Idiotypes on antibodies to the La (SS-B) antigen are restricted and associated with the antigen binding site.

Rabbit anti-idiotypic antibodies were prepared against affinity purified autoantibodies to the ribonucleoprotein La (SS-B) antigen from the sera of three unrelated patients. Each anti-idiotype recognized private idiotypes expressed only on the immunizing anti-La antibody. In each case they were conformationally dependent and related to the antigen binding site. This demonstration of immunodominant private idiotypes on human autoantibodies to ribonucleoproteins is in direct contrast to the cross-reactive idiotypes described on rheumatoid factors and autoantibodies to DNA. We discuss the possibility that anti-La antibodies, unlike anti-DNA, arise as a result of autoantigenic stimulation.