ECCENTRIC LOCALIZATION OF VONWILLEBRAND-FACTOR IN AN INTERNAL STRUCTURE OF PLATELET ALPHA-GRANULE RESEMBLING THAT OF WEIBEL-PALADE BODIES

Abstract

Immunogold staining was used to study the ultrastructural distribution of von Willebrand factor (vWF) in unstimulated platelets. vWF was detected in the .alpha.-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 .alpha.-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 .ANG. to 250 .ANG. in diameter. They closely resembled the internal tubular structures found in Weibel-Palade bodies, which are the storage organelles of vWF in endothelial cells.