OP0271 Analysis of the Autoantibody Repertoire in Idiopathic Inflammatory Myopathies Using Antigen Bead Array
Authors: A. Notarnicola, C. Mattsson, H. Idborg, C. Hellström, E. Jemseby, P.-J. Jacobsson, P. Nilsson, I.E. Lundberg
Journal: Annals of the Rheumatic Diseases (2015)

<h3>Background</h3> The Idiopathic Inflammatory Myopathies (IIM), including Polymyositis (PM), Dermatomyositis (DM) and Inclusion Body Myositis (IBM), are a group of rare systemic inflammatory diseases often associated with severe organ manifestations and premature mortality [1]. The identification of new biomarkers is needed to understand underlying biological pathways, improve diagnosis, predict prognosis and tailor treatment to the single patient. <h3>Objectives</h3> We investigated EDTA-plasma samples of IIM patients and healthy controls (HC) to discover new myositis-associated auto-antigens. <h3>Methods</h3> Planar antigen microarrays consisting of 5760 human protein fragments were used for the screening of IgG reactivity in 160 samples of patients with Systemic Lupus Erythematosus (SLE) [2]. A set of 355 antigens (Ag) was selected for verification on suspension bead array using 695 SLE samples and 278 IIM samples. The IIM samples were collected from a cohort of 245 IIM patients (91 DM, 125 PM and 29 IBM) regularly followed at the Rheumatology Unit of the Karolinska University Hospital from January 2003 until March 2014. Twenty-eight IIM patients tested positive for anti-hystidyl-tRNA-synthetase antibodies (anti-Jo-1) and 217 were anti Jo-1 negative. Samples from 41 HC were also analysed. <h3>Results</h3> Reactivity towards 70% of the 355 selected Ag was observed in more than 2% of both IIM and HC samples. Comparing the IIM and the HC groups according to the number of samples which showed reactivity towards each single Ag, reactivity towards 3 Ag was discovered with higher frequencies in the IIM samples (Fisher exact test, p&lt;0.05). We also compared each IIM subset and HC. A higher number of DM and PM samples versus HC showed reactivity towards 4 and 3 Ag, respectively. No statistically significant difference was observed between IBM and HC samples for any of the 355 Ag. Making 2 group comparisons between DM/PM/IBM subsets, a statistically significant different reactivity profile was found for 1 Ag between DM and PM, 3 Ag between DM and IBM and 4 Ag between PM and IBM. The number of reactive samples towards 5 Ag was significantly higher in the anti-Jo-1 positive compared to the anti-Jo-1 negative patients. <h3>Conclusions</h3> Auto-antigen reactivity was present both in IIM and HC samples. IIM and HC samples showed different frequencies of reactivity towards some of the selected Ag. A validation analysis is ongoing to confirm our preliminary results. <h3>References</h3> Dalakas MC. Polymyositis, dermatomyositis and inclusion-body myositis. N Engl J Med. 1991;325:1487–98. B. Ayoglu et al., Expert Rev Mol Diagn 11, 219 (Mar, 2011). <h3>Disclosure of Interest</h3> A. Notarnicola: None declared, C. Mattsson: None declared, H. Idborg: None declared, C. Hellström: None declared, E. Jemseby: None declared, P.-J. Jacobsson Grant/research support from: Astra-Zeneca, P. Nilsson: None declared, I. E. Lundberg Grant/research support from: Novartis, Servier, Astra-Zeneca och Bristol-Myers Squibb