Antibodies to native and denatured deoxyribonucleic acid in systemic lupus erythematosus

The relative reactivities with native and denatured DNA of 35 lupus sera were investigated by quantitative complement fixation and precipitin studies and showed great variations. The use of purified native DNA demonstrated that, in at least 22 of these 35 sera, the anti-DNA antibodies reacted with the native form, independently of denatured contaminants. Systemic lupus sera were shown to contain three main types of DNA antibodies: those reacting only with denatured DNA, those reacting to the same extent with both forms of DNA, and those reacting preferentially with native DNA. In some instances, the latter antibodies fix complement and precipitate only with native DNA but are inhibited by the denatured form. This finding points to the importance of conformation in the antigenic structure of DNA. The simultaneous occurrence of different varieties of DNA antibodies was demonstrated in several sera. Evidence was obtained that some of these human antibodies to DNA can belong to the IgM class. Thus, DNA antibodies from systemic lupus patients differ in many respects from most of the experimentally produced antibodies capable of reacting with DNA.