Phospholipase D and Priming of the Respiratory Burst by H2O2 in NR8383 Alveolar Macrophages

Previous investigation showed that preincubation within a range of nontoxic H(2)O(2) concentrations enhanced subsequently stimulated superoxide production by rat alveolar macrophages in response to various stimuli. In the present study, the NR8383 rat alveolar macrophage cell line was used to further investigate the priming effect of H(2)O(2). Using nitroblue tetrazolium, which formed an insoluble formazan when reduced by superoxide, modulation of the respiratory burst was visualized in a cell population exposed to a concentration gradient of H(2)O(2) before stimulation. This model system illustrates how H(2)O(2) may constitute a signaling molecule for a feed-forward regulation of the respiratory burst during inflammation. n-Butanol, which allows consumption of phosphatidic acid by the transphosphatidylation reaction, and propanolol, which inhibits phosphatidic acid phosphohydrolase, were used to investigate the possible involvement of phospholipase D in this phenomenon. These two agents were found to inhibit the basal adenosine diphosphate-stimulated respiratory burst. Inhibition of the H(2)O(2)-enhanced respiratory burst was equally or slightly less effective when expressed as percentage of controls. Furthermore, phospholipase D was not activated by H(2)O(2) concentrations that enhance superoxide production. Thus, phospholipase D does not mediate the enhancement of the respiratory burst by H(2)O(2), although it may be activated by high concentrations of this hydroperoxide.