For morphological studies, each formvar-coated grid was positioned on top of a 5 μl droplet of the pellet containing exosomes, previously fixed for two hours at 4°C in Karnovsky fixative (2% formaldehyde + 2% glutaraldehyde) for 60 min. Afterward, the grid was sequentially positioned on three drops of 0.05 M, pH 7.3 cacodylate buffer for 5 min each. For ultrastructural immunocytochemical study, each formvar-coated grid was positioned on the top of a 5 μl drop of the pellet containing exosomes previously fixed for 2 hr at 4°C in modified Karnovsky fixative (2% formaldehyde + 0.5% glutaraldehyde) for 60 min. The grid was then put on three drops of 0.05 M, pH 7.3 cacodylate buffer for 5 min each, on 2% formaldehyde for 10 min, on three drops of 0.05 M, pH 7.3 cacodylate buffer for 5 min each, on the antibody anti-CD63 (ab23792; Abcam) diluted 1:20 for 60 min, on three drops of 1% BSA in 0.05 M, pH 7.4 Tris buffered saline buffer for 5 min each, on the gold-tagged anti-mouse antibody (Jackson Immunoresearch) diluted 1:20 for 60 min, and on three drops of 0.05 M, pH 7.4 Tris buffered saline buffer for 5 min each. Next, both for morphological and for immunocytochemical study, the grids were placed on a drop of 2% glutaraldehyde for 10 min, then on three drops of distilled water for 5 min each, on 5% uranyl acetate for 3 min, and finally on 0.013% methyl cellulose/0.04% uranyl acetate for 10 min on ice (Lasser). Between each transfer, the excess liquid was removed by holding an absorbing paper close to the side of the grid.