A rapid latex immunoassay for the detection of plasmin-alpha 2-plasmin inhibitor complex. Utilization of two monoclonal antibodies differentially recognizing respective components of the complex.

Among six monoclonal antibodies raised against the human plasmin-alpha 2-plasmin inhibitor complex (PPI), three antibodies were found to recognize the plasmin part (group 1) and another three the alpha 2-plasmin inhibitor (alpha 2-PI) part (group 2) of the complex. One of the group-1 monoclonal antibodies, designated JIPPI-3, specifically reacted with a segment of plasmin containing kringles 2 and 3. Although all three group 2 antibodies reacted with both alpha 2-PI and PPI on immunoblotting and ELISA, one of them, JIPPI-50, was unable to react with alpha 2-PI, when the antibody had been covalently conjugated to Sepharose 4B gels and tested for reactivity against the antigens in solution. The results indicated that the epitope for this antibody had been buried in nascent alpha 2-PI, but had been exposed by complex formation with plasmin or by possible conformational changes induced in the alpha 2-PI molecule on insolubilization to nitrocellulose membranes or immunoplates. By utilizing a set of JIPPI-3 and JIPPI-50, individually coated onto latex beads, PPI could be measured in plasma in the range of 0.8-100 micrograms/ml without interference by coexisting plasminogen (120-200 micrograms/ml) or alpha 2-PI (70 micrograms/ml). This measurable range seems to cover the level of PPI clinically observed under hyperfibrinolytic states.