Abstract:
Presence of cytokines during periodontal inflammation has been proposed as a key factor to modulate homeostasis of periodontal tissue. Interleukin 12 (IL-12) is one of the cytokines, which its expression was found to be increased associated with the severity of periodontal destruction. However, the exact role of IL-12 in periodontitis is still unclear. As human periodontal ligament (hPDL) cells are major local cells that have an ability to respond to many immunological stimuli, this study aimed to investigate the responses of hPDL cells to exogenous IL-12 for determining the osteoimmunological and immunomodulatory effects of IL-12 on hPDL cells. HPDL cells were incubated with IL-12 in a dose and time dependent manner. The expression levels of RANKL, OPG, IFNγ, IDO, HLA-G, as well as stem cell markers were evaluated by quantitative PCR. The protein levels of RANKL, IFNγ, HLA-G and the activity of IDO were measured by ELISA, flow cytometry and enzymatic activity assay, respectively. Chemical inhibitors or neutralizing antibody were used to elucidate underlying pathways. The results of this study showed that, under the influence of IL-12, hPDL cells expressed significantly higher levels of RANKL. This induction occurred indirectly by the activation of intermediate molecule(s). Addition of suramin and EGTA suggest that the nature of the involved intermediate molecule(s) was possibly the ligand that could activate heterodimeric G protein signaling in a calcium dependent pathway. In addition, IL-12 also induced the expression of the immunosuppressive proteins: IDO and HLA-G in hPDL cells via an IFNγ dependent pathway. Moreover, the expression of the stem cells markers was also upregulated in IL-12-treated hPDL cells. Together, these data indicate both pro- and anti-inflammatory effect of IL-12 by inducing expression of RANKL and immunomodulatory properties of hPDL cells. These provide the role of IL-12 in regulating homeostasis of periodontal tissue.
