Characterization of exosomes were identified from NDV-infected and naive HeLa cells. (A) Size and concentration of exosomes from NDV-infected and naive HeLa cells were measured using nanoparticle tracking analysis. (B) CD63, CD9, and CD81 proteins in the exosomes derived from NDV-infected and naive HeLa cells were detected by Western blotting. The expression of these proteins in naive HeLa cell lysates was used as the control. (C) Relative expression of the CD63, CD9, and CD81 proteins from (C) was analyzed with Image J software 1.8.0. β-actin was used as an internal control. (D). (a) Image of plaques formed in HeLa cells infected with NDV alone, (b) treated with exosomes derived from naive cells and then infected with NDV, and (c) treated with exosomes derived from NDV-infected cells and then infected with NDV.