Eccentric Localization of von Willebrand Factor in an Internal Structure of Platelet α-Granule Resembling That of Weibel-Palade Bodies

Abstract

AbstractImmunogold staining was used to study the ultrastructural distribution of von Willebrand factor (vWF) in unstimulated platelets. vWF was detected in the α-granules with a specific eccentric distribution pattern opposite the nucleoids. Similar findings were obtained with a polyclonal antibody or a pool of monoclonal antibodies to human vWF. This labeling coincided with the presence of tubular structures located at the periphery of the α-granules. These structures were better visualized on platelets treated for standard electron microscopy: they formed a group of one to four tubules ranging from 200 Å to 250 Å in diameter. They closely resembled the internal tubular structures found in Weibel-Palade bodies, which are the storage organelles of vWF in endothelial cells.