Immunohistochemical localization of IL-17 in induced rat periapical lesions

Interleukin (IL)-17 is a member of a novel family of proinflammatory cytokines produced almost exclusively by a newly recognized subclass of activated T cells called "Th17" cells. From an endodontic perspective, IL-17 potently regulates cells of the innate immune system, serving as an important bridging molecule between the adaptive and innate immune systems. The purpose of this study was to investigate the immunohistochemical localization of IL-17 during the development of periapical lesions in rats. Periapical lesions developed within 28 days after mandibular first molar pulp exposure in Sprague-Dawley rats. The animals were randomly sacrificed at 0, 7, 14, 21, and 28 days after pulpal exposure. The jaws that contained the first molar were obtained and routinely prepared for histologic analysis, immunohistochemistry, and enzyme histochemistry. From day 0 to day 28, the number of IL-17-positive cells and neutrophils ascended and peaked on day 28. Osteoclast numbers substantially multiplied from day 0 to day 14 and then gradually decreased from day 14 to day 28. In addition, the osteoclast decrease contrasted with the increased number of IL-17-positive cells and neutrophils. These findings showed that IL-17 could be observed and might possibly be involved in the inflammatory response and bone resorption of periapical tissues as well as associated with periapical lesion pathogenesis.