Autoepitopes of the 52-kd SS-A/Ro molecule

Objective. This study was undertaken to clarify the mechanisms responsible for the generation of anti–52-kd SS-A/Ro autoantibodies and to elucidate why, as has recently been reported, anti–52-kd autoantibodies preferentially recognize the denatured form rather than the native 52-kd molecule. Methods. Using a series of truncated 52-kd auto-antigens, produced as β-galactosidase fusion proteins in Escherichia coli, the B cell epitope distribution was probed with 18 anti-Ro–positive sera by immunoblotting and by enzyme-linked immunosorbent assay. Results. Nearly all the antigenicity of the molecule was found to be linked to its leucine zipper region. In a further study using 9 of the 18 sera, the antigenicity of the molecule was found to be mainly formed by multiple conformational epitopes, and one of these epitopes appeared to be universally recognized by all the sera tested. Conclusion. The recognition of multiple epitopes indicates that the Ro 52-kd antigen itself drives the autoimmunity to this molecule. Further, the concentration of the antigenicity at the leucine zipper region may explain why anti–52-kd antibodies preferentially recognize the denatured protein rather than its native form.