Can B cell epitopes of 60 kDa Ro distinguish systemic lupus erythematosus from Sjogren's syndrome?

Antibodies binding components of the Ro/La (or SSA/SSB) ribonucleoprotein p article are found in the sera of patients with systemic lupus crythematosus (SLE) and Sjogren's syndrome (SS) as well as mothers who give birth to bab ies with neonatal lupus. Anti-La occurs in a subset of sera that contain an ti-Ro, and anti-La is found more commonly in sera of patients with SS than in sera from SLE patients. The fine specificity of autoantibodies binding 6 0 kDa has been studied extensively. Recent data have suggested that there a re disease-specific epitopes which identify patients with either SLE or SS. Alternatively, other data suggest that the B cell epitopes of 60 kDa Ro va ry according to the presence of anti-La. The present study was under-taken to determine whether binding of putative disease-specific 60 kDa Ro epitope s is associated with the diagnosis of SLE vs SS, or instead associated with the presence of anti-La. Anti-60 kDa Ro positive sera from 24 SLE patients and 44 SS patients were studied for antibodies binding two epitopes of 60 kDa Ro. We find the epitope defined by residues 171 - 190 is associated wit h anti-60 kDa Ro without anti-La, regardless of diagnosis. Meanwhile, bindi ng of the epitope defined by residues 215-232 is not commonly found in anti -60 kDa Ro sera, especially in those sera with both anti-60 kDa Ro and anti -La. Thus, the fine specificity of antibody binding to 60 kDa Ro varies acc ording to the presence of anti-La, not to the diagnosis of either SLE or SS .