CD40-CD40L expression during orthodontic tooth movement in rats

The aim of this study was to investigate the expression of the costimulatory molecules CD40 and CD40L in periodontal and bone cells in orthodontically treated and untreated teeth using immunohistochemistry. The upper first molars were moved mesially by a fixed appliance. In the experimental group, CD40+ cells were detected at both the tension and the resorption sides in fibroblast-, macrophage-, and dendritic-like cells. The staining was more pronounced on the resorption side. The strongest expression was observed on day 3, decreased on day 7, and reached a low level on day 10 after application of orthodontic force. In contrast, in the treated animals CD40 ligand was expressed on day 3, the expression was enhanced on day 7, and was more pronounced on day 10. CD40L-expressing cells were found predominantly around hyalinized tissue in the resorption zone and the tension areas of the distal root. CD40L was expressed in the bone marrow cells in the pressure zone. In the tension side, some cells of the cellular cementum expressed CD40L. The expression of CD40 and CD40L was low in untreated teeth. These results suggest that CD40-CD40L interaction appears to be an active process during orthodontic tooth movement and that orthodontic force induces T-cell activation. Such activation may be involved in the induction of inflammatory mediators and subsequent bone remodeling. In addition, this may lead to the generation of anti-inflammatory mediators that support defense mechanisms against root resorption, which depend on the type of immune response that is induced regarding CD40-CD40L expression.