title: Induction of GPIb/IX-vWF receptor-ligand translocation on surface-activated platelets.
abstract: Multimers of von Willebrand factor (vWF) readily bind to glycoprotein (GP) Ib/IX receptors on spread human platelets and cover the cell from edge to edge. Addition of anti-vWF antibody to spread platelets covered with vWF caused the multimers to move from peripheral margins into caps over platelet centers. Despite almost complete centralization of receptor-ligand complexes, a significant number of GPIb/IX receptors capable of binding multimers remained available on the peripheral zone. Fixation followed by a second incubation with vWF, anti-vWF, and staph protein A coupled to 5-nm gold particles (PAG5) revealed multimers extending from the centrally concentrated cap of vWF to cell margins. If spread platelets with central caps of vWF were exposed a second time to multimers and anti-vWF antibody before fixation and stained with PAG5 after, the residual GPIb/IX receptors and second wave of vWF formed a ring around the cap, leaving a clear margin. If after fixation and staining with PAG5 the grids with caps and rings of vWF were washed, exposed a third time to vWF, refixed, and then incubated with anti-vWF and PAG10, the clear margin was covered with multimers of vWF forming a second ring around the first circle of receptor-ligand complexes. Thin sections of spread platelets with central caps of GPIb/IX-vWF complexes revealed only rare examples of uptake by the open canalicular system. The interaction of GPIb/IX with vWF multimers observed in the present study suggests a mechanism by which platelets under high shear forces may adhere and attach firmly to a denuded vascular surface.
authors.affiliation: Department of Laboratory Medicine and Pathology, University of Minnesota Medical School, Minneapolis 55455, USA.
authors.forename: J G
authors.initials: JG
authors.lastname: White
authors.forename: M D
authors.initials: MD
authors.lastname: Krumwiede
authors.forename: D
authors.initials: D
authors.lastname: Cocking-Johnson
authors.forename: G
authors.initials: G
authors.lastname: Escolar
mesh_terms: D000906:Antibodies / Q000276:immunology; D000911:Antibodies, Monoclonal / Q000276:immunology; D001692:Biological Transport; D001792:Blood Platelets / Q000378:metabolism*; D055598:Chemical Phenomena; D002621:Chemistry; D003584:Cytological Techniques; D005404:Fixatives; D006801:Humans; D008024:Ligands; D015539:Platelet Activation; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000276:immunology / Q000378:metabolism*
chemical_list: D000906:Antibodies; D000911:Antibodies, Monoclonal; D005404:Fixatives; D008024:Ligands; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; C032193:glycoprotein receptor GPIb-IX; C028254:von Willebrand factor receptor