Immunocytochemical localization of factor VIII-related antigen in the human umbilical vein

The immunocytochemical localization of factor VIII-related antigen in the human umbilical vein was investigated with the light microscopic immunoperoxidase and immunoelectron microscopical protein A-gold techniques. The light microscopic observation showed that peroxidase reactions were found exclusively in the endothelia of the vessel. By the protein A-gold method, immunoreactive gold particles were located in endothelial specific granules (Weibel-Palade bodies). These data suggest that endothelial specific granules are storage sites of factor VIII-related antigen.