Interferon-stimulated gene 15 expression in systemic lupus erythematosus. Diagnostic value and association with lymphocytopenia

Background. The aim of this study was to (a) assess the relationship between interferon-stimulated gene 15 (ISG15) expression and clinical manifestations of systemic lupus erythematosus (SLE) and (b) investigate the diagnostic value of ISG15 in SLE. Patients and methods. The study comprised 28 patients newly diagnosed with SLE, 10 patients with undifferentiated connective tissue disease, and 22 healthy volunteers. Of the SLE patients, 14 were chosen randomly to be followed up for 4 weeks. ISG15 expression in whole blood cells was determined by quantitative polymerase chain reaction. Clinical and laboratory parameters were recorded at baseline and after treatment. Results. The ISG15 mRNA level was higher in whole blood cell counts of SLE patients when compared with the disease control and healthy control groups. Moreover, it was correlated with SLE disease activity as assessed via the SLE disease activity index, serositis, and anemia at baseline. ISG15 expression correlated with lymphocytopenia in active SLE patients before treatment. On receiver operating characteristic curve analysis, the area under the curve for ISG15 expression was 0.826 (p = 0.000015). Conclusion. ISG15 expression is relatively high in SLE patients and correlates with disease activity before treatment. ISG15 expression is higher in SLE patients with lymphocytopenia before treatment.