Autoantibodies against RNA polymerase I in scleroderma and Sjögren's syndrome sera

Anti-RNA polymerase I antibodies were detected by radioimmunoassay in the sera of 8 out of 9 Sjögren's syndrome patients, 11 out of 19 individuals with scleroderma, and 19 out of 19 systemic lupus erythematosus patients. The results of the radioimmunoassay were confirmed by demonstrating the ability of the patients' IgG to inhibit RNA polymerase I activity in vitro. Sera from four patients in each category were also tested for reaction with individual subunits of RNA polymerase I. All 4 SLE sera, 3 out of 4 scleroderma sera and 1 out of 4 Sjögren's syndrome sera contained antibodies against the 65 kDa (S3) subunit of RNA polymerase I in addition to antibodies against one other subunit. Sera from the remaining scleroderma and Sjögren's syndrome patients tested in this assay contained only anti-S3 antibodies. These results demonstrate that anti-RNA polymerase I antibodies are characteristic of a variety of rheumatic autoimmune sera.