Illustration depicting a cross-section of an exosome. Exosomes are tiny extracellular vesicles that measure roughly 30-150 nanometres in diameter. These vesicles are surrounded by a lipid bilayer and contain a complex cargo of materials, such as membrane-bound proteins like MHC-II, PD-L1, EGFR, integrins, and tetraspanins, as well as mRNA (messenger ribonucleic acid) and signalling proteins like chaperones. Exosomes serve a number of important functions in the body, including waste management and intercellular communication. They have many potential uses, including as biomarkers for diseases and as vehicles for drug delivery. For an unlabelled version of this image see F038/6908.