Immunochemical characteristics of antibodies to DNA in patients with active systemic lupus erythematosus.

To investigate the suggestion that qualitative immunochemical characteristics of antibodies to DNA (anti-DNA) may be of importance in the pathogenesis of nephritis in systemic lupus erythematosus (SLE), we used the Crithidia luciliae (CL) immunofluorescence test to determine the titre, immunoglobulin (Ig) class and complement-fixing activity of anti-DNA in thirty-five patients with active SLE. Eighteen of these patients had active lupus nephritis (Group I) and the remaining seventeen had no clinical evidence of renal involvement (Group II). Anti-DNA was detected in twenty-eight patients, and was present more frequently and in higher titre (P less than 0.01) in Group I than in Group II. Anti-DNA of all three Ig classes studied (IgG, IgM and IgA) was present in twenty-three out of twenty-eight cases. The ratio of IgG to IgM anti-DNA did not differ in the two groups of patients. Complement-fixing antibodies were detected in thirteen patients in Group I and five patients in Group II. The titre of complement-fixing activity was strongly correlated with titre of anti-DNA. DNA-binding capacity was also determined in these by a millipore filter (MF) assay. A highly significant correlation between DNA binding by MF and CL was found in Group I patients, while no correlation was found in Group II patients. These findings suggest that (1) anti-DNA with specificity for determinants found in CL, presumably native DNA, are more highly correlated with the presence of active renal lupus than are antibodies directed toward other DNA determinants, and (2) the major characteristic of anti-DNA found to be associated with nephritis was quantity of antibody. Most patients had anti-DNA of all Ig classes regardless of the presence of renal disease. Complement-fixing activity of anti-DNA could not be related to the occurrence of renal disease independently of anti-DNA titre.