Development and clinical application of a new ELISA assay to determine plasmin–α2-antiplasmin complexes in plasma

Plasmin–α₂-antiplasmin complexes (PAP) are considered good markers of fibrinolytic activation in vivo . The presence of neoantigens in these complexes offers the possibility to develop specific immunoassays to determine PAP levels. We have developed a sensitive PAP purification method in vitro by adding urokinase to fresh plasma followed by affinity chromatography to lysine-sepharose and elution with ε-aminocaproic acid. This material, characterized by SDS-PAGE and Western blotting, was used to raise monoclonal antibodies (MoAbs). We describe a new enzyme-linked immunosorbent assay (ELISA) to quantify PAP complexes in plasma. The assay follows the sandwich principle and is based on two MoAbs, CPL12 and CPL15, that bind to the modified α₂-antiplasmin moiety and the plasmin moiety of the complex respectively. The calibration curve was constructed with definite concentrations of purified PAP. The lower limit of the assay is 75 ng/ml and the variation coefficients are 3.5% (intra-assay) and 10.6% (interassay). A mean value of 573.5 ± 131.4 ng/ml was obtained from PAP concentration in a healthy population ( n  = 30). Significantly higher PAP levels were observed under diverse clinical conditions in which fibrinolysis is activated: clinical sepsis, acute myocardial infarction (AMI), malignancy, diabetes, pregnancy, elderly people and thrombolytic therapy. From our results we conclude that this ELISA is suitable to measure in vivo plasma PAP levels.