Back in my medical student days, when we could not figure out the cause of a disease, we’d more often than not blame a virus.

Well, now the prestigious Karolinska Institute in Stockholm has come up with evidence showing how the Epstein-Barr virus can trigger multiple sclerosis. Turns out some people make antibodies against the virus that mistakenly attack a protein in the brain and spinal cord, causing MS.

The EpsteinBarr virus (EBV) is very common and causes glandular fever, infecting most people early in life then remaining in the body, usually without symptoms. The link between EBV and multiple sclerosis (MS) has been known for many years, but only recently have we heard that EBV infection precedes MS and that antibodies against the virus may be involved.

“MS is an incredibly complex disease, but our study provides an important piece in the puzzle and could explain why some people develop the disease,” says Olivia Thomas of the Karolinska Institute and shared first author of the paper. “We have discovered that certain antibodies against the Epstein-Barr virus, which would normally fight the infection, can mistakenly target the brain and spinal cord causing damage.”

The researchers analysed blood samples from more than 700 patients with MS and 700 healthy individuals. They found antibodies that bind to a protein in the Epstein-Barr virus, EBNA1, can also bind to a similar protein in the brain and spinal cord called CRYAB, whose role is to prevent inflammation.

These misdirected, cross-reactive antibodies may damage the nervous system and cause severe symptoms in MS patients, including problems with balance, mobility and fatigue. The antibodies were present in about 23% of MS patients and 7% of control individuals.

“This shows that while these antibody responses aren’t required for disease development, they may be involved in disease in up to a quarter of MS patients,” says Olivia. “This also demonstrates high variation between patients, highlighting the need for personalised therapies. Current therapies are effective at reducing relapses in MS but none can prevent disease progression.”

Researchers also found there is likely to be a similar cross-reactivity among T cells of the immune system and MS. Mattias Bronge, also of Karolinska Institute, and shared first author, said: “We are now investigating how T cells fight EBV and how immune cells may damage the nervous system in MS and lead to disease progression.”