Qualitative characteristics of anti‐DNA antibodies in lupus nephritis

Sera from 38 patients with systemic lupus erythematosus, known from previous determinations to contain antibodies to native DNA (deoxyribonucleic acid), were studied using a modification of the Farr technique, with 14 C‐DNA as ligand. The sera fell into three groups with regard to antibodies to DNA: a) precipitating, b) nonprecipitating, and c) a mixture of both. Eighteen of these sera were studied further and titrated to obtain measures of their antigen binding capacity and estimates of avidity for DNA. Patients with lupus nephritis had either precipitating antibodies to DNA, or a mixture of precipitating and nonprecipitating, whereas those patients without nephritis had only nonprecipitating, antibodies to DNA. Furthermore the avidity for DNA was greatest in sera from patients with nephritis. The antigen binding capacity of sera from patients with and without lupus nephritis was similar, suggesting that qualitative differences in anti‐DNA activity may be as important as quantitative ones.