We used high-resolution EM and immunocytochemistry in combination with different specimen preparation techniques to resolve the ultrastructure of the resting platelet cytoskeleton. The periphery of the cytoskeleton, an electron-dense subplasmalemmal region in thin section electron micrographs, is a tightly woven planar sheet composed of a spectrin-rich network whose interstices contain GPIb/IX-...

The conformation of the A1 domain of von Willebrand factor (vWF) is a critical determinant of its interaction with the glycoprotein (GP) Ib/V/IX complex. To better define the regulatory mechanisms of vWF A1 domain binding to the GPIb/V/IX complex, we studied vWF-dependent aggregation properties of a cell line overexpressing the GPIbalpha, GPIbbeta, and GPIX subunits (CHO-GPIbalphabeta/IX cells)...

Glycoproteins (GPs) IIb/IIIa and Ib/IX are principal targets of autoantibodies (autoAbs) in idiopathic thrombocytopenic purpura (ITP). Platelet-associated Abs against GPIIb/IIIa primarily recognize discontinuous or nonlinear epitopes (Fujisawa et al, Blood 81:1284, 1993). This study focused on whether Abs against the extracellular domain of GPIb/IX might react with short linear amino acid (aa) ...

To determine if megakaryocytes are targeted by immune thrombocytopenic purpura (ITP) autoantibodies, as are platelets, we have studied the effects of ITP plasma on in vitro megakaryocytopoiesis. Umbilical cord blood mononuclear cells were incubated in the presence of thrombopoietin and 10% plasma from either ITP patients (n = 53) or healthy donors. The yield of megakaryocytic cells, as determin...

Adhesion of platelets to sites of vascular injury is critical for hemostasis and thrombosis and is dependent on the binding of the vascular adhesive protein von Willebrand factor (vWf) to the glycoprotein (GP) Ib-V-IX complex on the platelet surface. A unique but poorly defined characteristic of this receptor/ligand interaction is its ability to support platelet adhesion under conditions of hig...

We studied the role of von Willebrand Factor (vWF) in platelet thrombus formation in flowing blood by using a perfusion system and mutant forms of vWF lacking either interaction with glycoprotein Ib (GpIb) or with glycoprotein IIb/IIIa (alphaIIb-beta3). These mutants were added to the blood of patients with severe von Willebrand's disease (vWD) or to normal blood reconstituted with a human albu...

We recently reported that after activation of human platelets by thrombin, glycoprotein (GP) Ib-IX complexes are translocated to the surface-connected canalicular system (SCCS) (Blood 76:1503, 1990). As GPIb is a major receptor for von Willebrand factor (vWF) in platelet adhesion, we have now examined the consequences of thrombin activation on the organization of vWF bound to GPIb on the platel...

The binding of plasma von Willebrand factor (VWF) to platelet receptor GpIb under high hydrodynamic shear leads to platelet activation and subsequent shearinduced platelet aggregation (SIPA). We quantitatively examined the aspects of fluid flow that regulate platelet activation by subjecting human blood and isolated platelets to well-defined shear conditions in a cone-plate viscometer. We made ...