The incidence and clinical significance of antibodies to extractable nuclear antigens.

Sera from 378 patients were assayed for antibodies to extractable nuclear antigens (ENA), ribonucleoprotein (RNP) and nonnucleoprotein (Sm). Anti-ENA antibodies were not found in control subjects, patients with rheumatic diseases and negative fluorescent antinuclear antibodies (FANA), or in patients with rheumatoid arthritis, dermatomyositis, drug-induced lupus, idiopathic thrombocytopenic purpura (ITP), or hemolytic anemia with positive FANA. Anti-Sm antibodies were found in 32 per cent of patients with systemic lupus erythematosus (SLE) and were not found in any other condition. There were no significant clinical or serological differences between patients with and without anti-Sm antibodies. Anti-RNP antibodies occurred in 15 per cent of SLE patients, 9 per cent of scleroderma patients, and in 100 per cent of patients with mixed connective tissue disease. SLE patients with anti-RNP antibodies had a significantly lower anti-DNA antibody titer and a significantly lower incidence of nephritis and impaired renal function. Anti-Sm and anti-RNP titers did not vary with changes in clinical status. Awareness of the presence of anti-Sm and anti-RNP antibodies is diagnostically useful. Anti-RNP antibodies have a prognostic value as well.