IgG antibodies to double-stranded DNA in systemic lupus erythematosus sera. Independent variation of complement fixing activity and total antibody content.

Antibodies to double-stranded deoxyribonucleic acid were studied using the kinetoplast of Crithidia luciliae. Titers were determined separately by conventional immunofluorescence and the complement fluorescent technique, and results by the two methods were compared. Complement fixing activity varied independently of antibody content in whole serum and in IgG fractions. The well established correlation of complement fixing activity of this antibody with activity of lupus nephritis appears related, therefore, to qualitative rather than solely quantitative differences. This finding has important implications for the clinical assessment of patients with lupus, and investigations on the relationship of anti-DNA antibodies to lupus nephritis.