Monoclonal Antibody to Fibrin D-Dimer (DD-3B6) Recognizes an Epitope on the γ-Chain of Fragment D

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Abstract
Laboratory determination of fibrinolysis has been facilitated by diagnostic tests that use monoclonal antibody DD-3B6 to measure fibrin D-dimer levels in plasma. When DD-3B6 is reacted with soluble fibrin fragments, it is specific for fragment D-dimer. The authors have used immunoblot analysis of DD-3B6 binding to purified fragment D and fragment D-dimer to localize the binding site of the antibody. Although DD-3B6 recognizes only fragment D-dimer in solution, it binds to both immobilized fragment D-dimer and fragment D in immunoblots. When immunoblots were performed using protein which was electrophoresed under reducing conditions, DD-3B6 bound to the γ-chain of fragments D1, D2, and D3. Therefore, the epitope recognized by DD-3B6 resides between amino acids 86 and 302 in the γ-chain of fragment D. This epitope is masked in soluble non-cross-linked or nondegraded fibrin, but becomes expressed after cross-linked fibrin has been cleaved by plasmin.