The incidence of antibodies to a soluble nuclear antigen in the sera of patients with systemic lupus erythematosus and rheumatoid arthritis estimated with the mixed haemadsorption technique.

The incidence of antibodies to a `soluble' nuclear antigen in sera from cases of connective tissue disease was studied with the mixed haemadsorption technique, which was more sensitive than the indirect immunofluorescent test and more accurate for quantitative determinations. The results with unabsorbed sera were not affected by the coexistence of antibodies to nucleoprotein and desoxyribonucleic acid (DNA). Antibodies to soluble nuclear antigen were four times more common in sera from cases of systemic lupus erythematosus (SLE) than in sera from cases of rheumatoid arthritis, where they were about as frequent as in sera from healthy male blood donors. However, their incidence in SLE was 50% and thus not high enough to make them useful as an independent diagnostic criterion. The antigenicity of the soluble nuclear material was preserved after treatment with acetone but not with ethanol.