MSCs induce maDCs into a novel DC population. (A) Expansion of maDCs seeded onto MSCs for 15 days. Increased cell number was obvious in culture with MSCs (top panel, maDCs from normal mice, ×400; bottom panel, maDCs from EGFP-transgenic mice, ×100). (B) Cell-cycle analysis of maDC cultured with or without MSCs. Values are the percentages of S/G2 cells. Data are representative of at least 3 independent experiments. (C) Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of maDC cultured with or without MSCs and imDC. During coculture with MSC, the nonadherent maDC with many long dendrites (without MSC group) gradually became larger with less and shorter dendrites (with MSC group). Similar to imDC, it displayed heterogenous morphology and measured on average 10 to 12 μm in diameter, possessed scattered chromatin and a relatively large nucleus. It had fewer mitochondria, endoplasmatic reticulum and vesicles, but much scattered ribosomes compared with maDC without MSC. (D) Phenotype of MSC-treated DCs. The imDC, maDC, MSC-DC (maDC cocultured with MSC for 7 days), and LPS-MSC-DC (MSC-DC stimulated by LPS for 3 days) were analyzed by flow cytometry. Dotted lines indicate background staining. Numbers in histograms indicate the mean fluorescence of each DC population. (E) Cytokine secretion profiles of maDC, MSC-DC, and MSC-DC stimulated with 500 ng/mL LPS. Data are mean (± SD) of triplicate wells. *P < .05; **P < .001. (F) MSC-DC has an enhanced phagocytic ability than maDC evaluated by OVA-FITC phagocytosis using FACS. One of at least 3 independent experiments with similar results is shown.