Immunogold labeling of VWF on cultured cells. Megakaryocytes at day 12 from cultures of CD34⁺ cells isolated from the peripheral blood of patient 1 were fixed, and frozen thin sections were stained sequentially using a polyclonal anti-VWF antibody and a secondary antibody to rabbit IgG adsorbed onto 10-nm gold beads. Transmission electron microscopy revealed that VWF was present on the cell surface (arrowheads, panel A) as well as in intracellular canals (arrows, panels A-C) and in well-developed α-granules (D-E). Multivesicular bodies (MVB) are seen in panel E. Scale bars equal 500 nm.