Tumour necrosis factor alpha-induced oxidative burst in neutrophils adherent to fibronectin: effects of cyclic AMP-elevating agents

Human neutrophils, plated on fibronectin-coated polystyrene wells, were found to exhibit a prolonged production of superoxide anion (O 2 - ) in response to tumour necrosis factor-alpha (TNF). The TNF-triggered O 2 - production was significantly reduced by 10 μM prostaglandin E 2 (PGE 2 ), which was ineffective at lower doses. Moreover, the O 2 2 production was slightly reduced by the phosphodiesterase type IV (PDE IV) inhibitor RO 20-1724. When PGE 2 and RO 20-1724 were added together to TNF-triggered neutrophils they caused a marked synergistic inhibition of O 2 - production. The action of PGE 2 could be mimicked by forskolin (FK), a well-known direct activator of adenylate cyclase. These results suggest that cyclic AMP (cAMP)-elevating agents (PGE 2 , FK, RO 20-1724) down-regulate the capacity of adherent neutrophils to mount the respiratory burst in response to TNF. Consistent with this interpretation, PGE 2 and RO 20-1724 increased the intracellular levels of cAMP displaying synergistic activity. Moreover, the membrane-permeable analogue of cAMP, dibutyryl cAMP, was found to inhibit the TNF-induced O 2 - production in a dose-dependent manner. As all the aforementioned cAMP-elevating agents did not affect the O 2 - production in response to phorbol myristate acetate, they appear to act by interfering with the assembly of the O 2 - -generating NADPH oxidase complex rather than by directly inhibiting the activity of already working oxidase complex. In conclusion, taking into account the TNF capacity to promote PGE 2 formation at sites of inflammation, our observations suggest the existence of a negative PGE 2 -dependent feed-back, potentially capable of controlling the neutrophil response to TNF and susceptible to amplification by PDE IV-inhibiting compounds.