Isolation of DNA from DNA/anti-DNA antibody immune complexes in systemic lupus erythematosus.

A low molecular weight DNA fragment was isolated from DNA/anti-DNA antibody immune complexes found in patients with active systemic lupus erythematosus (SLE). Total sera were treated with 40% saturated ammonium sulfate to isolate gamma-globulin fraction and phenolized to partition proteins and nucleic acids. After being treated with RNAase, the sample was labeled at the 5' end with 32P-phosphate and electrophoresed in an 8% polyacrylamide gel, which was dried and autoradiographed. The sample that migrated at positions of molecular weight between 20,000 and 28,000 was susceptible to DNAase I but resistant to S1-nuclease. The data suggest that the immune complexes of SLE patients contain double-stranded DNA with 30 to 40 base pairs.