EPITOPE MAPPING OF THE 52-KD RO SSA AUTOANTIGEN/

Autoantibodies to Ro/SSA are commonly found in sera of patients with s ystemic lupus erythematosus (SLE) and primary Sjogren's syndrome. The presence of these antibodies is related to lymphopenia, photosensitive dermatitis, and pulmonary and renal disease, suggesting that they hav e an immunopathologic role [1-6]. We previously isolated a cDNA clone which encodes the 52-kD human Ro/SSA protein. In this study we have de termined the number and location of epitopes recognized by SLE sera us ing recombinant proteins encoded by the full-length or overlapping sub clones of this cDNA. An immunodominant epitope was detected using West ern blots and ELISA on the NH2-terminal side of this protein's putativ e leucine zipper. The data suggest that 11 amino acids are critical fo r the recognition of this molecule by these autoantibodies. Although t he titres of anti-52-kD Ro/SSA antibodies vary between different patie nt sera, no heterogeneity in the location of antigenic epitopes to whi ch their autoantibodies bound was detected. This homogeneous pattern o f reactivity to a single rather than multiple regions of this protein is unusual for lupus autoantigens which have been identified, and sugg ests that these antibodies may have arisen as by a cross-reaction to a n epitope on another molecule.