Monitoring Disease Activity in Systemic Lupus Erythematosus With Single‐Molecule Array Digital Enzyme‐Linked Immunosorbent Assay Quantification of Serum Interferon‐α

Abstract

Objective. No simple or standardized assay is available to quantify interferon-α (IFNα) in routine clinical practice. Single-molecule array (Simoa) digital enzyme-linked immunosorbent assay (ELISA) technology enables direct IFNα quantification at attomolar (femtogram per milliliter [fg/ml]) concentrations. This study was undertaken to assess IFNα digital ELISA diagnostic performances to monitor systemic lupus erythematosus (SLE) activity.Methods. IFNα concentrations in serum samples from 150 consecutive SLE patients in a cross-sectional study were determined with digital ELISA and a functional biologic activity assay (bioassay). According to their Safety of Estrogens in Lupus Erythematosus National Assessment version of the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) flare composite scores, patients were divided into groups with inactive SLE (SLEDAI score of <4 or clinical SLEDAI score of 0) or active SLE (SLEDAI score of ≥4 or clinical SLEDAI score of >0), and into groups with no flare or mild/moderate flare or severe flare.Results. Based on serum samples from healthy blood donors, the abnormal serum IFNα level threshold value was 136 fg/ml. Next, using receiver operating characteristic curves for an SLE patient series that was widely heterogeneous in terms of disease activity and organ involvement, the threshold IFNα value associated with active disease was determined to be 266 fg/ml. The digital ELISA-assessed serum IFNα level was a better biomarker of disease activity than the Farr assay because its specificity, likelihood ratio for positive results, and positive predictive value better discerned active SLE or flare from inactive disease. The digital ELISA was more sensitive than the bioassay for detecting low-abnormal serum IFNα concentrations and identifying patients with low disease activity.Conclusion. Direct serum IFNα determination with a highly sensitive assay might improve monitoring of clinical SLE activity and selection of the best candidates for anti-IFNα treatment.

Circulating Interferon‐α Measured With a Highly Sensitive Assay as a Biomarker for Juvenile Inflammatory Myositis Activity: Comment on the Article by Mathian et al

“…The area under the ROC curve for IFNα concentration as a discriminator of active versus inactive juvenile IIM was 0.81 (95% confidence interval 0.70-0.92) ( Figure 1D). This value is close to the value of 0.83 previously described in SLE patients by Mathian et al (1). To distinguish active versus inactive juvenile IIM, the optimal cutoff threshold for IFNα concentration was 41.7 fg/ml, with a sensitivity and specificity of 76% and 81%, respectively (Youden index 0.57).…”

“…We read with interest the report by Dr. Mathian and colleagues in which they suggested that direct serum interferon-α (IFNα) determination with a highly sensitive assay might be useful for disease activity monitoring in systemic lupus erythematosus (SLE) (1). More generally, the identification of reactive biomarkers is highly desirable in many disease states, including idiopathic inflammatory myopathies (IIMs).…”

Ultrasensitive serum interferon-α quantification during SLE remission identifies patients at risk for relapse

“…Transcriptome analysis using microarray technology revealed upregulation of the expression of numerous IFN-stimulated genes (ISGs) in SLE patients’ peripheral blood mononuclear cells, constituting an overall ‘IFN signature’ 17 18. Many reports showed patients’ elevated serum-IFN-α levels to be associated with SLE activity and severity, suggesting that monitoring this cytokine might help physicians to better evaluate disease activity,17–35 although, unexpectedly, some clinically inactive patients have persistently elevated serum IFN-α levels 19–23 25 35. Since serum concentrations of IFN-α are usually very low and often not detectable by classic immunoassays, monitoring the expression of ISGs is used to evaluate IFN serological activity.…”

“…The single-molecule array (Simoa) assay, or digital immunoassay, is an ultrasensitive assay based on enumeration of individual enzyme-labelled immunocomplexes of proteins captured on beads in single-molecule arrays. It enables direct IFN-α quantification at attomolar concentrations,35 38–40 corresponding to a 5000-fold—increased sensitivity over classic ELISAs. We and others have shown that, at physiological concentrations, the digital immunoassay is as sensitive as ISG expression as a means to quantify IFN-α levels and simpler to perform and standardise 35 40.…”

Activities of Serum Adenosine Deaminase and its Isoenzymes in Patients with Systemic Lupus Erythematosus, Rheumatoid Arthritis, Ankylosing Spondylitis and Myasthenia Gravis

“…Notably, there was a positive correlation between tADA activity and SLE disease activity, which suggested that tADA activity might be helpful in monitoring the disease activity. Several studies have reported that interferon level (such as IFN-1α, IFN-α and IFN-λ3) were increased in SLE patients [21][22][23], which suggested the change of interferon signature were involved in SLE development. We will investigate the potential association between ADA activity and interferon in SLE patients in further study.…”