MALP-2, an agonist of TLR6, promotes the immune status without affecting the differentiation capacity of umbilical cord mesenchymal stem cells.

Mesenchymal stem cells (MSCs) are increasingly used in cell-based therapy due to their multiple differentiation capacity, low expression of co-stimulatory factors and immunosuppressive effect. However, accumulating studies reported the recognition and rejection of engrafted MSCs, which eventually led to the fail of clinical trials. Toll-like receptors (TLRs) are important in mediating the immune response. In the present study, macrophage-activated lipopeptide-2 (MALP-2) was introduced to activate the TLR6 pathway in umbilical cord MSCs (UCMSCs). PBLs isolated from healthy volunteers were co-cultured with UCMSCs to measure whether activation of TLR6 of UCMSCs could stimulate immune responses. Reverse transcription-quantitative polymerase chain reaction and immunohistochemistry were performed to detect pro-inflammatory molecules and differentiation status of UCMSCs, respectively. The results indicated that activation of TLR6 in UCMSCs increased the proliferation of peripheral blood leukocytes (PBLs) and enhanced the release of lactate dehydrogenase in damaged UCMSCs, which confirmed the role of TLR6 in promoting the immunogenicity of UCMSCs. Furthermore, quantitative polymerase chain reaction demonstrated that the expression of proinflammatory molecules (including IL-1β, IL-6, IL-8, IL-10, CCL1 and CCL4) was induced, whereas the expression of stem cell markers (Klf4 and Nanog) was inhibited. The differentiation results indicated that activation of TLR6 had no effect on the differentiation capacity of UCMSCs. All these findings suggest that stimulation of TLR6 pathway may increase the immunogenicity of UCMSCs in in vitro detections. In conclusion, the results of the current study indicated a new role of TLR6 in regulating the biological function of UCMSCs.