Measurements of the concentration of free plasminogen activator inhibitor (PAI-1) and its complex with tissue plasminogen activator in human plasma.

A new assay system to measure free plasminogen activator inhibitor (PAI-1) and its complex with tissue plasminogen activator (t-PA) was developed. A silicone piece coupled with anti-PAI-1 monoclonal antibody was incubated with human plasma or human plasma which had previously been incubated with t-PA in order to convert all the free PAI-1 to t-PA-PAI-1 complex. After incubation, the amounts of t-PA bound on each silicone piece were measured by enzyme immunoassay. The amounts of t-PA on a silicone piece incubated with plasma represent the amounts of t-PA-PAI-1 complex in the original plasma, and the amounts of t-PA on a silicone piece incubated with plasma previously added with t-PA represent total PAI-1 (the complex plus free PAI-1). Using the technique, the concentration of t-PA-PAI-1 complex seems to increase with age and there was a good correlation between the concentration of free PAI-1 and t-PA-PAI-1 complex in the plasma.