Background: In recent years, it has been suggested that human endogenous retroviruses (HERVs) may play a role in autoimmune diseases. HERVs represent both putative susceptibility genes and putative pathogenic viruses in multiple sclerosis (MS). Initially, our objective was to characterize a retrovirus produced by MS derived cell lines and to investigate this association in vivo.

Methods: The retrovirus was identified by RT-PCR on virion RNA purified from RT-positive retroviral particles from the MS cell lines, and from blood samples from MS patients. Wistar rats were immunized with purified virions and serological responses analyzed by ELISA.

Results: Sequence variants highly homologous to the HERV-H family were found. The same sequences were specifically found in the particulate fraction of a series of MS patient plasma samples and were absent in controls. A database search demonstrated HERV-H copies in several chromosome regions implied in MS susceptibility. Virion-immunized rats developed a specific serological response towards HERV-H peptides indicating that immunogenic virion proteins are encoded by HERV-H.

Conclusions: Activation of normally replicatively quiescent HERVs may be causally involved in MS.