Isolation and characterization of prom1-exo from FEMX-I cells. A. Scheme of isolation of “classical” microvesicles by differential centrifugation and of prom1-exo by a combination of differential centrifugation, filtration and immuno-magnetic separation. B. Microvesicle tracking analysis shows size distribution of a “classical” ultracentrifugation-based preparation of microvesicles and a prominin-1-based immunomagnetic preparation (prom1-exo), both from serum-free culture medium of the human FEMX-I metastatic melanoma cell line. Both preparations were stained with the membrane dye PKH67 and fluorescence analyzed by a 488 nm laser. Nanotracking analysis gives mean peak intensities of 80 and 120 nm for microvesicles and 90 nm for exosomes, respectively. The persistent binding of magnetic beads (50 nm) to the prominin-1 microvesicles resulted in an over-estimation of their size distribution.