Are retroviruses involved in the pathogenesis of SLE?

Summary

High molecular weight DNA of up to 20 kbp and, additionally, an RNase-insensitive RNA of more than 60 b were isolated from plasmapheresis fluids taken from patients with active systemic lupus erythematosus (SLE). Similar nucleic acids could not be demonstrated in the plasma samples from patients with Waldenstroem's disease, rheumatoid arthritis, myasthenia gravis, and other diseases including active systemic disorders. The purified nucleic acids were analyzed in several ways; they proved to be immunogenic by inducing polyclonal and monoclonal antibodies to natural DNA as well as to synthetic polynucleotides (e.g. polyguanylic acid) after injection into experimental animals (rabbits or mice respectively). Biochemical and molecular cloning analysis of the DNA revealed features like high levels of CpG-dinucleotides, usually not observed in common human DNA. A possible exogenous origin was substantiated by comparative sequence studies of cloned plasma DNA, which showed homologies to human retroviruses, e.g. PL1 (85%/60 b) and the sequences of the gag and pol genes of human immunodeficiency virus type I (85%/157 b). Experiments applying isolated plasma nucleic acids in transfection experiments showed the induction of morphological changes in an EBV-immortalized B-cell line drawn from a healthy human donor, such as vacuolization and syncitia formation. Northern blot analysis demonstrated, exclusively in the transfected cell line, the expression of mRNA homologous to the cloned plasma DNA. Using this clone as a probe, homologous sequences could be demonstrated by Northern blot analysis in EBV-immortalized cell lines from SLE patients only and, by means of DNA amplification, in peripheral blood lymphocytes from SLE and AIDS patients. A cDNA library has been established, and sequencing is under way to gain more specific primers and probes for different chronic inflammatory diseases.