Abstract
Beta-thromboglobulin (beta TG) and platelet factor 4 (PF4) have been localised in megakaryocytes and platelets using immunofluorescence and immunoperoxidase techniques. These studies support the concept of synthesis of the proteins by parent megakaryocytes. By immunoelectron microscopy both proteins have been visualised in the alpha granule of the platelet and megakaryocyte, supporting functional studies of the cytoplasmic localisation of these proteins. The light microscopic techniques may allow elucidation of the distribution and role of the megakaryocyte in the pulmonary circulation and, on a practical level, permit its identification and distinction from other multinucleate cells in extramedullary tissue.