Objective: To investigate the expressions of programmed death ligand 1 (PD-L1) and PD-L2 in human placenta-derived mesenchymal stem cells (hPMSCs) and their mediated immunoregulation on the secretion of IL-17 of peripheral blood T cells.
Methods: hPMSCs were isolated from mature human placenta by the method of enzyme digestion. The cells were cultured and expanded in vitro, and after the third passage, they were used in phenotyping and differentiation experiments. The expressions of PD-L1 and PD-L2 were detected by RT-PCR, laser-scanning confocal microscopy (LSCM) and flow cytometry. Specific siRNAs were transfected into hPMSCs via cathodolyte liposome transfection method to silence the expressions of PD-L1 and PD-L2. T cells were sorted from healthy peripheral blood by gradient centrifugation. IL-17 secretion of T cells activated by PMA was detected by intracellular staining after the expressions of PD-L1 and PD-L2 were silenced.
Results: Besides PD-L1, hPMSCs also highly expressed PD-L2, which could be silenced effectively by specific siRNA. Intracellular staining showed that hPMSCs up-regulated the secretion of IL-17, which was further up-regulated after PD-L1 or/and PD-L2 had been silenced and there were overlapping roles of PD-L1 and PD-L2 in inhibiting IL-17 secretion by T cells.
Conclusion: PD-L1 and PD-L2 expressed on hPMSCs could inhibit the hPMSCs-mediated up-regulation on the expression of IL-17 secreted by peripheral blood T cells.