This study was conducted to observe the immunohistochemical localization of high-mobility group box 1 (HMGB1) and its receptor, Toll-like receptor 4 (TRL4), in the development of periapical lesions induced in rats. The possible role of these molecules in the pathogenesis of periapical lesions was also explored.Methods
Periapical lesions developed within 35 days after mandibular first molar pulp exposure in Wistar rats. The animals were randomly killed at 0, 7, 14, 21, 28, and 35 days after pulp exposure. The jaws that contained the first molar were obtained and prepared for histologic analysis, enzyme histochemistry, immunohistochemistry, and double immunofluorescence staining.Results
From day 0 to 35, the areas of periapical bone loss increased and appeared to be stabilized on day 35. A few HMGB1-positive, TLR4-positive cells and osteoclasts could be observed on day 7. From day 7 to 28, the HMGB1 and TLR4 protein expression increased and subsequently remained stable. The number of osteoclasts multiplied from day 0 to 14 and then gradually decreased from day 14 to 35. Double immunofluorescence staining results showed HMGB1-positive, TLR4-positive cells around periapical lesions surrounding the apical foramen.Conclusions
Thus, HMGB1 and TLR4 may be associated with the pathogenesis of the periapical lesions.