A new study suggests ancient viruses are involved in the acute inflammatory defense response that may contribute to multiple sclerosis. The study’s authors say that, in MS, activation of viruses is not linked to an infection. It is linked to the unexpected use of the body’s defensive responses, leading to chronic excessive inflammation. They said the discovery of this mechanism may one day pave the way for management of MS using small molecules that inhibit chromatin modification enzymes.

MS is an incurable inflammatory autoimmune disease that leads to irreversible damage to the brain and spinal cord. This disease is also associated with the reactivation of ancient viruses that were inserted in our DNA during the evolution of humankind. It was therefore long thought that MS was due to a viral infection.

Scientists at the Institut Pasteur, in Paris, said the study shows that reactivation of ancient viruses does not correspond to an infectious phenomenon, but to a defense response of the body when faced with an acute inflammatory phenomenon. Viral sequences were neutralized during evolution and no longer represent a source of infection. But these sequences are a source of external DNA containing information about virus behavior. Cells have therefore been able to control these sequences to detect infections as quickly as possible and turn on their defense genes during an attack.

These viral sequences are, above all, used to control defense genes in stem cells. They lie dormant in adult cells and it is the more traditional sequences that become active. By examining samples from patients with MS, the scientists observed that regulatory sequences of viral origin emerged from their dormant state and were responsible for abnormal expression of several proinflammatory genes.

The findings were published in the EMBO Journal.