Activation of NADPH-oxidase by arachidonic acid involves phospholipase A2 in intact human neutrophils but not in the cell-free system

The mechanism involved in the stimulation of NADPH-oxidase by arachidonic acid (AA) in intact human neutrophils was studied and compared with that involved in a cell-free system. 3H]-AA was released from pre-labeled cells upon AA stimulation, and phospholipase A2 inhibitors reduced in parallel the release of 3H]-AA and superoxide. Cyclooxygenase, lipoxygenase or protein kinase inhibitors failed to affect either response. In a cell-free system, no release of 3H]-AA was observed after AA addition, whereas NADPH-oxidase was activated; the generation of superoxide was not inhibited by phospholipase inhibitors and was not initiated by adding phospholipase A2 to the preparation. Thus AA stimulates NADPH-oxidase through a phospholipase A2 mediated pathway in intact cells, but activates the oxidase independent of phospholipase A2 in a broken cell system, suggesting distinctive mechanisms of activation for each system.