Endogenous retroviruses and MS: using ERVs as disease markers.

Multiple sclerosis (MS) has an unknown cause, but its epidemiology suggests an interplay between environmental factors, possibly including viruses, and genetic components. Endogenous retroviruses (ERVs) are elements of the human genome that potentially may act as either genetic markers for polymorphisms related to MS, or markers of environmental/endogenous stress. Activation of the ERVs HERV-H/RGH, HERV-W and ERV-9 was reported when specific cell types (mainly B cells) from MS patients were cultivated in vitro. Viral RNA from these ERVs has been detected by reverse-transcriptase polymerase chain reaction in sera/plasma and brain tissues from MS patients, although not exclusively from these patients. ERVs play unknown roles in MS: their activation may represent an inflammatory cytokine-mediated epiphenomenon; alternatively, preliminary evidence suggests that specific ERVs may act as auto-, super- or neoantigens with the potential to enhance inflammatory responses or induce autoimmune reactions. ERVs that occur in few copies in the human genome (e.g. ERV-3 and human endogenous retrovirus, HRES-1) may show polymorphic patterns in MS. Studies show that the sequences encoding the envelope protein of ERV-3 are polymorphic to a degree where it becomes impossible to link them with MS. In contrast, the HRES-1 long terminal repeat sequence has a polymorphic pattern with haplotypes characteristic of MS. Haplotypes from non-MS control groups were identical between different topographic areas, but haplotypes from MS patients were different, depending on the population.