Anti-Ro52 antibodies frequently co-occur with anti-Jo-1 antibodies in sera from patients with idiopathic inflammatory myopathy

We analysed 112 idiopathic inflammatory myopathy (IIM) sera for the presence of anti-Ro, anti-La and anti-histidyl-tRNA synthetase (Jo-1) autoantibodies, and subsequently mapped B cell epitopes on the Ro52 protein recognized by anti-Ro52(+) IIM sera. Sera were characterized by immunoblotting, ELISA and RNA precipitation. Both anti-Ro60 and anti-La activity was found in 4% of IIM sera. Anti-Ro52 antibodies were present in 20% of IIM sera. However, in anti-Jo-1(+) IIM sera (21%), the frequency of the anti-Ro52 antibodies was found to be much higher (58%). No cross-reactivity between anti-Ro52 and anti-Jo-1 antibodies could be detected in these sera. To learn more about the nature of anti-Ro52 antibodies occurring in IIM sera, we analysed the major epitopes of the Ro52 protein targeted by anti-Ro52(+) IIM sera by immunoprecipitation of in vitro translated Ro52 deletion mutants. The major epitope was mapped in the region bordered by amino acids 126 and 252. This part of the protein includes a long alpha-helical region which contains two potential coiled-coil domains as well as a leucine zipper motif. Although no difference in Ro52 epitope recognition between anti-Jo-1(+) and anti-Jo-1(-) IIM sera could be observed, our results suggest that the autoimmune response against Ro52 and Jo-1 in IIM patients is coupled.