Multivesicular bodies and α-granules in human platelets. Modified pick up approach applied to thin frozen sections as described in Materials and Methods. (A and B) Methyl cellulose sucrose pick up after immuno-gold labeling with a nonspecific control antibody and protein-A gold. (C and D) “direct-view” method. (E and F) Immunolabeling as indicated on the figure. The arrow in (B) indicates an α-granule containing internal vesicles at the periphery. Inset: Higher magnification of an α-granule with eccentrically located internal vesicles. (D) Arrowheads indicate peripheral intragranular vesicles. (E) Immunolabeling of vWF using 10 nm protein-A gold. Gold labeling is located at the eccentric rims of the α-granules. Arrowheads indicate two internal vesicles ≈ 40 nm in diameter. (F) Demonstration of CD63 in platelet α-granules using 5 nm protein-A gold. Arrowheads indicate CD63 associated with internal vesicles, which are often located at extended tips of the α-granules. MVB, multivesicular body, α, α-granules. Bars, 100 nm.