Are Viral Infections Involved in Causing MS?

It is generally accepted that multiple sclerosis is an autoimmune disease, that is, a disease that arises from the body’s own immune system attacking and destroying the myelin sheath that surrounds nerves. However, what causes this attack of self is still unknown. One theory is called molecular mimicry. Essentially, this suggests that cells of the immune system that recognise parts of a virus or bacteria (as they are designed to do to help prevent and clear infections) can also recognise parts of the myelin sheath due to a small region of similarity between the two. It has been shown previously that parts of the Epstein-Barr virus (EBV – causes glandular fever) and human cytomegalovirus (HCMV) are very similar to parts of two of the major proteins that make up myelin (myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG)).A new study by Zheng et al has shown the potential for T cells (specialised cells of the immune system) specific to HCMV to cross-react with MOG and vice versa. When the experiment was extended to a mouse model of MS, however, the results were less significant. Nevertheless, this data provides some more evidence that may suggest previous infection with certain viruses may play a role in the development of MS. Further work is needed in this area to provide a conclusive answer.