Expression of IFN-α signature genes. Expression of the interferon (IFN)-α responsive genes (a) IFI44, (b) IFIT1, and (c) PRKR was assessed using semiquantitative reverse transcription PCR. Peripheral blood mononuclear cells (PBMCs) were isolated from patients with systemic lupus erythematosus (n = 27; 9 with active and 18 with inactive disease) and healthy control individuals (n = 17). The expression of each gene is presented relative to β-actin expression. The solid bars represent the mean value for each experimental group. Statistical significance was analyzed using Student's t-test.