Ultrastructural identification of platelet surface glycoproteins and particle endocytosis with gold-labeled reagents

Blood platet surface labeling was obtained by the use of the lectins concavalin A and wheat germ agglutinin. Colloidal gold particles coated with horseradish peroxidase and ovomucoid respectively were used as markers. Also erythrocytes and leukocytes were labeled. Using monoclonal antibodies against the platelet surface glycoproteins Ib and IIb-IIIa specific labeling of the platelets was obtained, whereas the red cells and the leukocytes were entirely free of labeling. With glutaraldehyde fixed platelets no gold particle uptake was observed. With unfixed normal platelets, however, surface membrane-associated particles were sometimes observed within the surface connecting canalicular system, and occasionally in small vesicles. In unfixed platelets from a patient with thrombocytopathia, possible platelet endocytosis of the membrane bound particles was observed with particles assumed to be transported via vesicles to granules probably representing lysosomal structures.