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

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 covalent 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 50fold 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 ig/ml of fragment DD. Using the antiserum against fragment DD exposed to acid urea, this antigen was 1 00-fold and 20-fold more reactive than were acid-ureatreated 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.