Objective: To characterize DNA in sera of patients with systemic lupus erythematosus (SLE) in terms of size, guanine plus cytosine (G+C) content (by percentage), CpG dinucleotide (CpG) (percentage), and effects on mononuclear cells (MNC).
Methods: Nine DNA clones were sequenced. Oligodeoxynucleotides with the characteristic CpG motif (TTCGAA or PuPuCGPyPy) were examined for their proliferative effect on MNC by [3H]thymidine incorporation, expression of HLA-DR and intercellular adhesion molecule (ICAM)-1 on monocytes by flow cytometry, and mRNA levels encoding interleukin 12 (IL-12) and interferon-gamma (IFN-gamma) by semiquantitative reverse transcription polymerase chain reaction.
Results: The size of DNA clones ranged from 87 to 318 bp (mean +/- SD, 177+/-68) and enrichment in G+C and CpG ranged from 34.7 to 69.7% (48.1+/-10.7) and 0.63 to 12.8% (4.0+/-4.1), respectively. Three of 9 clones contained the characteristic CpG motif. Oligonucleotides proliferated MNC, and augmented HLA-DR and ICAM-1 expression in company with an increase of mRNA encoding IL-12 and IFN-gamma.
Conclusion: Circulating CpG motif-containing DNA fragments in SLE increased mRNA encoding IL-12 and IFN-gamma, which in turn increased HLA-DR and ICAM-1 on monocytes, resulting in MNC proliferation. This mechanism could contribute to the pathogenesis of SLE.