D-dimer, D98, an anti D-dimer pAb, and mAb 7E3 inhibit clot retraction, but mAb 10E5 does not. (A) Clot retraction in the absence and presence of D-dimer and D98. Washed platelets (3 × 10⁸/mL) were incubated for 20 minutes with 200 μg/mL BSA, D-dimer, or D98 and then added to a glass cuvette containing thrombin (0.2 U/mL) and 1 mM CaCl₂. (B) Anti–D-dimer pAb inhibited clot retraction. Washed platelets (3 × 10⁸/mL) were incubated for 10 minutes with the indicated concentration of anti–D-dimer pAb and 100 µg/mL human fibrinogen and then added to a glass cuvette containing 0.2 U/mL thrombin and 1 mM CaCl_2. (C) Effect of monoclonal antibodies 7E3 and 10E5 on clot retraction. Clot retraction was performed as indicated in panel A, either in the absence (control; C) or presence of 50 µg/mL of each of the antibodies. The clot area is expressed in square pixels. (D) Immunoblot of the fibrinogen γ-chain at time 0 and 20 minutes of clot retraction. Samples from a control clot retraction experiment were solubilized in sodium dodecyl sulfate and immunoblotted with an antibody to the fibrinogen γ-chain. At 20 minutes, nearly all of the γ-chain had transitioned into γ-γ dimers.