AB1176 ANTI-MX1 antibody: a new potential biomarker expanding the concept of interstitial pneumonia with autoimmune features (IPAF)
Authors: Y Hamano, H Kida, A Murakami, M Yanagawa, K Ueda, O Honda, Y Kato, H Takamatsu, N Tomiyama, A Kumanogoh
Journal: Annals of the Rheumatic Diseases (2017)

<h3>Background</h3> “Interstitial pneumonia with autoimmune features (IPAF)” is the updated concept instead of UCTD-ILD or lung-dominant CTD, classifying idiopathic interstitial pneumonias (IIPs) with underlying autoimmune processes by the presence of a combination of features from three domains; clinical, serologic, and morphologic domains. In IIPs, idiopathic non-specific interstitial pneumonia (INSIP) and idiopathic pulmonary fibrosis are often difficult to distinguish without surgical lung biopsy. We discovered autoantibody against myxovirus resistance protein-1 (MX1), type I interferon-inducible protein, as the biomarker specific for INSIP and associated with favorable prognosis [1]. We also reported that some of patients with collagen vascular diseases (CVDs) possess anti-MX1 antibody only when complicated with interstitial lung disease [2]. <h3>Objectives</h3> This study was aimed to investigate the association of anti-MX1 antibody positivity with IPAF category in patients with IIPs and their clinical characteristics through a cross-sectional study. We also assessed the potential of anti-MX1 antibody to expand the concept of autoimmunity in IIPs. <h3>Methods</h3> Anti-MX1 antibodies in sera of consecutive Japanese patients with chronic fibrosing IIPs (n=114), who visited the outpatient office of Osaka University Hospital from February to October 2014, were measured using ELISA. IPAF patients were classified according to the IPAF criteria in 2015 ERS/ATS statement. Comparison of the patients9 clinical characteristics and high-resolution computed tomography (HRCT) findings evaluated by three thoracic radiologists blinded to the clinical information were statistically analyzed. Serum IFNα was measured using ELISA. <h3>Results</h3> Among 114 patients with IIPs, 20 patients (17.5%) were positive for anti-MX1 antibody and 33 patients (28.9%) were classified as IPAF. When IPAF patients (n=33) were compared with non-IPAF patients (n=81), IPAF was associated with female, higher level of C-reactive protein (CRP), the presence of HRCT findings of “predominantly peribronchovascular distribution” and the absence of two HRCT findings of “honeycombing9 and `traction bronchiectasis”. Of 81 non-IPAF patients, 13 patients (16.0%) were anti-MX1 antibody positive. Among them, if anti-MX1 autoantibody were included into the existent serological domain in the IPAF criteria, 8 patients (9.9%) would be classified as IPAF. Anti-MX1 antibody positivity did not correlate with IPAF category. In non-IPAF patients, anti-MX1 antibody-positive patients were associated with female and predominantly smaller 9spared area9 when compared to anti-MX1 antibody-negative patients. Serum IFNα concentration was not associated with either anti-MX1 antibody positivity or IPAF category. <h3>Conclusions</h3> A substantial number of patients classified as non-IPAF were positive for anti-MX1 antibody, suggesting that this new autoantibody could have the potential expanding the definition of IPAF. The further studies for the clinical course and drug efficacy of anti-MX1 antibody-positive non-IPAF patients must be explored. <h3>References</h3> Hamano Y et al. Classification of idiopathic interstitial pneumonias using anti–myxovirus resistance-protein 1 autoantibody. Scientific Reports 2017 (in press). Ann Rheum Dis 2014;73(Suppl2): 1139. <h3>Disclosure of Interest</h3> Y. Hamano: None declared, H. Kida: None declared, A. Murakami Employee of: Medical &amp; Biological Laboratories Co., Ltd., Ina Laboratory, M. Yanagawa: None declared, K. Ueda: None declared, O. Honda: None declared, Y. Kato: None declared, H. Takamatsu: None declared, N. Tomiyama: None declared, A. Kumanogoh: None declared