Platelet membrane glycoproteins Ib (GPIb) and IIb IIIa ( GPIIb IIIa) bind soluble von Willebrand factor (vWf) after stimulation with ristocetin (GPlb) or with thrombin or ADP ( GPIIb IIIa). In fluid-phase, vWf does not bind to these platelet receptors without stimulation. In contrast, platelets adhere to solid-phase vWf without stimulation by ristocetin, adenosine diphosphate (ADP), or thrombin, and adhesion increases after stimulation by these agonists. The effect of monoclonal antibodies specific for GPIb (6D1) and GPIIb IIIa (10E5 and HP1-1D) on platelet adhesion to solid-phase vWF was studied. Adhesion of radiolabeled, washed platelets (with washed red blood cells) aspirated at a constant wall shear rate of 1000 sec-1 through glass capillary tubes coated with purified human vWf was quantified. Unstimulated platelet adhesion was decreased 80% to 90% by blocking either the GPIb site or the GPIIb IIIa site with 6D1 or 10E5, respectively, or with 6D1 and 10E5 together. Adhesion was not reduced significantly by HP1-1D ( anti-GPIIb IIIa). After stimulation with ADP or thrombin, the platelet adhesion was reduced by prior incubation with saturating concentrations of either 6D1 (61% reduction) or 10E5 (80% reduction), as well as with both 6D1 and 10E5 (80% reduction). After stimulation with ristocetin, the adhesion was reduced with either 6D1 (90% reduction) or 10E5 (90% reduction) or both 6D1 and 10E5 (90% reduction). Prior incubation with HP1-1D had minimal effect on platelet adhesion to vWF after stimulation with thrombin, ADP, or ristocetin. Monoclonal antibody HP1-1D (10 to 25 μg/ml) abolished iodine 125-labeled fibrinogen binding to washed platelets (ADP- or thrombin-stimulated) but did not affect 125I-labeled vWf binding to washed, thrombin-stimulated platelets. These data demonstrate that adhesion of stimulated or unstimulated platelets to solid-phase vWf is dependent on both GPIb and GPIIb IIIa. In addition, the data indicate that the binding of vWf and fibrinogen to the GPIIb IIIa site may involve more than one binding site on the GPIIb IIIa molecule.
|Original language||English (US)|
|Number of pages||9|
|Journal||The Journal of Laboratory and Clinical Medicine|
|State||Published - Aug 1994|
ASJC Scopus subject areas
- Pathology and Forensic Medicine