To identify the autoantigen recognized by the autoantibody that is associated with clinically amyopathic dermatomyositis (C-ADM) and rapidly progressive interstitial lung disease (ILD).


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.


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.


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.