Inhibitory effects of exosomes derived from human dental pulp mesenchymal stem cells on the maturation and function of dendritic cells in mice
Objective 
To investigate the effects of exosomes derived from human dental pulp mesenchymal stem cells (hDPSC-exosomes) on the maturation and function of dendritic cells (DC) stimulated by lipopolysaccharide (LPS), and to evaluate their regulatory effects on the immune system. 
 
 
Methods 
Adult permanent teeth-derived dental pulp mesenchymal stem cells were cultured in vitro to extract exosomes in the cell culture medium. The morphology and sizes of the exosomes were observed under transmission electron microscopy. Expression of CD9 and CD63 on the surface of the exosomes was detected by Western blot. PBS, LPS and LPS+ hDPSC-exosomes were respectively used to stimulate mouse bone marrow-derived dendritic cells (DC2.4) for 24 h. A blank control group was set up accordingly. Expression of co-stimulatory molecules and cytokine secretion were detected by flow cytometry and ELISA, respectively. Expression of TLR2, TLR4 and NF-κB at mRNA level was detected by RT-PCR. Changes in the functions of DC were evaluated by mixed lymphocyte reaction (MLR). 
 
 
Results 
Adult permanent teeth-derived dental pulp mesenchymal stem cells were successfully isolated. Up-regulated CD73 and CD90, and down-regulated CD45 were detected on the surface of the cells. Under electron microscopy (SEM), hDPSC-exosomes showed round or oval microcapsule bodies about 50-80 nm in diameter with positive surface markers of CD9 and CD63. hDPSCs-exosomes could significantly reduce the LPS-induced expression of co-stimulatory molecules CD11c and CD86 on DC surface. Moreover, hDPSCs-exosomes increased TGF-β expression and decreased IL-4. They could also significantly inhibit the proliferation of splenic lymphocytes that was induced by DC after LPS stimulation. Compared with the blank control group, hDPSC-exosomes could promote the expression of TLR2 and TLR4 on DC surface and up-regulate the expression of NF-κB. 
 
 
Conclusions 
This study showed that hDPSC-exosomes could inhibit the activation and functional maturation of DC, promote the development towards tolerant DC through TLR-NF-κB signaling pathway, and induce immune tolerance to regulate immune balance. 
 
 
Key words: 
Dental pulp mesenchymal stem cell; Exosome; Dendritic cell; Immunoregulation