Association between the Ro and La antigenic determinants: immunodiffusion analysis of human spleen extract

The Ro (SS-A) and La (SS-B) antigenic determinants appear to be related to one another because of the frequent coincidence of spontaneous anti-Ro and anti-La in the same autoimmune sera, and because of a tendency of the Ro and La immunoprecipitin lines in double immunodiffusion analysis to fuse. We have developed an enzyme immunodiffusion staining (EIS) procedure that permitted us to identify the specific antigenic determinants found in an immunoprecipitin line. By using this technique with human spleen extract, we showed that the Ro and La particles are found together as a complex, as well as individually. The EIS technique insured that our results were not confounded by lack of monospecificity of our autoantibody and antigenic reagents. Ro-La antigenic complexes exist at physiologic pH, and are dissociated by high ionic strength. They may be formed in vivo either intracellularly or extracellularly. Such Ro-La complexes could be immunogenic, and thereby might account for the frequent coincidence of the anti-La and anti-Ro autoantibody specificities.