Interaction of HEK 293 cells expressing either normal αIIbβ3 or the constitutively active αIIbβ3 mutant αIIb(FF)β3 with fibrinogen, D98, and D-dimer. (A) HEK 293 cells expressing normal αIIbβ3 (normal αIIbβ3) adhered to fibrinogen, but not D98 or D-dimer, whereas HEK 293 cells expressing the constitutively active mutant αIIb(FF)β3 adhered well to D98 and D-dimer in addition to fibrinogen. (B) Inhibition of adhesion of HEK cells expressing αIIbFFβ3 to D-dimer by the polyclonal anti–D-dimer antibody IgG. (C) The Asp119Ala mutation, which disrupts the β3 MIDAS region, inhibited adhesion of HEK cells expressing αIIbFFβ3 to D98 and D-dimer. (D) The small-molecule αIIbβ3 antagonists eptifibatide (100 μM) and tirofiban (10 μM), which bind to the RGD binding pocket, inhibited the adhesion of HEK cells expressing αIIbFFβ3 to D-dimer (P < .001 for all vs control; n = 4), as did the ligand-blocking anti-αIIbβ3 mAbs 10E5 and 7E3 (20 μg/mL for both; P < .001 for both; n = 4), but not the mAb 7E9 directed at the C-terminal region of the fibrinogen γ-chain (P = .25; n = 4).