A new study found that part of the Epstein-Barr virus mimics a protein made in the brain and spinal cord, leading the immune system to mistakenly attack the body’s nerve cells. This study shows how the common herpes virus can trigger MS by prompting the immune system to attack the nervous system.
Scientists have previously tried to pinpoint a link between specific viral infections and the onset of multiple sclerosis. However, they have been unable to prove such a link. MS is a crippling autoimmune disease that affects nearly 1 million Americans.
A new study led by Stanford Medicine researchers has changed that failure into success. The study showed that EBV can trigger MS. The study, published Jan. 24 in Nature, shows that approximately 20% to 25% of patients with multiple sclerosis have antibodies in their blood that bind tightly to both a protein from the Epstein-Barr virus, called EBNA1, and a protein made in the brain and spinal cord, called the glial cell adhesion molecule, or GlialCAM.
“Part of the EBV protein mimics your own host protein — in this case, GlialCAM, found in the insulating sheath on nerves,” said William Robinson, MD, Ph.D., professor of immunology and rheumatology at Stanford. “This means that when the immune system attacks EBV to clear the virus, it also ends up targeting GlialCAM in the myelin.”
When myelin is damaged, electrical impulses fail to jump efficiently between nerves, which can cause muscle weakness, numbness, and severe fatigue of MS.
The lead author of the study is Stanford research scientist Tobias Lanz, MD. The senior author is Robinson, the James. W. Raitt Professor, who credited co-author Lawrence Steinman, MD, professor of neurology at Stanford, with also playing a key role in driving the research.
“This is the first time anyone has shown rather definitively that a virus is a trigger for multiple sclerosis,” Steinman said. “And these exciting findings open up some new directions for clinical trials in MS treatment.”
MS and EBV
Past studies show that MS patients have a greater number of antibodies to an array of viruses including mumps, measles, EBV, and varicella-zoster. In fact, over 99% of MS patients have EBV antibodies in their blood. This is higher than the 94% of healthy individuals with EBV antibodies. However, researchers have had difficulty proving a causal connection.
“Nobody really knows what causes autoimmune diseases, and for many decades, all sorts of different viruses have been hypothesized,” Robinson said. “But when people did further mechanistic digging, everything fell apart, and it turned out that getting those other viruses didn’t actually cause MS.”
The Stanford Medicine team began by investigating the antibodies produced by immune cells in the blood and spinal fluid of nine MS patients. The immune cells of MS patients travel to the brain and spinal cord, where they produce large amounts of a few types of antibodies. Patterns of these antibody proteins, called oligoclonal bands, are found by analyzing the spinal fluid in the effort to diagnose MS.
“No one knows exactly what those antibodies bind to or where they’re from,” Robinson said. “So the first thing we did was analyze the antibodies from the oligoclonal bands, and showed that they come from B cells in the spinal fluid.”
The team has tried to sequence the B cells for about 8 years. “In the past, researchers would take serum and spinal fluid from MS patients and test them on planar arrays or throw them on histology slides to see what sticks,” Lanz said. “What we did was a different approach: We took B cells from the spinal fluid, single-cell sorted them and sequenced each one separately. In a single-cell format and at the scale of tens to hundreds of B cells per patient, that had not been done before.”
When the scientists found that the B cells in spinal fluid produced the oligoclonal bands in MS, they examined the specific antibodies and tested them for reactivity to multiple antigens.
“We started with human antigens,” Robinson said, “but couldn’t find clear reactivity. So eventually we tested them against EBV and other herpes viruses, and lo and behold, several of these antibodies, and one in particular, bound to EBV.”
67% of the patients in the study had antibodies that bound to the EBV protein EBNA1, while 89% had antibodies to some fragment of EBNA1. The researchers focused on one antibody that binds EBNA1 in a region known to elicit high reactivity in MS patients. Then they were able to determine which parts of the antibody-antigen complex was so crucial to binding.
In addition, the scientists found that the antibody bound with a high affinity to GlialCAM, leading them to conclude that they had discovered the specific mechanism by which an EBV infection may trigger MS.
“EBV tricks the immune system into responding not only to the virus, but also to this critical component of the cells that make up the white matter in our brains,” Steinman said. “To use a military metaphor, it’s like friendly fire: In fighting the virus, we damage our own army.”
The team also set out to determine how many cases of MS may be caused by this mechanism and found higher rates of reactivity to the EBNA1 protein and GlialCAM in 20% to 25% of blood samples in three separate MS cohorts.
“Twenty-five percent is a conservative number,” Robinson said, noting that it doesn’t include patients who may have previously reacted to GlialCAM following EBV infection but whose immune response has evolved since the initial trigger.
Mouse models offer additional evidence
In work guided by co-author and senior research scientist Peggy Ho, the importance of the anti-EBNA1 immune response was further assessed by using a common mouse model of MS called experimental autoimmune encephalomyelitis. After receiving an injection of a fragment of the EBNA1 protein, the mice exhibited more severe paralysis, more immune cells invading their central nervous system, and more damage to the protective coating on their nerve cells, compared with mice injected with a control protein fragment.
“It’s just further connecting the dots,” Robinson said. “If you immunize a mouse with a particular antigen and it makes paralysis worse, it suggests that an immune response against that target can contribute to MS pathogenesis.”
The future of MS treatments
This discovery may lead to new clinical treatments for MS. “If a virus is the target of the immune response that’s going an unwanted way in the MS brain, why not get rid of the virus?” Steinman said.
But this research also demonstrates why manufacturers would need to be extra careful in selecting which antigens to incorporate into an EBV vaccine. “You don’t want to choose those antigens, like EBNA1, that could cause autoimmunity,” Lanz said.
In addition, an EBV vaccine wouldn’t necessarily help patients who have already developed EBNA1/GlialCAM cross-reactivity. For those patients, a better option might be to induce the immune system into tolerating the GlialCAM, “There are two promising technologies here, one involving a reverse vaccine using DNA plasmids and another using RNA technology from the same company in Germany that made the Pfizer vaccine for COVID-19.”
The discovery of how EBV triggers multiple sclerosis may provide even lead to more effective treatments for other autoimmune diseases.