Autoantibodies to a 140‐kd polypeptide, CADM‐140, in Japanese patients with clinically amyopathic dermatomyositis

Abstract Objective To identify novel autoantibodies specific for dermatomyositis (DM), especially those specific for clinically amyopathic DM (C‐ADM). Methods Autoantibodies were analyzed by immunoprecipitation in 298 serum samples from patients with various connective tissue diseases (CTDs) or idiopathic pulmonary fibrosis (IPF). Antigen specificity of the sera was further examined by immunoblotting and indirect immunofluorescence (IF). The disease specificity and clinical features associated with the antibody of interest were determined. Results Eight sera recognized a polypeptide of ∼140 kd (CADM‐140 autoantigen) by immunoprecipitation and immunoblotting. Immunoreactivity was detected in the cytoplasm, and indirect IF revealed a granular or reticular pattern. Anti–CADM‐140 antibodies were detected in 8 of 42 patients with DM, but not in patients with other CTDs or IPF. Interestingly, all 8 patients with anti–CADM‐140 antibodies had C‐ADM. Among 42 patients with DM, those with anti–CADM‐140 autoantibodies had significantly more rapidly progressive interstitial lung disease (ILD) when compared with patients without anti–CADM‐140 autoantibodies (50% versus 6%; P = 0.008). Conclusion These results indicate that the presence of anti–CADM‐140 autoantibodies may be a novel marker for C‐ADM. Further attention should be directed to the detection of rapidly progressive ILD in those patients with anti–CADM‐140 autoantibodies.