ANTI-RO52 ANTIBODIES FREQUENTLY CO-OCCUR WITH ANTI-JO-1 ANTIBODIES INSERA FROM PATIENTS WITH IDIOPATHIC INFLAMMATORY MYOPATHY

We analysed 112 idiopathic inflammatory myopathy (IIM) sera for the pr esence of anti-Ro, anti-La and anti-histidyl-tRNA synthetase (Jo-1) au toantibodies, and subsequently mapped B cell epitopes on the Ro52 prot ein recognized by anti-Ro52(+) IIM sera. Sera were characterized by im munoblotting, ELISA and RNA precipitation. Both anti-Ro60 and anti-La activity was found in 4% of IIM sera. Anti-Ro52 antibodies were presen t in 20% of IIM sera. However, in anti-Jo-1(+) IIM sera (21%), the fre quency of the anti-Ro52 antibodies was found to be much higher (58%). No cross-reactivity between anti-Ro52 and anti-Jo-1 antibodies could b e detected in these sera. To learn more about the nature of anti-Ro52 antibodies occurring in IIM sera, we analysed the major epitopes of th e Ro52 protein targeted by anti-Ro52(+) IIM sera by immunoprecipitatio n 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 p otential coiled-coil domains as well as a leucine zipper motif. Althou gh 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.