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

Abstract

Immunization of a goat with partially reduced and S-carboxymethylated plasmin B-chain-α₂-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 α₂-antiplasmin. However, they react fully with native α₂-antiplasmin, but a 200-fold higher concentration, as compared to plasmin-α₂-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 α₂-antiplasmin, as a result of complex formation with plasmin. A method for determination of plasmin-α₂-antiplasmin complex in plasma has been elaborated using the described radioimmunoassay. About 1.5 mg plasmin-α₂-antiplasmin complex/1 can be detected, which equals the condition when about 1% of the α₂-antiplasmin in plasma is in complex with plasmin. In normal individuals plasmin-α₂-antiplasmin complex could be detected only rarely. However, patients with acute processes, as evidenced by high fibrinogen levels, surgical patients postoperatively or patients with malignancy have often detectable levels.

Key Words:

• conformational changes
• fibrinolysis
• neoantigen
• protease-inhibitor complex