Fig. 1

Biogenesis, release, structure, and uptake of exosomes. In A, exosomes are repressed by small vesicles of different sizes that are formed as the ILV by budding into early endosomes and multivesicular body and are released by fusion of multivesicular body fuse with lysosomes. (a). By endocytosis of membrane segments, the initial endosome arises, containing receptors and transmembrane proteins of the plasma membrane. (b). Instead of lysosomal degradation, the matured late endosome transforms by inward budding of tiny vesicles into a multivesicular body. Furthermore, the exosomal cargo as proteins and miRNA, is selectively loaded into the vesicles. (c). Exosomes are released into the extracellular space by fusion of the multivesicular body with the plasma membrane. (d). Cell-secreted exosomes can travel through biological fluids (e.g. serum, lymph) and be internalized by recipient cells. Exosomes transfer information to the target cells through three main ways: (1) direct fusion with plasma membrane; (2) receptor-ligand interaction; (3) endocytosis by phagocytosis. In B, The membrane of the MVBs bulges inward to form exosomes. During this process, proteins (e.g., receptor, cytoplasmic proteins, tetraspanin), nucleic acids (e.g., DNA, mRNA, miRNA), and lipids (e.g., cholesterol, ceramide) are packed into exosomes in a cell type-dependent manner