Phorbol myristate acetate-treated endothelium stimulates polymorphonuclear leukocyte adhesion and superoxide secretion.

The adherence of polymorphonuclear leukocytes (PMNLs) to the pulmonary vascular endothelium may contribute to acute lung injury. We studied the mechanism whereby treatment of bovine pulmonary artery endothelial cells with the potent inflammatory agent phorbol myristate acetate (PMA) stimulated the adherence and secretion of superoxide anion by human PMNLs. Treatment of endothelial cell monolayers with 100 ng/ml PMA resulted in a time-dependent increase in PMNL adherence to the endothelial cells. Treatment of endothelial cells with PMA or the less-lipophilic active phorbol ester 4-beta-phorbol 12,13-dibutyrate stimulated PMNL adherence in a dose-dependent manner, but the inactive phorbol ester 4-alpha-12,13 dideconoate had no effect on PMNL adherence. When formalin-fixed endothelial cells were treated with PMA, the increase in PMNL adherence was similar to that observed with unfixed endothelial cells. Treatment of fixed endothelial cells with 4-beta-phorbol 12,13 dibutyrate did not promote adherence. PMA-induced stimulation of PMNL adherence to endothelial cells was not eliminated by washing the PMA-treated endothelial cells, and the 4-hour conditioned medium obtained from PMA-treated endothelial cells also stimulated PMNL adherence to untreated endothelial cell monolayers PMNL adherence induced by PMA also stimulated the secretion of superoxide anion. Thus, PMA bound to the vascular endothelium will promote both PMNL adhesion and the secretion of reactive oxygen intermediates. Furthermore bound PMA rereleased from the endothelium can also stimulate PMNL adherence and superoxide anion secretion at a distant site.