RNA helicase encoded by melanoma differentiation-associated gene 5 is a major autoantigen in patients with clinically amyopathic dermatomyositis: Association with rapidly progressive interstitial lung disease.
OBJECTIVE
To identify the autoantigen recognized by the autoantibody that is associated with clinically amyopathic dermatomyositis (C-ADM) and rapidly progressive interstitial lung disease (ILD).


METHODS
An anti-CADM-140 antibody-positive prototype serum sample was used to screen a HeLa cell-derived complementary DNA (cDNA) library. Selected cDNA clones were further evaluated by immunoprecipitation of their in vitro-transcribed and in vitro-translated products using anti-CADM-140 antibody-positive and anti-CADM-140 antibody-negative sera. The lysates of COS-7 cells transfected with the putative antigen were similarly tested. An enzyme-linked immunosorbent assay (ELISA) to detect the anti-CADM-140 antibody was established using a recombinant CADM-140 antigen, and its specificity and sensitivity for C-ADM and rapidly progressive ILD were assessed in 294 patients with various connective tissue diseases.


RESULTS
By cDNA library screening and immunoprecipitation of in vitro-transcribed and in vitro-translated products, we obtained a cDNA clone encoding melanoma differentiation-associated gene 5 (MDA-5). The anti-CADM-140 antibodies in patients' sera specifically reacted with MDA-5 protein expressed in cells transfected with full-length MDA-5 cDNA, confirming the identity of MDA-5 as the CADM-140 autoantigen. The ELISA, using recombinant MDA-5 protein as the antigen, showed an analytical sensitivity of 85% and analytical specificity of 100%, in comparison with the "gold standard" immunoprecipitation assay, and was useful for identifying patients with C-ADM and/or rapidly progressive ILD.


CONCLUSIONS
Given that RNA helicase encoded by MDA-5 is a critical molecule involved in the innate immune defense against viruses, viral infection may play an important role in the pathogenesis of C-ADM and rapidly progressive ILD. Moreover, our ELISA using recombinant MDA-5 protein makes detection of the anti-CADM-140 antibody routinely available.
Sato
Shinji
S
Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan.
Hoshino
Kana
K
Satoh
Takashi
T
Fujita
Tomonobu
T
Kawakami
Yutaka
Y
Fujita
Takashi
T
Kuwana
Masataka
M
D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000097:blood / Q000276:immunology; D001324:Autoantigens / Q000097:blood / Q000276:immunology*; D019556:COS Cells; D016022:Case-Control Studies; D002522:Chlorocebus aethiops; D053487:DEAD-box RNA Helicases / Q000097:blood / Q000235:genetics / Q000276:immunology*; D018076:DNA, Complementary / Q000097:blood / Q000235:genetics; D003882:Dermatomyositis / Q000097:blood / Q000276:immunology*; D018450:Disease Progression; D006801:Humans; D000072640:Interferon-Induced Helicase, IFIH1; D017563:Lung Diseases, Interstitial / Q000097:blood / Q000276:immunology*; D020365:RNA Helicases / Q000097:blood / Q000235:genetics / Q000276:immunology*; D012680:Sensitivity and Specificity; D014162:Transfection
D000888:Antibodies, Anti-Idiotypic; D001324:Autoantigens; D018076:DNA, Complementary; C452815:IFIH1 protein, human; D053487:DEAD-box RNA Helicases; D000072640:Interferon-Induced Helicase, IFIH1; D020365:RNA Helicases