Antibodies to extractable nuclear antigens in rheumatoid arthritis: relationship to vasculitis and circulating immune complexes.

Antibodies to extractable nuclear antigens (ENA) were analysed in the sera of fifty-two patients with severe rheumatoid arthritis (RA) who were divided into two categories: twenty-five with arthritis only and twenty-seven with extra-articular disease. Using haemagglutination, counterimmunoelectropheresis (CIE) and double diffusion, antibodies to ENA were detected in three (12%) of the patients with arthritis only. In the group with extra-articular disease, antibodies were found in sixteen (59%) of the patients. In ten patients the antibodies reacted with an RNase and DNAse resistant, but trypsin sensitive protein component of ENA. These patients all had extraarticular disease with digital vasculitis being a particularly common feature. Their sera also contained circulating immune complexes detected by elevated cryoprecipitate protein levels associated with relatively low complement levels. It is suggested that antibodies to soluble proteins of nuclear origin may be markers of circulating immune complexes in extra-articular RA.