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Abstract
Background
IL-32 was recently found to be elevated in the tissue of rheumatoid arthritis and inflammatory bowel disease. Periodontitis is a chronic inflammatory disease caused by polymicrobial infections that result in soft tissue destruction and alveolar bone loss. Although IL-32 is also thought to be associated with periodontal disease, its expression and possible role in periodontal tissue remain unclear. Therefore, this study investigated the expression patterns of IL-32 in healthy and periodontally diseased gingival tissue. The expression of IL-32 in cultured human gingival fibroblasts (HGF) as well as effects of autocrine IL-32 on IL-8 production from HGF were also examined.
Methods
Periodontal tissue was collected from both healthy volunteers and periodontitis patients, and immunofluorescent staining was performed in order to determine the production of IL-32. Using real-time PCR and ELISA, mRNA expression and protein production of IL-32 in HGF, stimulated by Porphyromonas gingivalis (Pg), were also investigated.
Results
Contrary to our expectation, the production of IL-32 in the periodontitis patients was significantly lower than in the healthy volunteers. According to immunofluorescent microscopy, positive staining for IL-32 was detected in prickle and basal cell layers in the epithelium as well as fibroblastic cells in connective tissue. Addition of fixed Pg in vitro was found to suppress the otherwise constitutive expression of IL-32 mRNA and protein in HGF. However, recombinant IL-32 in vitro inhibited the expression of IL-8 mRNA by HGF stimulated with Pg. Interestingly, anti-IL-32 neutralizing antibody upregulated the IL-8 mRNA expression in non-stimulated HGF, indicating that constitutive expression of IL-32 in HGF suppressed IL-8 mRNA expression in the absence of bacterial stimulation.
Conclusion
These results indicate that IL-32 is constitutively produced by HGF which can be suppressed by Pg and may play a role in the downregulation of inflammatory responses, such as IL-8 production, in periodontal tissue.
Acknowledgements
This research was supported by a Grant-in-Aid for the Encouragement of Young Scientists (B) 22792085 from the Japan Society for the Promotion of Science and by an NIH grant DE-018499 from the NIDCR (Kawai). We would like to thank Mr. Tomoya Matsumoto (Keyence, Osaka, Japan) for his helpful advice and technical support.