Session Information
Session Title: Muscle Biology, Myositis and Myopathies: Myositis Autoantibodies and Disease Phenotype
Session Type: Abstract Submissions (ACR)
Background/Purpose
Anti-Melanoma Differentiation-Associated Gene 5 (MDA5) antibody is found specifically in patients with dermatomyositis (DM). This autoantibody is associated with clinically amyopathic DM (CADM) and rapidly progressive interstitial lung disease (RP-ILD) especially in eastern Asian population. An association between anti-MDA5 antibody titer measured by in-house enzyme-linked immunosorbent assay (ELISA) and disease activity has been also reported. Recently, we have established an ELISA system for detection of anti-MDA5 antibody for clinical practice use.
Objectives
To verify utility of our anti-MDA5 ELISA in a multi-center study.
Methods
Sera and clinical information were obtained from 432 patients with connective tissue disease (CTD) and 154 with Idiopathic interstitial pneumonia (IIP), who were followed at 8 participating hospitals. CTD patients included 104 with classic DM, 68 with CADM, 70 with polymyositis (PM), 43 with systemic sclerosis, 67 with systemic lupus erythematosus, 45 with rheumatoid arthritis, 20 with mixed connective tissue disease, 8 with Sjögren syndrome, and 7 with other CTD. IIP was defined as interstitial lung disease of unknown cause, in which patients did not fulfill classification criteria for any specific CTD or vasculitis. A healthy control included 123 volunteers. Anti-MDA5 ELISA utilized a recombinant protein encompassing the entire amino acid sequence of MDA5, which was expressed and purified using a baculovirus expression system. Antibody levels were shown in an index, which was calculated by optical density (OD) at 450 nm according to the following formula: (sample OD – blank OD/positive reference OD – blank OD) x 100. Immunoprecipitation (IP) assay was also conducted in patients with PM/DM (including classic DM, CADM, and PM). Comparisons between two groups were made using the chi-square test.
Results
Of 242 PM/DM samples, 10 (9.6%) with classic DM and 46 (67.6%) with CADM were positive for anti-MDA5 antibody by the gold standard IP assay. When a cutoff of the anti-MDA5 ELISA was set at 32 index based on receiver operating characteristics curve analysis in comparison with results of IP assay, analytical sensitivity and specificity of the ELISA were 98.2% and 100%, respectively. The ELISA showed an extremely high specificity, since anti-MDA5 antibody was detected in none of the patients with other CTD (including PM), those with IIP, or healthy controls. RP-ILD was more frequently found in classic DM/CADM patients with anti-MDA5 than in those without (83.6% versus 14.5%, P < 0.001).
Conclusion
This multi-center study has confirmed that a newly established ELISA for anti-MDA5 antibody is as efficient as the IP assay. This system enables easier and wider use in the detection of anti-MDA5 antibody in patients suspected to have DM and/or RP-ILD.
Disclosure:
S. Sato,
Holding a patent on anti-MDA5 antibody-measuring kit,
7;
A. Murakami,
employee of Medical & Biological Laboratories Co., Ltd.,
3;
A. Kuwajima,
employee of Medical & Biological Laboratories Co., Ltd.,
3;
K. Takehara,
None;
T. Mimori,
None;
A. Kawakami,
None;
M. Mishima,
None;
T. Suda,
None;
M. Seishima,
None;
M. Fujimoto,
None;
M. Kuwana,
Holding a patent on anti- MDA5 antibody-measuring kit. ,
7.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-multi-center-study-for-validation-of-a-new-assay-for-anti-melanoma-differentiation-associated-gene-5-mda5-autoantibody/