Researchers uncovered a new clue to how the Epstein-Barr virus may contribute to multiple sclerosis. A new study found certain types of CD8+ “killer” T cells are more abundant in people with MS. Some of these killer T cells target EBV, suggesting the virus may trigger the damaging immune response seen in MS.

MS, a chronic autoimmune disease that affects nearly one million Americans, develops when the immune system mistakenly attacks the myelin that coats nerve fibers in the brain and spinal cord, leading to progressive neurological damage. Scientists have known for several years that EBV — a common virus carried by about 95 percent of adults — is present in virtually everyone who develops MS.

Until now, most MS research has focused on CD4+ T cells, which coordinate immune responses but do not directly kill cells. CD4+ T cells are easier to study in animal models of MS than CD8+ killer T cells — immune cells that destroy damaged or infected cells.

A research team at University of California - San Francisco examined the killer T cells directly in people. They analyzed blood and cerebrospinal fluid from 13 patients with MS or early signs of the disease, as well as five people without MS. The researchers looked at CD8+ T cells that recognized specific proteins in each of these fluids. 

In the study, in the participants without MS, the cells that recognized these proteins were similarly abundant in the blood and CSF. But in the participants with MS, these cells were between 10 and 100 times more abundant in the CSF than in the blood. This huge difference indicated something unusual must be happening in the central nervous system — and that the immune cells were responding to it. 

The Epstein-Barr virus was also present in the CSF of most study participants, whether or not they had MS, and some of its genes were active. One of these genes was only active in people with MS, which suggests that it may be driving the overactive immune response characteristic of MS.

The findings are just the latest to implicate EBV in autoimmune disease. Some MS researchers have already begun testing therapies that target EBV. 

The findings were published in the journal Nature Immunology.