Characterisation of nucleolar proteins as autoantigens using human autoimmune sera

Sera from 271 patients with systemic rheumatic diseases were screened for antinucleolar antibodies using immunofluorescence. Antinucleolar antibodies were found in the sera of 73% of patients with progressive systemic sclerosis, 4% of patients positive for autoantibodies with rheumatoid arthritis, and 8% of patients with rheumatoid arthritis associated with sicca complex, but not in patients with systemic lupus erythematosus, Sjögren's syndrome, undifferentiated connective tissue disease, or in healthy donors. The antinucleolar sera (n = 20) were analysed by immunoblotting techniques. In four sera antibodies against nucleolar proteins with molecular weights of 35 kD, 37 kD, 69 kD, 92-93 kD, and 93 kD could be immunodetected. The nucleolar autoantigens were extractable from the nucleoli together with the preribosomal particle fraction and could be solubilised by ribonuclease (RNAse) treatment. Their presence in the nucleolus was sensitive to actinomycin D treatment of cells. The 37 kD autoantigen could be identified as nucleolar phosphoprotein B23.