Characterization of DNA in polyethylene glycol precipitated immune complexes from sera of patients with systemic lupus erythematosus.

The nature and the quantity of DNA present in the circulating immune complexes (ICs) from 30 patients with systemic lupus erythematosus (SLE) was characterized. DNA was extracted from IC enriched material prepared by polyethylene glycol precipitation of serum and the extracted DNA was labelled with 32P-phosphate. The size and the nature of DNA was determined by polyacrylamide gel electrophoresis and autoradiography. The quantity of DNA in the PEG precipitates from sera of 10 clinically active SLE was found to be significantly higher (mean 159 X 10(4) ct/min, range 49.9-807 X 10(4) ct/min) than 10 normal controls (mean 24.7 X 10(4) ct/min, range 8.7-47.8 X 10(4) ct/min). Four different sizes of DNA fragments were detected: 370-470, 150-240, 30-40 and 20 base pairs (bp). DNA of 30-40 bp and 20 bp were frequently present in both SLE and normals, but the other two large sized DNA fragments were particularly prominent in SLE patients. In the majority of samples, DNA fragments appeared double stranded.