Fig. 1

Biogenesis, biomarkers, and cargos of exosomes. A Endocytosis and plasma membrane invagination enable extracellular constituents and cell surface proteins to invade cells. Early endosomes are formed when a plasmalemma buds and fuses with the endoplasmic reticulum, trans Golgi body, and mitochondrial constituents. Then, late endosomes are formed, which undergo a second invagination by cargo modification, resulting in the generation of various ILVs and the development of MVBs. The majority of MVBs will then be transferred to the plasmalemma and dock on the inner face, while others fuse with lysosomes via autophagosomes, causing their contents to be degraded. Finally, MVBs release ILVs to the outside of the cell through exocytosis and become exosomes. Exosomes originating from other cells may also be taken up by the cell in the meantime [28]. B Exosomes include a variety of nucleic acids, amino acids, proteins, and metabolites. Rab GTPases, ESCRT proteins (see text), and other proteins that are often recognized as exosome biomarkers are among the proteins implicated in exosome biogenesis (CD9, CD81, CD63, flotillin, TSG101, ceramide, and Alix). Proteins on the surface of exosomes include tetraspanins, integrins, and immunomodulatory proteins [26]. C Exosomes may also contain intracellular proteins, RNA, DNA, amino acids, and metabolites, among other things [34]. (Note: This figure was created by the authors and there is no confliction of copyright.)