Determination of plasmin-α₂-antiplasmin complex in plasma samples by means of a radioimmunoassay

Immunization of a goat with partially reduced and S-carboxymethylated plasmin B-chain-alpha 2-antiplasmin complex resulted in a large population of antibodies with rather high specificity towards the complex. These antibodies do not react with plasminogen or plasmin in complex with other inhibitors than alpha 2-antiplasmin. However, they react fully with native alpha 2-antiplasmin, but a 200-fold higher concentration, as compared to plasmin-alpha 2-antiplasmin complex, is needed to obtain a similar displacement curve in a double-antibody radioimmunoassay. The results indicate a conformational change in the vicinity of the reactive site in alpha 2-antiplasmin, as a result of complex formation with plasmin. A method for determination of plasmin-alpha 2-antiplasmin complex in plasma has been elaborated using the described radioimmunoassay. About 1.5 mg plasmin-alpha 2-antiplasmin complex/l can be detected, which equals the condition when about 1% of the alpha 2-antiplasmin in plasma is in complex with plasmin. In normal individuals plasmin-alpha 2-antiplasmin complex could be detected only rarely. However, patient with acute processes, as evidenced by high fibrinogen levels, surgical patients postoperatively or patients with malignancy have often detectable levels.