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Gene‐expression studies have demonstrated increased expression of interferon (IFN)–inducible genes (IFIGs) in peripheral blood mononuclear cells (PBMCs) of many patients with systemic lupus erythematosus (SLE), with a predominant effect of type I IFN. This study examined the hypothesis that increased disease severity and activity, as well as distinct autoantibody specificities, characterize SLE patients with activation of the type I IFN pathway.Freshly isolated PBMCs from 77 SLE patients, 22 disease controls, and 28 healthy donors were subjected to real‐time polymerase chain reaction for 3 IFIGs that are preferentially induced by IFNα, and the data were used to derive IFNα scores for all individuals. Expression of IFIGs was significantly higher in SLE patients compared with disease controls or healthy donors. SLE patients with high and low IFNα scores were compared for clinical manifestations of disease, disease severity, disease activity, serologic features, and potential confounders, by bivariate and multivariate analyses.SLE patients with a high IFNα score had a significantly higher prevalence of renal disease, a greater number of American College of Rheumatology criteria for SLE, and a higher Systemic Lupus International Collaborating Clinics damage index (SDI) score than did SLE patients with low IFNα scores. Patients with high scores showed increased disease activity, as measured by lower C3 levels, hemoglobin levels, absolute lymphocyte counts, and albumin levels, and a higher anti–double‐stranded DNA (dsDNA) titer, erythrocyte sedimentation rate, and SLE Disease Activity Index 2000 score. The presence of antibodies specific for Ro, U1 RNP, Sm, and dsDNA, but not phospholipids, was significantly associated with a high IFNα score. Logistic regression analysis confirmed that renal disease, higher SDI scores, low complement levels, and presence of anti–RNA binding protein (RBP) autoantibodies were associated with a high IFNα score. Activation of the IFNα pathway defines a subgroup of SLE patients whose condition is characterized by increased disease severity, including renal disease, increased disease activity, reflected in complement activation, and autoreactivity to RBP. [ABSTRACT FROM AUTHOR]

To study the contribution of interferon‐α (IFNα) and IFNγ to the IFN gene expression signature that has been observed in microarray screens of peripheral blood mononuclear cells (PBMCs) from patients with systemic lupus erythematosus (SLE). Quantitative real‐time polymerase chain reaction analysis of healthy control PBMCs was used to determine the relative induction of a panel of IFN‐inducible genes (IFIGs) by IFNα and IFNγ. PBMCs from 77 SLE patients were compared with those from 22 disease controls and 28 healthy donors for expression of IFIGs. Expression of IFNα‐inducible genes was significantly higher in SLE PBMCs than in those from disease controls or healthy donors. The level of expression of all IFIGs in PBMCs from SLE patients with IFNα pathway activation correlated highly with the inherent responsiveness of those genes to IFNα, suggesting coordinate activation of that cytokine pathway. Expression of genes preferentially induced by IFNγ was not significantly increased in SLE PBMCs compared with control PBMCs. IFNα‐regulated gene‐inducing activity was detected in some SLE plasma samples. The coordinate activation of IFNα‐induced genes is a characteristic of PBMCs from many SLE patients, supporting the hypothesis that IFNα is the predominant stimulus for IFIG expression in lupus. [ABSTRACT FROM AUTHOR]