These results suggest that MS activates human PDL cells to express immune/defence genes encoding cytokines, chemokines, defensins and TLRs via a SIRT1 pathway. Orthodontic tooth movement is achieved by the remodelling of alveolar bone and periodontal ligaments (PDL) in response to mechanical loading [1]. The host response to orthodontic force has been described as an aseptic and transitory inflammation, Nivolumab chemical structure mediated by a variety of endogenous mediators such as cytokines and chemokines, which are involved in adaptive and innate immunity [2]. Chemokines are a superfamily of small chemotactic cytokines recognized

as regulators of inflammatory reactions, and Tyrosine Kinase Inhibitor Library high throughput the development of an appropriate immune response by co-ordinating leucocyte recruitment [3]. Mechanical stress (MS) or loading increases the production of chemokines and chemokine receptors, including interleukin (IL)-8 receptor in osteoblasts [4], IL-8 in human periodontal ligament (PDL) cells [5] and IL-11 and IL-8 in

human PDL cells [6]. A study has reported recently that chemokines such as monocyte chemoattractant protein (MCP)-1, regulated upon activation normal T cell expressed and secreted (RANTES) and macrophage inflammatory protein (MIP)-2 are up-regulated during rat orthodontic tooth movement [5]. However, an equibiaxial tensile strain of a low magnitude inhibits IL-1β-induced synthesis of IL-1β, IL-6 and IL-8 in PDL cells [7]. Furthermore, Lee et al. [8] reported that compressive stress

in PDL cells had no significant effect on IL-8 expression. In vivo, IL-1, IL-6, IL-8, IL-11 and tumour necrosis factor (TNF)-α are produced by inflammatory cells and periodontal tissue cells upon the application of orthodontic force [9]. The mechanisms involved in host immune responses to MS, however, are not completely understood. One host defence mechanism that involves activation of an innate immune response following exposure to the external environment is the production of defensins, small cationic anti-microbial Celecoxib peptides that are classified into the α- and β-defensin subfamilies [10]. Human β-defensin 1 (hBD-1) is expressed constitutively in epithelial cells, whereas hBD-2 and hBD-3 are expressed inducibly by bacteria, Candida albicans and inflammatory cytokines such as TNF-α and IL-1β[11]. Toll-like receptors (TLRs) are a transmembrane receptor family that plays a pivotal role in the modulation of immune response by recognizing pathogen-associated molecular patterns [12]. This recognition subsequently stimulates a sequence of signalling mechanisms, resulting ultimately in the production of various cytokines that serve as a link between innate and specific immune mechanisms.