A monoclonal antibody recognizes a von Willebrand factor domain within the amino-terminal portion of the subunit that modulates the function of the glycoprotein IB- and IIB/IIIA-binding domains.

Abstract

We developed a monoclonal antibody, 1C1E7, against vWf that increases ristocetin-induced platelet aggregation in a dose-dependent manner and lowers the threshold concentration of ristocetin needed to obtain a full aggregatory response. The platelet aggregatory effect of asialo vWf (ASvWf) also is enhanced by 1CIE7, in the presence or absence of glycoprotein (GP) Ilb/IlIa receptor antagonism. In the presence of ristocetin, both intact 1ClE7 and its Fab fragments enhance specific binding of '25I-vWf to platelets. With 1ClE7, the intermediate and higher molecular weight multimers of vWf are preferentially bound to both GP lb and GP IIb/IIIa. Thrombin-induced 125I-vWf binding to GP IIb/Illa also is increased by 1ClE7. Maximal binding of 1C1E7 to vWf corresponds to 0.97 mol/mol vWf monomer with a Kd of 4.7 x 10-10 M. 1ClE7 reacts with a 34 /36-kD tryptic fragment (III-T4) and a 34-kD plasmic fragment (P34), which localizes the epitope between amino acid residues 1 and 272; this was confirmed by NH2-terminal amino acid sequencing. Finally, platelet aggregation by ASvWf was associated with a sharp rise in intracellular Ca2+ only in the presence of 1C1E7. An antibody-mediated conformational change of vWf may result in an improved presentation of the GP Ib-and GP IIb/ IIIa-binding domains of mainly the larger multimers; the increased density of vWf on the platelet surface leads to platelet activation. The antibody may thus recognize a domain of relevance for vWf physiology. (J. Clin. Invest. 1993. 91:273-282.)

Shielding of the A1 Domain by the D′D3 Domains of von Willebrand Factor Modulates Its Interaction with Platelet Glycoprotein Ib-IX-V

“…Previous studies demonstrated that 1C1E7 interacted with a tryptic fragment comprising the aa 764 -1035 sequence in VWF, which is located in the DЈD3 region (15). The location of the epitope was further corroborated by the fact that 1C1E7 failed to interact with ⌬DЈD3 but recognized the isolated DЈD3 region (data not shown).…”

“…moAb 82D6A3 binds to the VWF A3 domain and inhibits VWF binding to collagen types I, III, and IV (17), and moAb 1C1E7 recognizes the N-terminal part of VWF (aa 764 -1035) (15). moAbs 724, 701, and 418 were kind gifts of Dr. J. P. Girma (INSERM U143, le Kremlin-Bicê-tre, Paris, France).…”

“…We have previously described a monoclonal antibody (moAb), 1C1E7, directed against the aa 764 -1035 region in the N-terminal DЈD3 domains of VWF (15). Although this moAb interacts with a region distinct from the VWF A1 domain, it induces von Willebrand diseasetype 2B-like alterations (16).…”

Identification of a Small Molecule That Modulates Platelet Glycoprotein Ib-von Willebrand Factor Interaction

“…Next, ristocetin (abp, New York) was added to a final concentration of 1 mg/ml, and the mixture was incubated for another 1.5 h at 37°C to induce VWF-GPIb␣ binding. 0.5 g/ml of the inhibitory anti-GPIb␣ mAb 6B4 (4 -6) and 25 g/ml of the VWF-activating mAb 1C1E7 (46,47) were used as a control. The mAb 1C1E7 renders the VWF more accessible for GPIb␣ binding by disrupting the interaction of the VWF DЈD3 that shields the VWF-A1 domain.…”

Acquired Bernard-Soulier Syndrome: A Case with Necrotizing Vasculitis and Thrombosis

“…Blood was collected into trisodium citrate, pH 7.5 (0.11 M, 0.1 vol) and immediately centrifuged at 180 g for 10 min to obtain platelet-rich plasma (PRP). Gel-filtered platelets were prepared as was described previously [11].…”