Enzyme-linked immunosorbent assays for detection of anti-transcriptional intermediary factor-1 gamma and anti-Mi-2 autoantibodies in dermatomyositis

Background: Autoantibodies against transcriptional intermediary factor 1 (TIF1) and Mi-2 are selectively detected in patients with dermatomyositis (DM). To measure these antibodies readily, the development of reliable ELISA systems has been needed. Objective: This study aimed to establish enzyme-linked immunosorbent assays (ELISAs) for anti-TIF1 gamma and anti-Mi-2 beta antibodies (Abs) and to assess their utility. Methods: Serum samples were obtained from 104 patients with classic DM, 68 with clinically amyopathic DM (CADM) and 70 with polymyositis, who were followed up at 8 medical centers across Japan. Serum samples from 190 patients with other connective tissue diseases (CTDS) and 123 healthy individuals were also assessed. Serum antibody levels were examined by ELISAs coated with full-length TIF1 gamma or Mi-2 beta proteins produced by a baculovirus expression system. To assess the cross-reactivity, partial-length Mi-2 beta proteins with or without mutations were produced and examined for reactivity. Results: When compared with immunoprecipitation assay, anti-TIF1 gamma Ab ELISA showed 100% sensitivity and 100% specificity, while anti-Mi-2 beta Ab ELISA showed 100% sensitivity and 99.6% specificity. Anti-TIF1 gamma Ab was positive in 30 (28.8%) with classic DM and 4 (5.9%) with CADM, whereas 14 (13.5%) with classic DM, but none with CADM, were positive for anti-Mi-213 Ab. Of 30 anti-TIF1 gamma Ab-positive DM patients, 23 (67.6%) had malignancy. Anti-Mi-2 beta Ab-positive serum samples exhibited modest cross reactivity with the TIF1 gamma protein due to the homologous amino acid sequence containing cysteines in their plant homeodomains. Conclusion: The current study demonstrates the utility of newly established ELISAs for anti-TIF1 gamma and anti-Mi-2 beta Abs, which can serve as easier detection systems for routine testing. (C) 2016 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.