Thromboxane A2 Mediates Augmented Polymorphonuclear Leukocyte Adhesiveness

Abstract

We examined the role of prostaglandins and thromboxanes as mediators of plasma-dependent increased polymorphonuclear leukocyte adhesiveness induced by Escherichia coli lipopolysaccharide. The cyclo-oxygenase inhibitors—indomethacin and d,l-6-chloro-α-methyl-carbozole-2-acetic acid (R020-5720)—reduced lipopolysaccharide-induced adherence of polymorphonuclear leukocytes by 74 and 62%, respectively. In addition, inhibitors of thromboxane synthetase—imidazole, 9,11-azoprosta-5,13-dienoic acid, and 1-benzylimidazole—suppressed the stimulation of adherence by 31, 66, and 83%, respectively. Exogenous prostaglandins E₁, E₂, and F₂α did not increase polymorphonuclear leukocyte adherence, nor were they detected in significant quantities in supernates of polymorphonuclear leukocytes exposed to lipopolysaccharide. However, inhibitors of both cyclo-oxygenase and thromboxane synthetase reduced increases in adherence induced by arachidonic acid (10 μg/ml), suggesting that lipopolysaccharide-mediated increases in adherence were due to an arachidonic acid product other than prostaglandin E₂ or F₂α. 8,11,14-Eicosatrienoic acid, a precursor of monoenoic prostaglandins, did not enhance polymorphonuclear leukocyte adhesiveness. We next demonstrated lipopolysaccharide-stimulated generation, by polymorphonuclear leukocytes, of a labile, low molecular weight, dialyzable substance capable of enhancing the adherence of unstimulated leukocytes. In parallel experiments, a 10-fold increase in immunoreactive thromboxane B₂ over basal levels was detected after exposure of leukocytes to lipopolysaccharide. The inhibition of lipopolysaccharide enhancement of adherence by specific rabbit antibodies to thromboxane B₂ strongly supported a primary role for thromboxane A₂ as the mediator of the observed increases in adherence. Lipopolysaccharide-stimulated purified platelets did not increase leukocyte adherence, whereas thrombin-stimulated platelets did increase adherence. These studies suggest that lipopolysaccharide stimulates polymorphonuclear leukocytes to produce thromboxane A₂, which enhances their adhesiveness to nylon.