Indoleamine 2,3-dioxygenase expression in human gingival fibroblasts

Abstract

Indoleamine 2,3-dioxygenase (IDO) is an intracellular tryptophan-metabolizing enzyme with immunosuppressive characteristics. Periodontitis is the chronic inflammatory disease that destroys the tooth-supporting structures. Gingival fibroblasts are major cell types in periodontal tissues which play a crucial role in maintaining connective tissue integrity and regulating local inflammatory responses. The purpose of this research is to study the regulation of IDO expression in primary cultures of human gingival fibroblasts (HGF) from healthy gingival tissues. HGF cells were treated with inflammatory cytokines and mediators. IDO mRNA expression and enzymatic activity was determined by reverse transcription-polymerase chain reaction (RT-PCR) and by spectrophotometric method, respectively. It was shown that HGF cells did not constitutively express IDO. IFN-[gamma] strongly induced IDO expression in HGF cells. IL-1[beta], TNF-[alpha], as well as lipopolysaccharides (LPS) from P. gingivalis were able to induce IDO expression, however, at a lower extent. IFN-[gamma], TNF-[alpha], and P. gingivalis LPS appeared to induce IDO expression in a dose-dependent manner. Stimulation of HGF cells with combination between IFN-[gamma] and other agents resulted in increased expression of IDO, as compared to IFN-[gamma] alone. IDO activity was significantly increased in HGF treated with IFN-[gamma]. HGF cells treated with IL-1[beta], TNF-[alpha], and P. gingivalis LPS did not show significant increased in IDO activity. Combinations of IFN-[gamma] and IL-1[beta] as well as IFN-[gamma] and TNF-[alpha] significantly increased IDO activity, as compared to that of IFN-[gamma] alone. In conclusion, we showed that IDO expression and activity in HGF cells was regulated by several inflammatory cytokines and mediators. Induction of IDO expression in HGF cells by these mediators may play a role in the pathogenesis of periodontal diseases.