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We have developed a two-step enzyme immunoassay (EIA) that allows the quantitation of degradation products derived from fibrinogen (FbgDP) and that does not detect degradation products derived from cross-linked (XDP) or noncrosslinked fibrin (fdp). The EIA is based on two monoclonal antibodies (FDP-14 and Y-18), developed in our institute. FDP-14 is used as catching antibody. It complexes exclusively with degradation products, irrespective whether these are derived from fibrinogen or from fibrin. It does not complex with intact fibrinogen or fibrin. Y-18 is reactive with fibrinogen and fibrinopeptide A-comprising fibrinogen fragments. It is used, conjugated with horse-radish peroxidase, as tagging antibody. The FbgDP-EIA is highly specific, accurate and sensitive. The coefficient of variation is between 3 and 8%; the lower detection limit is less than 0.025 micrograms/ml. The assay has been applied to plasma from patients with suspected disseminated intravascular coagulation (DIC), to plasma from patients undergoing streptokinase (SK) therapy for acute myocardial infarction and to plasma from newborn babies. DIC patients had no or very low levels of FbgDP, but high levels of other degradation products, SK-treated patients showed high levels of degradation products two hours after termination of the SK infusion. A considerable fraction of these degradation products was shown to be FbgDP. Plasma from newborn babies contained elevated levels of FbgDP associated with prolonged prothrombin times.

Spleen cells of BALB/c mice, immunized with fragments Y of normal human fibrinogen, were fused with P3 X 63 Ag 8653 myeloma cells. A clone was found which produces monoclonal antibodies (Mab-Y18) of the IgM kappa type. Mab-Y18 is immunoreactive with normal human fibrinogen, and its fragments X, Y, N-terminal disulphide knot, A alpha-chain, and A alpha stretch 1-51. The immunoreactivity with these same fragments disappears upon treatment with thrombin or arvin. This strongly suggests that fibrinopeptide A is an essential component of the Mab-Y18 epitope. This is supported by the finding that Mab-Y18 prolongs the thrombin and arvin clotting times of human fibrinogen by inhibition of the fibrinopeptide A release. More detailed information about the nature of the Mab-Y18 epitope was obtained from studies with genetic variants of human fibrinogen (especially fibrinogen Metz) and with fibrinogens from other mammalian species. These studies show that amino acid residue A alpha 16 (arginine) of fibrinopeptide A is essential for the Mab-Y18 epitope. Mab-Y18 does not react with free fibrinopeptide A.

Balb/c mice were immunized with a mixture of fibrin degradation products (XDPs) prepared by complete lysis of a human blood clot by tissue-type plasminogen activator and purified by immunoaffinity chromatography. Spleen cells of the mice were fused with P3 X 63 Ag 8653 myeloma cells. A clone (FDP 14) was selected that produces monoclonal antibodies (MoAbs) of the IgG1 kappa type that react with a neoantigenic determinant exposed in these XDPs, but not in intact fibrinogen or in fibrin monomers. Furthermore, the MoAb is reactive with some pure, individual degradation products of fibrinogen (fragments X, Y, E, and the N-terminal disulphide knot) and with the fibrinogen B beta-chain but not with A alpha- and gamma-chains or with fragments D, FCB-2 and FCB-3. Comparison of the known primary structures of these fibrinogen fragments indicates that the stretch B beta 54-118 comprises at least an important part of the epitope recognized by FDP-14. Apparently, this stretch contributes importantly to a neoantigenic determinant that is not functional in intact fibrinogen and fibrin monomer and that can be made functional by reduction of fibrinogen, or by digestion with plasmin or CNBr.

Balb/c mice were immunized with human plasmin-generated fibrinogen degradation product Y. Spleen cells were fused with P3X63-Ag8.653 myeloma cells. A clone (Y22) was found that produces monoclonal antibodies (MoAbs) with a strong reactivity with human fibrin and only a weak reactivity with fibrinogen in an enzyme immunoassay (EIA). Y22 also reacts with fibrin of rabbits, rats, sheep, and dogs. The antibodies are of the IgG1 kappa-type and appear to be directed against a conformation-dependent epitope in the D-domain of fibrin. Experiments with 99mTc-labeled Y22 in vitro show that Y22 binds rapidly to forming clots. 99mTc-Y22 also binds to preformed plasma clots in a plasma milieu, even in the presence of high concentrations of heparin. Clot localization experiments in rabbits and rats confirm the high fibrin specificity and the potential of 99mTc-Y22 for thrombus imaging in vivo.

We have developed a sandwich-type enzyme immunoassay (EIA) for the quantitation of fibrin degradation products (FbDP) in plasma with a time-to-result of only 45 minutes. The assay is based on the combination of the specificities of two monoclonal antibodies (FDP-14 and DD-13), developed in our institute. FDP-14, the capture antibody, binds both fibrinogen degradation products (FbgDP) and FbDP, but does not react with the parent fibrin(ogen) molecules. It has its epitope in the E-domain of the fibrinogen molecule on the B beta-chain between amino acids 54-118. Antibody DD-13 was raised using D-dimer as antigen and is used as a tagging antibody, conjugated with horse-radish peroxidase. A strong positive reaction is obtained with a whole blood clot lysate (lysis induced by tissue-type plasminogen activator) which is used as a standard. The EIA does virtually not detect FbgDP i.e. purified fragments X, Y, or FbgDP generated in vitro in plasma by streptokinase treatment. This indicates that the assay is specific for fibrin degradation products. We have successfully applied this assay to the plasma of patients with a variety of diseased states. In combination with the assay previously developed by us for FbgDP and for the total amount of FbgDP + FbDP (TDP) in plasma, we are now able to study the composition of TDP in patients plasma in terms of FbgDP and FbDP.

A specific glucagon antiserum was generated in rabbits using a derivatisation of the methionine residue in glucagon. A sensitive and specific assay for glucagon has been developed. Interference with the assay system by plasma factors was abolished by both extraction of plasma samples and the production of glucagon-free plasma for each individual.