Figure 1: The phenotypic characterization and differentiation potential of mesenchymal stem cells (MSCs) in vitro. Mesenchymal stem cells were expanded in culture and demonstrated positive surface staining for CD44, CD73, CD90, and MHC class I, but not for CD34, CD45, MHC class II, and CD86 expression, as detected by flow cytometry. MSCs were further tested for their ability to differentiate into adipocytes, osteoblasts, and chondrocytes. Osteoblasts were identified by Alizarin red staining, lipid droplets were identified by oil-red O staining, and chondrogenic differentiation was visualized by Alcian blue staining.