Electron micrographs of vesicles shed from CX-1 cells. Large arrowheads point to gold particles in association with Fas antigen on plasma membrane-derived vesicles. In (A), a few gold particles (small arrowheads) not associated with vesicles can be seen and apparently represent nonspecific background. Both micrographs are at 92,000× magnification. Scale bar = 0.2 μm.