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

- Anti-TIF1γ and anti-Mi-2β Ab ELISAs using a baculovirus expression system were developed and evaluated in a multicenter study.
- Anti-TIF1γ and anti-Mi-2β Ab ELISAs showed high sensitivity and specificity demonstrating their utility as easier detection systems for routine testing.
- Anti-Mi-2β Ab cross-reacts with TIF1γ through the conformational structure of TIF1γ in a cysteine residue-dependent manner due to homologous amino acid sequences within PHD.

BackgroundAutoantibodies 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.ObjectiveThis study aimed to establish enzyme-linked immunosorbent assays (ELISAs) for anti-TIF1γ and anti-Mi-2β antibodies (Abs) and to assess their utility.MethodsSerum 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 TIF1γ or Mi-2β proteins produced by a baculovirus expression system. To assess the cross-reactivity, partial-length Mi-2β proteins with or without mutations were produced and examined for reactivity.ResultsWhen compared with immunoprecipitation assay, anti-TIF1γ Ab ELISA showed 100% sensitivity and 100% specificity, while anti-Mi-2β Ab ELISA showed 100% sensitivity and 99.6% specificity. Anti-TIF1γ 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-2β Ab. Of 30 anti-TIF1γ Ab-positive DM patients, 23 (67.6%) had malignancy. Anti-Mi-2β Ab-positive serum samples exhibited modest cross-reactivity with the TIF1γ protein due to the homologous amino acid sequence containing cysteines in their plant homeodomains.ConclusionThe current study demonstrates the utility of newly established ELISAs for anti-TIF1γ and anti-Mi-2β Abs, which can serve as easier detection systems for routine testing.