Overexpression of interferon-γ and indoleamine 2, 3-dioxygenase in systemic lupus erythematosus: relationship with the disease activity

Abstract Background: Indoleamine 2, 3-dioxygenase (IDO) is a tryptophan catabolizing enzyme which is involved in immune regulation and autoimmune disorders such as systemic lupus erythematosus (SLE). Interferon-γ (IFN-γ) is an inflammatory cytokine which is the major inducer of IDO expression. Here, we evaluated the level of IFN-γ and IDO among SLE patients in correlation with the severity of SLE. Methods: Fifty-three SLE patients and 35 age matched healthy donors were enrolled in this study. Systemic lupus erythematosus disease activity index (SLEDAI) was used to calculate the disease activity. Real-time RT-PCR and ELISA were used to evaluate the gene expression of IDO and IFN-γ plasma concentration, respectively. Results: We showed that IDO-1, IDO-2 and IFN-γ were overexpressed among SLE patients significantly (p<0.0001). There were significant positive correlations between IFN-γ with the expression of IDO-1 (r=0.722, p<0.0001) and IDO-2 (r=0.682, p<0.0001). There were also positive correlations between SLEDAI scores with IDO-1 (r=0.675, p<0.0001), IDO-2 (r=0.727, p<0.0001) and IFN-γ (r=0.907, p<0.0001). Conclusions: IDO expression and IFN-γ level could be introduced as helpful biomarkers for the determination of disease severity in SLE patients.