TUMOR-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, wer e 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 mu M prostaglandin E (2) (PGE(2)), which was ineffective at lower doses. Moreover, the O-2( -) production was slightly reduced by the phosphodiesterase type TV (P DE TV) inhibitor RO 20-1724, When PGE(2) and RO 20-1724 were added tog ether to TNF-triggered neutrophils they caused a marked synergistic in hibition 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) , PK, RO 20-1724) down-regulate the capacity of adherent neutrophils t o mount the respiratory burst in response to TNF. Consistent with this interpretation, PGE(2) and RO 20-1724 increased the intracellular lev els of cAMP displaying synergistic activity. Moreover, the membrane-pe rmeable analogue of cAMP, dibutyryl cAMP, was found to inhibit the TNP -induced O-2(-) production in a dose-dependent manner. As all the afor ementioned cAMP-elevating agents did not affect the O-2(-) production in response to phorbol myristate acetate, they appear to act by interf ering with the assembly of the O-2(-)-generating NADPH oxidase complex rather than by directly inhibiting the activity of already working ox idase complex, In conclusion, taking into account the TNF capacity to promote PGE(2) formation at sites;If inflammation, our observations su ggest the existence of a negative PGE(2)-dependent feed-back, potentia lly capable of controlling the neutrophil response to TNF and suscepti ble to amplification by PDE IV-inhibiting compounds.