Does Fibrin Fragment D-Dimer Cross-Link With Fibrin Monomer?

When 2 to 4 ng of radioiodinated human D-dimer (D-D) and 0.2 mg of carrier rabbit D-D in two ml of buffer were added to a .7x10 cm column containing 4 ml of agarose-linked rabbit, or human fibrin monomer, D-D was tightly bound. After a neutral buffer wash D-D was quantitatively eluted (97 to 99% recovery) with 6M urea (pH 8.6). Comparable recovery of unlabeled human D-D, 500 to 8000 ng, was achieved. Human D-D concentration was measured by radioimmunoassay with rabbit anti-human D-D serum. When labeled or unlabeled D-D was mixed with 2ml of serum or when serum from patients with high D-D levels was chromatographed, 40 to 70% of D-D was retained and could not be eluted even by washing the column with alkaline urea for 24 to 48 hours. Irreversible binding of D-D could not be prevented by adding DFP or Tween 20 or by pre-heating the carrier serum to 60°, but binding was completely prevented by 5 mM EDTA in the serum and eluting solutions. Let’s than 1% of labeled D-D remained on the affinity agarose. We have previously suggested that only one of two reciprocal gamma chain cross-linking sites is used when fibrinogen cross-linking takes place (S. Afr. J. Sci., 74:202, 1978). Activated factor XIII could utilize the spare site to form epsilon (gamma glutamyl)lysine bonds between insolubilized fibrin monomer and D-D.