Polymorphonuclear leukocytes regulate the plasminogen-activating system of cultured endothelial cells

Exposure of bovine pulmonary artery endothelial cells (BEC) to polymorphonuclear leukocytes (PMN) (1 x 10(6)/ml) stimulated by opsonized zymosan (OZ-PMN) decreased plasminogen activator (PA) activity in conditioned medium by as much as 98% as compared to controls. Unstimulated PMN (U-PMN) (1 x 10(6)/ml), after an initial enhancement, decreased PA activity 95%. Low concentrations of U-PMN and OZ-PMN enhanced and high concentrations depressed PA activity. The decline in PA activity was not associated with an increased endothelial cell injury. The suppression of PA activity by OZ-PMN was associated with a 7-fold increase in activity of PA inhibitor 1 (PAI-1). PMN did not affect PA after its secretion, suggesting that modulation of endothelial cells by PMN changes the net activities of PA and PAI-1 in the conditioned medium.