Abstract
Type I interferons are essential for host response to viral infections, while dysregulation of their response can result in autoinflammation or autoimmunity. Among IFNα (alpha) responses, 13 subtypes exist that signal through the same receptor, but have been reported to have different effector functions. However, the lack of available tools for discriminating these closely related subtypes, in particular at the protein level, has restricted the study of their differential roles in disease. We developed a digital ELISA with specificity and high sensitivity for the IFNα2 subtype. Application of this assay, in parallel with our previously described pan-IFNα assay, allowed us to study different IFNα protein responses following cellular stimulation and in diverse patient cohorts. We observed different ratios of IFNα protein responses between viral infection and autoimmune patients. This analysis also revealed a small percentage of autoimmune patients with high IFNα2 protein measurements but low pan-IFNα measurements. Correlation with an ISG score and functional activity showed that in this small sub group of patients, IFNα2 protein measurements did not reflect its biological activity. This unusual phenotype was partly explained by the presence of anti-IFNα auto-antibodies in a subset of autoimmune patients. This study reports ultrasensitive assays for the study of IFNα proteins in patient samples and highlights the insights that can be obtained from the use of multiple phenotypic readouts in translational and clinical studies.
Highlights
Type I interferons are essential for host responses to viral infections [1]
This limitation was overcome with the application of Simoa digital ELISA [11], and the use of unique monoclonal antibodies isolated from APECED patients [12] that enabled the detection of all IFNα protein subtypes with more or less equivalent and high sensitivity [13]
Patients were selected randomly from the systemic lupus erythematosus (SLE), connective tissue disease (CTD) and primary Sjogren’s syndrome (pSS) cohorts to equilibrate the number of results in each cohort and at each IFNα17/α2c protein ratio (n = 113)
Summary
Type I interferons are essential for host responses to viral infections [1]. Their dysregulation is implicated in many autoimmune dis eases, such as systemic lupus erythematosus (SLE) and primary Sjogren’s syndrome (pSS) [2], while their exact role in bacterial infection remains unclear [3]. In autoimmunity, the potential role of different IFNα subtypes is even less clear, despite their strong implication in the pathogenesis of many such diseases [10] Such studies have been restricted by the high level of sequence homology among the different subtypes, as well as the lack of tools to study them, in particular at the protein level. Until recently, IFNα protein was challenging to directly measure in human samples, with interferon stimulated genes (ISG) or functional activity used as proxy readouts. This limitation was overcome with the application of Simoa digital ELISA [11], and the use of unique monoclonal antibodies isolated from APECED patients [12] that enabled the detection of all IFNα protein subtypes with more or less equivalent and high sensitivity [13]. In contrast in active TB infection, we demonstrated an absence of plasma IFN-I [15], suggesting that the widely reported blood ISG signature most likely reflects signaling in the infected tissue [3]
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