Serum IFNα2 measured by single-molecule array associates with systemic disease manifestations in Sjögren's syndrome

OBJECTIVES: Type I IFN (IFN-I) activation is a prominent feature of primary SS (pSS), SLE, and SSc. Ultrasensitive single-molecule array (Simoa) technology has facilitated the measurement of subfemtomolar concentrations of IFNs. Here, we aimed to measure IFNα2 in serum from pSS, SLE, and SSc using a Simoa immunoassay and correlate these levels to blood IFN-stimulated gene (ISG) expression and disease activity.

METHODS: Serum IFNα2 was measured in patients with pSS (n = 85; n = 110), SLE (n = 24), and SSc (n = 23), and healthy controls (HC; n = 68) using an IFNα Simoa assay on a HD-X analyser. IFN-I pathway activation was additionally determined from serum by an IFN-I reporter assay and paired samples of whole blood ISG expression of IFI44, IFI44L, IFIT1, IFIT3, and MxA by RT-PCR or MxA-ELISA.

RESULTS: Serum IFNα2 levels were elevated in pSS (median=61.3 fg/mL) compared to HC (median ≤5 fg/mL; p < 0.001) and SSc (median=11.6 fg/mL; p = 0.043), lower compared to SLE (median=313.5 fg/mL; p = 0.068), and positively correlated with blood ISG expression (r = 0.66-0.94; p < 0.001). Comparable to MxA-ELISA (AUC=0.93), IFNα2 measurement using Simoa identified pSS with high ISG expression (AUC=0.90) with 80-93% specificity and 71-84% sensitivity. Blinded validation in an independent pSS cohort yielded a comparable accuracy. Multiple regression indicated independent associations of autoantibodies, IgG, HCQ treatment, cutaneous disease and history of extraglandular manifestations with serum IFNα2 concentrations in pSS.

CONCLUSION: Thus, Simoa serum IFNα2 reflects blood ISG expression in pSS, SLE, and SSc. In light of IFN-targeting treatments, Simoa could potentially be applied for patient stratification or retrospective analysis of historical cohorts.