Stimulus interactions in release of superoxide anion (O2-) from human neutrophils. Further evidence for multiple pathways of activation.

A wide variety of agents stimulate superoxide anion (O2-) release from human neutrophils. To determine whether the same or different cellular pathways are utilized, neutrophils were stimulated to release O2- with combinations of f-Met-Leu-Phe (FMLP) (10(-7)M), C5a (25 nM), Con A (100 micrograms/ml), arachidonic acid (100 microM), and PMA (1 microgram/ml). These concentrations produced maximal O2- production when used alone. A synergistic response was observed when Con A was used in combination with FMLP or C5a. This response was twice the expected release in cytochalasin B-treated cells and three to five times the expected release in untreated cells. Additional studies showed that synergism was dependent upon the simultaneous presence of both agents. Additive O2- responses were observed when either FMLP, Con A, or C5a was tested in combination with arachidonic acid and when FMLP and C5a were tested together. When PMA was tested with C5a, FMLP, or Con A, a nonadditive O2- response resulted, whereas mixtures of PMA and arachidonic acid resulted in a less than additive response. These contrasting results using different soluble stimuli in combination suggest that multiple pathways exist for the stimulation of neutrophil O2- release, with some stimuli being totally independent of each other (possibly activating separate pools of oxidase), while other stimuli show cooperative effects on oxidase activation.