Background “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 . We also reported that some of patients with collagen vascular diseases (CVDs) possess anti-MX1 antibody only when complicated with interstitial lung disease .
Objectives 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.
Methods 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 patients' 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.
Results 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 “honeycombing' 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 'spared area' when compared to anti-MX1 antibody-negative patients. Serum IFNα concentration was not associated with either anti-MX1 antibody positivity or IPAF category.
Conclusions 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.
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.
Disclosure of Interest Y. Hamano: None declared, H. Kida: None declared, A. Murakami Employee of: Medical & 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