effector-target cell interactions.