Temporal expression of interleukin‐22, interleukin‐22 receptor 1 and interleukin‐22‐binding protein during experimental periodontitis in rats

BACKGROUND AND OBJECTIVE: Interleukin-22 (IL-22), mainly produced by CD4+ T-helper subtypes and innate lymphoid cells at barrier surfaces, is found to involve in several diseases, including diabetes, rheumatoid arthritis, peri-implantitis and chronic rhinosinusitis with nasal polyps. The purpose of this study was to investigate histological changes and the levels of interleukin-22, interleukin-22 receptor 1 (IL-22R1) and interleukin-22-binding protein (IL-22BP) in experimental periodontitis. MATERIAL AND METHODS: Sixty male 8-week-old Sprague Dawley rats were randomly allocated to six groups of 10 rats each. In the periodontitis groups, experimental periodontitis was established and the rats were killed on days 3, 5, 7, 11 and 15 after ligation, while the rats without ligation were killed on day 0, representing the healthy control group (day 0 group). Histopathologic changes were detected by hematoxylin and eosin (H&E) staining, and alveolar bone loss was determined by micro-computed tomography (micro-CT). Tartrate-resistant acid phosphatase (TRAP) staining was used to investigate osteoclast formation. Real-time quantitative PCR (qPCR) and immunohistochemistry were used to investigate the expression and location of IL-22, IL-22R1 and IL-22BP in gingival tissues. RESULTS: H&E staining showed increasingly severe destruction of the epithelial layer between day 3 and day 7, and the hyperplasia of pocket epithelium and the formation of periodontal pockets could be detected from day 11 to day 15. Micro-CT indicated an exponential increase in alveolar bone loss from day 3 to day 11 (P < .01). Bone resorption tended to be stationary after this period. TRAP staining showed that the number of multinucleate osteoclasts peaked at day 3 (P < .001, compared with day 0) and decreased at subsequent time points between day 5 and day 15. IL-22BP was expressed strongly under steady-state conditions in epithelial cells. IL-22-positive cells could be clearly observed both in the epithelial layer and around the lamina propria, whereas IL-22R1 was mainly localized in the epithelial layer of the damage period. Real-time qPCR revealed up-regulation of IL-22 and IL-22R1, as well as down-regulation of IL-22BP in gingival tissues during the destructive phase of periodontitis. CONCLUSION: This study shows the expression and localization of IL-22, IL-22R1 and IL-22BP, as well as the relevant histopathological alterations during the development of experimental periodontitis.