Tumor necrosis factor alpha 'primes' the platelet-activating factor-induced superoxide production by human neutrophils: possible involvement of G proteins.

It has recently been demonstrated that very low concentrations of platelet-activating factor (PAF) and various cytokines can prime human neutrophils (PMN) to respond in an enhanced manner to subsequent agonistic stimulation. We were interested to ascertain whether superoxide generation by human PMN could be amplified by PAF following initial stimulation with tumor necrosis factor (TNF) and the effect of cholera and pertussis toxin on this process. PAF alone (0.1 pM-0.1 nM) failed to evoke any superoxide production; however, when PAF was added for 10 min to cells previously incubated for 50 min with 10 ng/ml TNF, superoxide production was significantly enhanced relative to that induced by TNF alone. Maximum amplification (+30%) was obtained with 10(-12) M PAF, this effect being completely abolished by BN 52021 and BN 52111, two structurally unrelated PAF antagonists. The PAF antagonists also decreased by 25% the superoxide production elicited solely by TNF, indicating that TNF-induced superoxide generation is partially mediated by a mechanism involving endogenous PAF. Pretreatment of the PMN with pertussis or cholera toxin reduced the amplification of superoxide production induced by PAF in TNF-stimulated PMN, implicating pertussis and cholera toxin-sensitive G-proteins in the amplification process.