Identification of interferon-inducible genes as diagnostic biomarker for systemic lupus erythematosus.

The identification of biomarkers helps to perform early diagnosis, thus benefits the outcome of patients with systemic lupus erythematosus (SLE), in which delayed treatment has been proposed as an independent adverse prognostic factor. In this study, we assessed the values of expression levels of five type I interferon (IFN)-inducible genes (LY6E, OAS1, OASL, MX1, and ISG15) and total IFN score for the diagnosis of SLE. Quantitative real-time PCR was applied to determine gene expressions at transcription level in peripheral blood from 69 SLE patients, 42 patients with other connective tissue diseases, and 26 normal controls. Expressions of five genes and IFN score, calculated according to the expressions of IFN-inducible genes, were all significantly increased in SLE patients compared to those in normal subjects and disease controls. IFN score was not related to age, gender, and the dose of steroids, but weakly correlated with SLE disease activity index. None of the gene expression was associated with concomitant infection status or elevated antibodies against Epstein-Barr (EB) virus in SLE. Both modified IFN score (calculated by the expression of three major IFN-inducible genes) and LY6E level showed good diagnostic accuracy in discriminating between SLE patients and disease controls as well as normal subjects (area under the receiver operating characteristic curve was 0.812 and 0.815, respectively), with 70-80 % specificity and 70-80 % sensitivity at the cutoff of 2.37 and 3.23. In conclusion, high IFN-inducible gene expression is constitutional for SLE patients. The modified IFN score or the LY6E level alone may serve as good biomarkers for SLE diagnosis.