Adenosine inhibits platelet-activating factor, but not tumour necrosis factor-alpha-induced priming of human neutrophils.
Regulation of the respiratory burst and its priming by recombinant human tumour necrosis factor-alpha (rhTNF-alpha) and platelet-activating factor (PAF) were investigated in human polymorphonuclear leucocytes (PMN). Adenosine (0.1-10 microM) pretreatment of PMN concentration-dependently inhibited the superoxide anion generation (O2-) in response to formyl-methionyl-leucyl-phenylalanine (FMLP). The priming by PAF (1 microM) for an increased O2- generation by FMLP-stimulated PMN was completely blocked by adenosine pretreatment. In contrast, rhTNF-alpha-induced priming was unaffected by adenosine. In addition, the direct stimulation of PMN O2- by rhTNF-alpha was also unaffected by adenosine as was rhTNF-alpha-induced PAF synthesis. FMLP-induced PAF synthesis was reduced by adenosine to a similar extent as the inhibition of the respiratory burst. Adenosine also inhibited PAF-, but not FMLP-induced increases in intracellular calcium in PMN. These findings indicate that short-term, direct stimulants (FMLP) or priming agents (PAF) are subject to modulation by the endothelial product adenosine, whereas the priming and direct stimulation of the respiratory burst by the longer-acting agent, rhTNF-alpha is unaffected. Moreover, differential inhibition of PMN activation by adenosine reveals important functional differences in the signalling mechanisms initiated by PAF, FMLP and rhTNF-alpha.
Department of Physiology, University of Melbourne, Parkville, Victoria, Australia.
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D000241:Adenosine / Q000494:pharmacology / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D006801:Humans; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors / Q000502:physiology*; D011994:Recombinant Proteins / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology / Q000502:physiology*
D010972:Platelet Activating Factor; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D013481:Superoxides; D000241:Adenosine; D002118:Calcium