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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1995;15:642-654.)
© 1995 American Heart Association, Inc.

Articles

Induction of GPIb/IX-vWF Receptor-Ligand Translocation on Surface-Activated Platelets

James G. White; Marlys D. Krumwiede; Debra Cocking-Johnson; Gines Escolar

From the Departments of Laboratory Medicine and Pathology, Pediatrics, University of Minnesota Medical School, Minneapolis, and the Servicio de Hemoterapia y Hemostasia (G.E.), Hospital Clinico y Provincial, Barcelona, Spain.

Correspondence to James G. White, MD, Regents' Professor, Departments of Laboratory Medicine and Pathology, Pediatrics, University of Minnesota Medical School, UMHC Box 490, 420 Delaware St SE, Minneapolis, MN 55455.

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.

Key Words: surface activation • spread platelets • von Willebrand factor • anti–von Willebrand factor • protein A gold

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