Neutrophils may directly synthesize both H2O2 and O2 ? since surface stimuli induce their release in stimulus-specific ratios

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Abstract
Many stimuli induce neutrophils to undergo an oxidative burst and generate toxic oxygen metabolites. The major products are O2 − and H2O2, the latter being presumed to arise by spontaneous dismutation of the former. If H2O2 were indeed derived exclusively from released O2 − according to the equation 2O2 − + 2H+ → H2O2 + O2, one would expect that relationship to be reflected in the ratio of the two metabolites detectable in the extracellular mileu of stimulated neutrophils. A second corollary is that H2O2 should not form when cytochromec is present to scavenge O2 − before it can dismutate. Although H2O2 cannot be measured directly in the presence of cytochromec because it is consumed in reoxidizing reduced cytochromec, its presence can be detected indirectly by the ability of catalase to improve the apparent yield of reduced cytochromec. We found that the relative amounts of extracellular H2O2 and O2 − that could be measured in the environment of stimulated neutrophils varied with the stimulus and that catalase protected reduced cytochromec from H2O2 oxidation when some stimuli were used but not with others. For example, the ratio of O2 − to H2O2 produced by neutrophils exposed to PMA was about 2∶:1, the expected result if H2O2 were derived from O2 −. However when cytochalasin B was added to the cells before the stimulus, the yield of H2O2 was reduced but not the yield of O2 −. When cells were allowed to settle and spread on tissue culture plastic they produced equimolar amounts of O2 − and H2O2. Coating the plastic with IgG doubled cytochromec reduction without effecting H2O2. In contrast, coating with albumin reduced H2O2 without effecting cytochromec reduction. Soluble IgG aggregates induced production of mostly O2 − whereas immune complexes resulted in release of both metabolites. FMLP and A23187 were similar to the soluble IgG aggregates in their effects and induced release of proportionately more O2 − than H2O2. The addition of catalase to the cytochromec solution improved the yield of reduced cytochromec when PMA or IgG was used to stimulate the cells but not when FMLP was used. These and other data suggest that H2O2 release is not a linear function of the amount of O2 − generated and that either a variable fraction of O2 − spontaneously dismutates to H2O2 or the neutrophil NADPH oxidase, in a manner analogous to xanthine oxidase, is capable, under some circumstances, of producing H2O2 as well as O2 −. If the latter were true, the pathologic consequences of neutrophil activation would vary depending on whether O2 − was the primary product (chemotactic activation) or whether H2O2 was released as well (immune complex stimulation).