title: Polymorphonuclear leukocyte adhesion to endothelial cells is inhibited by resting platelets.
abstract: The effect of human platelets on the adhesion of polymorphonuclear leukocytes (PMNs) to cultured endothelial cells was investigated. Resting platelets inhibited the adhesion of PMNs stimulated by N-formyl-methionyl-leucyl-phenylalanine (fMLP), leukotriene B4 (LTB4), and tumor necrosis factor-alpha (TNF-alpha). Platelets similarly inhibited PMN adhesion induced by endothelial cell activation with TNF-alpha. The inhibitory effect depended on platelet number, was not associated with detectable platelet activation, and was also exerted by paraformaldehyde-fixed platelets. Moreover, supernatants of U46619- or thrombin-stimulated platelets were ineffective, thus excluding a role for constituents released as a result of the platelet-release reaction. Strong inhibition of PMN adhesion was exerted by platelet lysates. The inhibitory activity associated with lysates was sedimentable, heat sensitive, and not dialyzable through a membrane with a molecular-weight cutoff of 8,000; it was directed toward PMNs and was not due to cytotoxic effects or a general inhibition of PMN responsiveness to stimulation, since enzymatic release from activated PMNs was unaffected by platelet lysates. Finally, the activity was not prevented by specific adenosine inhibitors and anti-P-selectin monoclonal antibody. These data suggest that resting platelets can exert an inhibitory effect on PMN adhesion to the vessel wall during inflammatory and thrombotic conditions.
mesh_terms: D000241:Adenosine / Q000502:physiology; D000818:Animals; D001792:Blood Platelets / Q000502:physiology*; D002417:Cattle; D002448:Cell Adhesion; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000502:physiology*; D006801:Humans; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000502:physiology*; D019007:P-Selectin; D010980:Platelet Membrane Glycoproteins / Q000502:physiology
chemical_list: D019007:P-Selectin; D010980:Platelet Membrane Glycoproteins; D009240:N-Formylmethionine Leucyl-Phenylalanine; D000241:Adenosine