Immunosorbent Assay for Quantitation of Antibody

Antibodies to the Ro/SSA antigen occur in patients with systemic lupus erythematosus and Sjogren's syndrome. An immunoaffinity method for the preparation of electrophoretically homogeneous Ro/SSA antigen is described. Several molecular properties of the antigen have been determined. The native RNA protein particle has a molecular weight of 100,000 D determined by gel filtration. Sodium dodecyl sulfate-analysis of the purified Ro/SSA antigen and analysis by staining ofbands with silver and Coomassie Blue, Western blotting, and RNAase treatment leads to a hypothesis for the structure of the particle in which an antigenic 60,000 protein is bound to 24,000-27,000 RNA molecules which are not antigenic. An enzyme-linked immunoabsorbent assay method for assay of anti-Ro/SSA is also described which sensitively measures antigen binding at dilutions of sera containing anti-Ro/SSA precipitins up to I07 fold. Normal sera on average have 103 less binding activity.