Demonstration of β-TG and CD63 in cultured megakaryocytes. Immunogold double-labeling as indicated on the figure. (A) Specific labeling of β-TG is demonstrated in the Golgi complex (g), α-granules, and MVB II (arrows). Colocalization with CD63 (arrowheads) is restricted to the MVBs. (B) Detailed demonstration of colocalization of β-TG with CD63 in a MVB II. Note that the labeling of CD63 is associated with membranes of the internal vesicles and that of β-TG with the matrix. Bars A, 500 nm; B, 200 nm.