Anti-DD ELISA System Role of Soluble Crosslinked Fibrin Polymers

After addition of a low concentration of thrombin to normal plasma, a progressive and significant increase in crosslinked fibrin polymers was found by sodium dodecyl sulfate agarose gel electrophoresis, reaching 27% of total fibrinogen and fibrin before gel formation. As measured by enzyme-linked immunosorbent assay with a monoclonal antibody specific for an epitope near the yy crosslink site, increased immunoreactivity of plasma did not occur after adding thrombin despite formation of crosslinked fibrin polymers, which indicates that the antibody does not recognize the epitope in the polymers. Addition of tissue-type plasminogen activator (t-PA) to plasma resulted in a more rapid degradation of fibrin polymers than of fibrinogen, indicating that the fibrin specificity of t-PA is retained with soluble fibrin. Coincident with degradation of plasma crosslinked fibrin polymers, plasma DD immunoreactivity increased 70-fold from 50.3±4.5 (mean±SD) to 3,560±1,235 ng/ml. The presence of increased crosslinked fibrin polymers produced by adding thrombin to plasma significantly increased maximum immunoreactivity after t-PA-induced degradation to 18,500±11,780 ng/ ml. The increase in DD immunoreactivity was dependent on t-PA concentration; no elevation occurred below 0.01 ug/ml, and maximal increases occurred above 100 ,ug/ml. Analysis of gel electrophoretic patterns of thrombin and t-PA-treated plasma samples suggests that the DD reactivity of t-PA-treated plasma is mainly due to degradation of soluble crosslinked fibrin polymers. Our findings indicate that plasmic degradation of soluble fibrin polymers in plasma may be an important source of fragment DD during thrombolytic therapy. (Circulation 1989;79: 666-673)