Fig. 4

Blocking of antifibrinolytic activity by anti-plasminogen activator-1 antibody. Wild-type porcine endothelial cells were stimulated with 20% human serum for 2 hr and 24 hr, then incubated with serum-free medium for 24 hr. The conditioned medium was then harvested. Medium samples were either assayed without antibody for fibrinolytic activity (stippled bars), or incubated with 15 nM anti-plasminogen activator-1 antibody (filled bars) for 15 min at room temperature before being assayed. Medium blocked with plasminogen activator-1 antibody demonstrated fibrinolytic activity, suggesting the presence of active plasminogen activator inhibitor-1 in the medium. Medium exposed to human serum for 24 hr before blocking had 44% less fibrinolytic activity than the medium exposed for 2 hr. Increases in antifibrinolytic activity in response to stimulation with human antibody and complement were at least partly attributable to an increase in plasminogen activator inhibitor-1 production and secretion. The amount of plasminogen activator inhibitor-1 secretion increased with a longer exposure to human serum.