Daneeya Chaikeawkaew1,2, Vincent Everts3, Prasit Pavasant1,4. 1. Center of Excellence in Regenerative Dentistry, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand. 2. Oral Biology Graduate Program, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand. 3. Department of Oral Cell Biology, Academic Center of Dentistry Amsterdam, University of Amsterdam and Vrije Universiteit, Amsterdam, The Netherlands. 4. Department of Anatomy, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand.
Abstract
BACKGROUND: Toll-like receptors (TLR) are a group of receptors that play roles in the innate immune system. Human periodontal ligament cells (hPDL cells) express several TLRs, including TLR3, a nucleotide sensing receptor that recognizes double-stranded RNA from viral infection. However, its role in hPDL cells is unclear. The aim of this study was to investigate the responses of hPDL cells in terms of immunomodulation after TLR3 engagement. METHODS: HPDL cells were treated with various doses of poly I:C, a TLR3 activator. The expression of interferon-gamma (IFNγ), indoleamine 2,3 dioxygenase (IDO), and human leukocyte antigen G (HLA-G) was determined. Chemical inhibitors and small interfering RNA (siRNA) were used to confirm the role of TLR3. Coculture with human peripheral blood mononuclear cells (PBMCs) with poly I:C-activated hPDL cells was performed. RESULTS: Endosomal TLR3 in hPDL cells was observed by immunocytochemistry. Addition of poly I:C significantly enhanced the expression and secretion of IFNγ, IDO, and HLA-G. Knockdown of TLR3 using siRNA decreased the poly I:C-induced expression of these three molecules. Bafilomycin-A, an inhibitor of auto-phagosome and lysosome fusion, inhibited poly I:C-induced IDO and HLA-G expression, whereas cycloheximide and a TLR3-neutralizing antibody had no effect. In co-culture experiments, poly I:C-activated hPDL cells inhibited PBMCs proliferation and increased mRNA expression of forkhead box P3 (FOXP3), a transcription factor which is a marker of regulatory T cells. CONCLUSION: Our findings indicated that TLR3 engagement of hPDL cells induced immunosuppressive properties of these cells. Because immunosuppressive properties play an important role in tissue healing and regeneration, activation of TLR3 may help to attenuate tissue destruction by limiting the inflammatory process and perhaps initiate the healing and regeneration process of the periodontium.
BACKGROUND: Toll-like receptors (TLR) are a group of receptors that play roles in the innate immune system. Human periodontal ligament cells (hPDL cells) express several TLRs, including TLR3, a nucleotide sensing receptor that recognizes double-stranded RNA from viral infection. However, its role in hPDL cells is unclear. The aim of this study was to investigate the responses of hPDL cells in terms of immunomodulation after TLR3 engagement. METHODS:HPDL cells were treated with various doses of poly I:C, a TLR3 activator. The expression of interferon-gamma (IFNγ), indoleamine 2,3 dioxygenase (IDO), and human leukocyte antigen G (HLA-G) was determined. Chemical inhibitors and small interfering RNA (siRNA) were used to confirm the role of TLR3. Coculture with human peripheral blood mononuclear cells (PBMCs) with poly I:C-activated hPDL cells was performed. RESULTS: Endosomal TLR3 in hPDL cells was observed by immunocytochemistry. Addition of poly I:C significantly enhanced the expression and secretion of IFNγ, IDO, and HLA-G. Knockdown of TLR3 using siRNA decreased the poly I:C-induced expression of these three molecules. Bafilomycin-A, an inhibitor of auto-phagosome and lysosome fusion, inhibited poly I:C-induced IDO and HLA-G expression, whereas cycloheximide and a TLR3-neutralizing antibody had no effect. In co-culture experiments, poly I:C-activated hPDL cells inhibited PBMCs proliferation and increased mRNA expression of forkhead box P3 (FOXP3), a transcription factor which is a marker of regulatory T cells. CONCLUSION: Our findings indicated that TLR3 engagement of hPDL cells induced immunosuppressive properties of these cells. Because immunosuppressive properties play an important role in tissue healing and regeneration, activation of TLR3 may help to attenuate tissue destruction by limiting the inflammatory process and perhaps initiate the healing and regeneration process of the periodontium.