Comparison of anti-OJ antibody detection assays between an immunoprecipitation assay and line blot assay

A number of autoantibodies (autoAbs) are found in patients with idiopathic inflammatory myopathies, including polymyositis (PM) and dermatomyositis (DM). Abs reactive with aminoacyl-tRNA synthetases (anti-ARS) are some of the representative Abs in patients with PM/DM [1], with 8 anti-ARS being identified to date, including anti-Jo-1, anti-EJ, anti-PL-7, anti-PL-12, anti-KS, anti-OJ, anti-Ha, and anti-Zo. Although anti-synthetase syndrome has common clinical manifestations, differences have been reported in the clinical features associated with individual anti-ARS [2]. Therefore, it is of considerable clinical importance to identify each anti-ARS in patients with anti-synthetase syndrome. A commercially available enzyme-linked immunosorbent assay (ELISA) for anti-ARS has recently been developed (MESACUP® anti-ARS test, MBL, Nagoya, Japan) [3]. This kit detects any one of the five anti-ARS (anit-Jo-1, anti-PL-7, anti-PL-12, anti-EJ, and anti-KS); however, anti-ARS specificity cannot be identified because recombinant antigens are coated on the plate as a mixture. This kit also does not have the ability to detect anti-OJ, and an immunoprecipitation (IP) assay is recognized as the gold standard for identifying each anti-ARS including anti-OJ. In contrast, several studies have used a line blot (LB) assay (Myositis Profile Euroline® Blot test kit, Euroimmun, Lübeck, Germany) to identify anti-OJ [4,5]. However, comparisons of the identification of anti-OJ have not yet been conducted between the IP assay and LB assay.