A sensitive assay, specific for endothelial cell type plasminogen activator inhibitor in blood plasma

A polyclonal antibody raised against plasminogen activator (PA-)inhibitor from endothelial cells fully precipitates the PA-inhibitor in endothelial cell conditioned medium but only a part of the PA-inhibitory activity in blood plasma. This indicates that the PA-inhibitory activity in blood plasma is not due to a single inhibitory component. Performing the assay for PA-inhibitory activity in plasma both in the presence and absence of saturating concentrations of anti-endothelial cell PA-inhibitor antibodies, allows the determination of endothelial cell type PA-inhibitor in plasma. The assay gives a linear dose-response curve of amount of plasma added versus t-PA neutralised. Values for endothelial cell type PA-inhibitor in plasma of a group of 20 healthy individuals are in the range of 0.0-16.8 IU/ml and are not normally distributed (median value 3.0 IU/ml). This method also reveals a second, so far unidentified, PA-inhibitory component in human plasma.