Isolation of HMEC exosomes. (A) Immunoblots of sucrose gradient samples for the endothelial marker CD31/PECAM-1 (upper panel) and exosome marker flotillin-1 (lower panel) are shown. (B) Transmission electron microscopic analysis of exosomes is shown. Bar represents 250 nm. (C) Endothelial cells after 2 hours of incubation with PKH67 fluorescently labeled exosomes are shown (PKH67 in green, DAPI in blue). Bar represents 50 μm. Images were recorded at RT on an Olympus CX60 microscope using an Olympus UPlan Fl 20×/0.05 objective lens that was coupled to an Olympus DP71 camera operated using CellP software. Brightness was enhanced using Adobe Photoshop software.