Antigenic markers on fragment DD, a unique plasmic derivative of human crosslinked fibrin

Abstract

Abstract Plasmic degradation of crosslinked human fibrin produces unique degradation products, (DD)E complex and fragment DD, in which the DD moiety contains two fragment D molecules joined together by cova-lent bonds. In this study, fragment DD antigenic markers were studied using two different antisera: one against intact (DD)E complex, and the other against fragment DD that has been exposed to 3 M urea at pH 5.5. Antisera were absorbed with fibrinogen and purified fibrinogen degradation products. Direct binding and inhibition of binding of labeled antigens with the antiserum against (DD)E complex showed a 50-fold greater reactivity with fragment DD, as compared with fragment D from fibrinogen or noncrosslinked fibrin. Fibrinogen did not inhibit such binding. In this system, 50% inhibition of binding was achieved with 9 μg/ml of fragment DD. Using the antiserum against fragment DD exposed to acid urea, this antigen was 100-fold and 20-fold more reactive than were acid-urea-treated fragments D prepared from fibrinogen and noncrosslinked fibrin, respectively. Acid-urea-treated fibrinogen was 2000-fold less reactive on a molar basis than was acid-urea-treated fragment DD, and unmodified fibrinogen and fragment D moieties were even less reactive. The sensitivity of this system was greater than that using the antiserum against (DD)E complex, with 50% inhibition achieved using only 300 ng/ml of fragment DD exposed to acid urea. Thus, the difference in antibody reaction with crosslinked and noncrosslinked fragment D moieties demonstrated fragment DD antigenic markers that probably result from unique structural features in this degradation product. However, these crosslink-related markers represented only a small proportion of the total antigenicity of fragment DD, which bears striking similarity to that of other fragment D derivatives.