Discrimination between exosomes and HIV-1: purification of both vesicles from cell-free supernatants.

Although enveloped retroviruses bud from the cell surface of T lymphocytes, they use the endocytic pathway and the internal membrane of multivesicular bodies for their assembly and release from macrophages and dendritic cells (DCs). Exosomes, physiological nanoparticles produced by hematopoietic cells, egress from this same pathway and are similar to retroviruses in terms of size, density, the molecules they incorporate and their ability to activate immune cells. Retroviruses are therefore likely to contaminate in vitro preparations of exosomes and vice versa and sucrose gradients are inefficient at separating them.