Exosome morphology and the molecular content. In A, transmission electron microscopy (TEM) of tumor-derived exosomes isolated from a tumor cell supernatant, pelleted by ultracentrifugation, embedded in Epon, sectioned and viewed by TEM. Note different sizes of membranous vesicles (courtesy of Dr. Simon Watkins, University of Pittsburgh). In B, the cartoon of an exosome illustrating the presence of a broad variety of molecules on its surface (some of the most common are indicated) and in the vesicle lumen.