Characterization of human umbilical cord mesenchymal stem cells (hucMSCs) and hucMSC-derived exosomes (hucMSC-ex). (A) Flow cytometry analyses of phenotypic markers of hucMSCs; different passages of hucMSCs showed similar results. HucMSCs were positive for CD13, CD29, CD44, CD90, CD105 and human leukocyte antigen (HLA)-I, and negative for CD34, CD45 and HLA-DR. (B) Cell lineage induced differentiation. Control cells were grown in regular medium; there were no positive cells in the cell lineage differentiation. Osteogenic differentiation of hucMSCs was shown by neutrophil alkaline phosphatase (NAP) staining; most hucMSCs were alkaline phosphatase positive. Adipogenic differentiation was analyzed by Oil-Red-O staining. After induction, hucMSCs formed numerous Oil-Red-O-positive lipid droplets (shown at original magnification, × 100). Scale bars: 100 μm. (C) Representative micrographs of transmission electron microscopy of purified hucMSC-ex and human lung fibroblast secreted exosomes (HFL-1-ex), showing a spheroid shape. The scale bar represents 100 nm. (D) Western blotting results indicated the positive expression of CD9, CD63 and CD81 proteins in exosomes derived from hucMSCs and HFL-1 cells.