Human amnion mesenchymal cells negative co-stimulatory molecules PD-L1 expression and its capacity of modulating microglial activation of CNS.

The objective of this study is to investigate the negative immunomodulatory capacity of human amniotic mesenchymal cells (AMSCs) and their possible intrinsic mechanism, by which we can confirm that they modulate microglial activation of central nervous system from multiple perspectives at the molecular level. The identification of the immune phenotype of AMSCs and microglial cells was executed by immunohistochemical methods and flow cytometry. Meanwhile, the influence and mechanism of amniotic mesenchymal cells in vitro on proliferation, cell cycle, and cytokine release of activated microglia (MI) would be detected by ELISA, β-liquid scintillation counting method, and flow cytometry. Human amnion mesenchymal cells highly expressed negative co-stimulatory molecules PD-L1, while its ligand PD1 was expressed with high level by activated MI. When adding the PD-L1mAb to the mixed culture system composed of AMSCs and activated MI, the proliferation inhibitory effect and the cycle-blocking effect produced by the former on the latter would be partially reversed; at the same time, the impact of the latter cytokine secretion would be adjusted. As a conclusion, AMSCs play inhibitory effects on microglial activation, proliferation, and immune effects partially through the PD-L1-PD1 signaling pathways.