Experimental studies on effects of orthodontic forces in generation of immune responses : Possible roles for immunoregulating molecules in the control of alveolar bone remodeling

Abstract: The transformation of orthodontic forces to periodontal tissues involves several biological mechanisms, which ultimately result in bone remodelling. It has been suggested that the immune system plays a role in the regulation of bone remodelling through production of immune mediators by inflammatory cells that have migrated from dilated periodontal ligament capillaries after the application of orthodontic force. In vivo induction of potentially important immunoregulatory mediators and co-stimulatory molecules were studied in response to orthodontic force to investigate their role in bone resorption. The maxillary right first molar of Wistar male rats was moved mesially by means of a closed coil spring ligated to the mesial aspect of the first molar. A strain of 500mN was applied. The maxillary contralateral molars served as controls. Using in situ hybridization with radioactive synthetic oligoneocleotide probes and immunochemistry, the induction of the pro-inflammatory cytokines IL1beta, IL-6, TNF-alpha, IFN-gamma and the anti-inflammatory cytokines IL-4 and IL-10 was examined. Also, the expression of potential chemokines as macrophage inflammatory protein-2 (MIP2), monocyte chemotactic protein-1 (MCP-1), and Regulated upon Activation, Normal Tcell Expressed and Secreted (RANTES) was studied. In addition, the role of the co-stimulatory molecules CD40 and CD40 ligand in periodontal and bone cells in orthodontically treated and untreated teeth was investigated. We demonstrated that the expression of IL-1beta mRNA and IL-6 mRNA in periodontal and bone cells located on the pressure side reached a high level on day 3 after application of the mechanical force. The numbers of cells expressing IL-1beta and IL-6 mRNA decreased on day 7, and that expression became undetectable on day 10. The control side showed little induction of IL-1beta and IL-6 mRNA. In contrast, messenger RNA for TNF-alpha was undetectable during the whole study. Thus, certain cytokines play an important role in bone remodeling after orthodontic tooth movement in the pressure zone. Furthermore, there was induction of MIP-2, MCP-1, and RANTES mRNA in response to orthodontic tooth movement on the pressure side. The maximum induction of MCP-1 and RANTES was detected on day 3. Expression of MCP-1 mRNA dominated, followed by RANTES mRNA and then MIP-2 mRNA. The number of MCP-1, RANTES and MIP-2 positive cells declined on day 7 and on day 10. This suggests that chemokines have a potential role in recruiting cells from the monocyte/macrophage cell line to the pressure zone during orthodontic movement, which may contribute to the regulation of bone remodeling. The induction of IFN-gamma was significantly higher in the experimental side than the contralateral control side and peaked on day 7, but remained high on day 10. IL-4 and IL-10 were not detected during examined time-points neither in pressure nor in contralateral control side. Considering the potential immunoregulatory roles played by IFN-gamma, the data suggest that IFN-gamma may be involved in periodontium remodeling during orthodontic tooth movement. A further proof of an adaptive immune response was the identification of CD40+ as well as CD40L expressing cells peaking at day 3 after trauma.