P.08Interferon level assessed by ultrasensitive detection technology in myositis patients: a promising biomarker of disease activity in dermatomyositis and anti-synthetase syndrome

Inflammatory idiopathic myopathies (IIM) are a heterogeneous group of disorders ranging from muscle specific auto-immune diseases to systemic ones (dermatomyositis (DM), anti-synthetase syndrome (ASyS), immune-mediated necrotizing myopathy (IMNM) and inclusion body myositis (IBM)). Recent insight into DM pathogenesis highlighted the role of type I interferon (IFN) and the level of IFN-pathway activity is linked to those of the disease. The aim of this study was to measure IFN-α, β and γ seric level in the different groups of myositis using an ultrasensitive detection technology to evaluate IFN-α as disease activity biomarker. One hundred and fifty-two patients (50 DM, 46 ASS, 32 IMNM and 24 IBM) and 32 age-matched healthy controls were included. Patient's characteristics were similar in all groups, but IBM patients were older (69.3± 8.3). IFN-α levels were higher in DM (m[IQR]= 0.07 pg/ml [0.03-0.23]) p<0.005) and ASyS groups (m[IQR]= 0.07 [0.02-0.16]) p<0.05) compare to controls (m[IQR]= 0.02 [0.01-0.05]) but not in the IMNM (m[IQR]= 0.03 [0.01-0.09]) or IBM (m[IQR]= 0.02 [0.02-0.03]). IFN-α levels were correlated to disease activity in DM (r=0.76, p<0.0001) and ASyS groups (r=0.55, p<0.005). The accuracy of IFN-α level to discriminate active and non-active disease was excellent attested by an area of 0.88 under the ROC-curve (AUC). For an IFN-α level above 0.11 pg/ml, the sensitivity was 75% and specificity was 96%. In ASyS group, the accuracy of the test was also good (AUC=0.85) Se was 64.7% and Sp 88.5% for an IFN-α level cut-off at 0.12 pg/ml. IFN-β was increased only in DM patient with a good correlation with disease activity (R= 0.60, p<0.001). IFN-γ was increased in all IIM but with a mild correlation with disease activity. IFN-α could be a good biomarker of disease activity, especially in DM. In perspective, a better understanding of these pathologies could allow us to select targeted therapies.