Localization of Toll-like receptors in periapical lesion

Objectives: Toll-like receptors (TLRs) are important factors in innate immune responses, and these signals relate to induce RANKL expression in osteoblast, which results in enhancing osteoclast formation and bone loss. The present study investigated the localization of TLR-2-, TLR-4-, RANKL-positive cells in experimental periapical lesion to elucidate the periapical bone loss mechanism. Methods: Eighteen 7-week-old female BALB/c mouse were used. Pulp infection was induced by pulpal exposure with 1/4 round bar, experimental jaws were obtained and prepared on days 1, 3 and 7. TLR-2-, TLR-4- and RANKL-positive cells were investigated with immunohistochemistry by ABC methods. Results: TLR-4- and RANKL- positive osteoblast were detected in periapical alveolar bone surface on day 1, and numerous osteoclast were detecteded around periapical lesion on day 7. Conclusion: These results suggested that TLR-4 and RANKL-positive osteoblast may be up-regulated during the early inflammation stage, and those cells induced osteoclast differentiation in periapical lesion.