Double-staining for c7E3 and clathrin on platelet sections after the incubation of platelets with abciximab for 5 minutes in vitro. Clathrin was detected with a mouse MoAb, in turn localized with goat anti-mouse IgG adsorbed to 10 nm gold particles (heavy arrows). Abciximab was detected using rabbit antibody itself detected using anti-rabbit IgG adsorbed onto 5 nm gold particles (thin arrows). In (A) a vesicle in close proximity to a granule contains both abciximab and clathrin, in (B and C) clathrin and abciximab are both associated with the membrane of -granules, and in (D) a small vesicle containing clathrin and abciximab appears to be fusing with an -granule. Bars = 0.2 μm.