Antibodies to ribosomal ribonucleoprotein. Prevalence in systemic rheumatic diseases and partial characterization of the antigen.

The prevalence of antibodies to ribosomal ribonucleoproteins (rRNP) was studied in patients with rheumatic diseases. Seven patients had precipitating antibodies against rRNP, 6 had systemic lupus erythematosus, one had primary Sjögren's syndrome. Anti-rRNP was not present in mixed connective tissue disease, rheumatoid arthritis, progressive systemic sclerosis, CREST, primary Raynaud's or normal control sera. A partial immunological identity precipitin line was present between (U1) nRNP and rRNP, but these were distinct in physicochemical properties. Western blot analysis of ribosomal extract using anti-rRNP IgG revealed 2 polypeptides called rA and rB which appear to be the important antigenic determinants.