Immunological Relationship Between the Fast-Acting Plasminogen Activator Inhibitors from Plasma, Blood Platelets and Endothelial Cells Demonstrated with a Monoclonal Antibody Against an Inhibitor from Placenta

Abstract

Two plasminogen activator inhibitors (I and II) were demonstrated in human placenta. The complex between inhibitor I and tissue-type plasminogen activator was purified by immunoadsorption to solid-phase anti-activator antibodies. The purified complex (Mr 95.000) was used for immunization of mice and subsequent production of monoclonal antibodies. One antibody (F37), which reacted with both free and complex-bound inhibitor I, was used for further study by a method involving binding of the antibody to protein A-Sepharose, immunoadsorption of antigen and analysis of the resulting supernatant by SDS-polyacrylamide gel electrophoresis and enzymography. The analysis showed that F37 reacted with the fast-acting plasminogen activator inhibitors recently demonstrated in plasma, blood platelets and endothelial cells, indicating that these inhibitors and inhibitor I share a common epitope. Inhibitor II did not react with F37. Inhibitor II is identical to the placenta inhibitor previously described by others. It reacted selectively with polyclonal antibodies against that inhibitor.