QUANTITATIVE IMMUNOLOGICAL DETERMINATION OF HUMAN FIBRIN-DEGRADATION AND FIBRINOGEN-DEGRADATION PRODUCTS (FDP) IN PLASMA WITH AN ANTIBODY AGAINST A SYNTHETIC PEPTIDE

A new method has been developed for the quantitative determination of fibrin - and fibrinogen degradation products (FDP) in plasma. An epitope on the gamma-chain of fibrin(ogen) hidden in intact molecules is exposed in fragments E after cleavage by plasmin. A synthetic peptide of this new carboxy terminus has been used for immunization of rabbits. Antibodies isolated by immunoabsorption against a partial sequence of this peptide did not react with intact fibrinogen or fibrin, but recognized equally well all fragments E liberated from fibrinogen (AABB-E(3)), cross-linked (E(1) and E(2)) and non cross-linked fibrin (E(3)). In a sandwich-type enzyme immunoassay, the antibodies obtained were used for coating of microtitration plates, and polyclonal anti-E antibodies coupled to peroxidase for detection of bound FDP. The validity of the assay was investigated by incubation of normal and alpha(2)-antiplasmin depleted plasma with plasmin. Only in the alpha(2)-antiplasmin depleted plasma a significant and steady increase of FDP levels was detectable, reflecting in vitro generation of FDP. Since fragments E are only liberated by action of plasmin, the assay via quantification of FDP reflects free plasmin activity in vivo.