OBJECTIVE Thrombin containing the mutations Trp215Ala and Glu217Ala (WE) selectively activates protein C and has potent antithrombotic effects in primates. The aim of this study was to delineate the molecular mechanism of direct WE-platelet interactions under static and shear conditions. METHODS AND RESULTS Purified platelets under static conditions bound and spread on immobilized wild-type b...

The functional activity of von Willebrand factor (VWF) is most frequently measured by using the ristocetin cofactor assay (VWF:RCo). However, the method's drawbacks include unsatisfactory precision, sensitivity and availability of automated system applications. We have developed an alternative assay (INNOVANCE VWF Ac) that is based on the binding of VWF to recombinant glycoprotein Ib (GPIb). Tw...

Glycoprotein Ib-IX-V (GPIb-IX-V) mediates platelet tethering to von Willebrand factor (VWF), recruiting platelets into the thrombus, and activates integrin alphaIIbbeta3 through a pathway that is dependent on Src kinases. In addition, recent reports indicate that activation of alphaIIbbeta3 by VWF is dependent on protein kinase G (PKG) and mitogen-activated protein (MAP) kinases. The present st...

An aberrant platelet immunorelated glycoprotein Ib (GPIb) receptor expressed by human tumor cells appears to participate in primary adhesive interactions required for the metastatic process. Hence, we questioned whether plasma von Willebrand's factor (vWf), its adhesive ligand, manifested comparable anomalies in patients with disseminated tumors. Plasma specimens from patients with disseminated...

Bostjan Kobe THE UNIVERSITY OF QUEENSLAND Understanding the mechanism of platelet activation requires the knowledge of the structural organization of the glycoprotein (GP) Ib-IX-V receptor. In this issue of Blood, an innovative structural approach was used to shed light on the interaction between GPIb and GPIX subunits.1 The GPIb-IX-V complex serves as the platelet receptor that mediates bindin...

Recent studies have shown that antibodies characteristic of quinine- and quinidine-induced thrombocytopenia sometimes recognize the platelet membrane glycoprotein (GP) complex IIb/IIIa in addition to their well known target, GPIb/IX. We have investigated the frequency with which drug-induced antibodies bind to GPIIb/IIIa and the nature of their target epitopes. In studies of sera from 13 patien...

Platelets subjected to elevated levels of fluid shear stress in the absence of exogenous agonists will aggregate. Shear stress-induced aggregation requires von Willebrand factor (vWF) multimers, extracellular calcium (Ca2+), adenosine diphosphate (ADP), and platelet membrane glycoprotein (GP)Ib and GPIIb-IIIa. The sequence of interaction of vWF multimers with platelet surface receptors and the ...

We found that the interaction of platelets with immobilized von Willebrand factor (VWF) under flow induces distinct elevations of cytosolic Ca concentration ([Ca ]i) that are associated with sequential stages of integrin IIb 3 activation. Fluid-dynamic conditions that are compatible with the existence of tensile stress on the bonds between glycoprotein Ib (GPIb ) and the VWF A1 domain led to Ca...

The Wiskott-Aldrich syndrome (WAS) is an inherited disease involving defects of platelets (small size, severe thrombocytopenia due to accelerated destruction) and T lymphocytes (progressive immunodeficiency, lymphopenia). The best-characterized molecular defect is the deficiency and, in some cases, abnormal forms of the T-lymphocyte surface mucin molecule CD43; deficiency of the platelet surfac...