Can this virus really cause MS?
Paper #1: Longitudinal analysis reveals high prevalence of
Epstein-Barr virus associated with multiple sclerosis
Kjetil Bjornevik, Marianna Cortese, Brian C. Healy et al
Science 375, 296–301 (2022) 21 January 2022
Paper #2: Clonally Expanded B Cells in Multiple Sclerosis
Bind EBV EBNA1 and GlialCAM
Tobias V. Lanz, R. Camille Brewer, Peggy P. Ho et al
Nature (2022), Published Online, https://doi.org/10.1038/s41586-022-04432-7
Paper #1: The authors of this paper asked the question: “Could a virus that affects more than 90% of adults possibly be a cause of MS?” They addressed this question using blood samples collected from all persons at the time of entering the US Military and periodically thereafter. Millions of samples are stored. This landmark study examined serum samples from 801 individuals who developed MS after entering US military service. All but one had antibodies to Epstein-Barr virus at the time of MS diagnosis. A subgroup of thirty-five individuals who subsequently developed MS had no Epstein-Barr virus antibodies at the time of entry into the US military. These individuals were compared to 107 persons who also were EBV antibody negative but did not develop MS. Ninety-seven percent of individuals (34 out of 35) who subsequently developed MS developed antibodies to EBV at a median time of 5 years before being diagnosed. Only 57% of controls developed EBV antibodies. The authors calculated that infection with EBV increased the risk of developing MS 32-fold. Results were specific for Epstein-Barr virus in that infection with another common virus, cytomegalovirus (CMV), was no different in persons with MS and controls. The researchers also measured levels of serum neurofilament light chains (sNfL), a marker of tissue damage, in both groups (see my blog from October 5, 2019). In the MS group levels of sNfL were normal prior to infection with EBV but increased following infection, years before the diagnosis of MS. No changes were seen in the control group. The authors suggest that a vaccine to prevent Epstein-Barr virus infection may not only be a potential treatment for established MS but might be able to prevent the disease in susceptible individuals.
Paper #2: This paper provides evidence for how infection with Epstein-Barr virus could lead to MS. The authors studied immune cells called B-cells from the spinal fluids of persons with MS. B-cells make antibodies and cerebrospinal fluids (CSF) of persons with MS contain unique antibodies not found in blood. The authors showed that there were clones of B cells in the CSF of persons with MS and that these B cells made antibodies that bound to both a protein of the Epstein-Barr virus (EBNA1) and to a brain protein, glialCAM, found on cells called astrocytes and oligodendrocytes. While antibodies to the particular EBV protein (EBNA1) were found both in persons with MS and controls, only persons with MS had antibodies that also bound to glialCAM. Immunizing mice with EBNA1 made subsequent development of the MS-like disease experimental autoimmune encephalomyelitis, worse. The authors concluded that, while infection with EBV results in immune responses to the virus in both persons with MS and controls, in persons with MS the infection results in an immune response that is different than seen in controls, one that reacts to EBNA1, but also cross-reacts with glialCAM on oligodendrocytes, the myelin producing cells, resulting in brain inflammation.
Key Points Related to the Featured Papers:
1. More than 90% of adults are infected with Epstein-Barr virus (EBV) and have antibodies to the virus. In most individuals the virus does not cause illness, but EBV can cause infectious mononucleosis and even malignancies of blood and other tissues.
2. EBV has long been suspected as playing a role in MS but demonstrating that such a common infection is needed for the development of this illness and understanding how such infection results in central nervous system inflammation was not known.
3. The authors of Paper #1, using the invaluable collection of blood samples of the US military, were able to identify 35 individuals who entered the military, had not been infected with EBV and thus were antibody negative, and subsequently were diagnosed with MS.
4. By studying pre- and post-diagnosis blood samples from these individuals, the authors were able to show that 34 of the 35 these individuals became infected with EBV about five years prior to the diagnosis of MS, and that with infection there was evidence of central nervous system damage, shown by the appearance of elevated levels of neurofilament light chains (sNfL) , a protein released from injured nerve cells.
5. The authors looked for other viruses, such as cytomegalovirus (CMV) that could have explained this. None were found. Indeed, infection with CMV may have had a protective effect.
6. There was no evidence of “secondary causation”, such as MS resulting in impaired immune responses to Epstein-Barr virus, thus increasing the risk of becoming infected. No other known “confounding” factors could explain the association between becoming infected with EBV and developing MS.
7. These observations establish for the first time that in susceptible individuals infection with EBV is associated with the appearance of central nervous system injury, and a greatly increased risk of developing MS.
8. While infection with EBV appears necessary for the development of MS, infection alone is not sufficient. What must now be determined are the susceptibility factors that result in this common viral infection triggering this relatively uncommon disease.
9. Paper #2 asked the question: “How can an immune response to Epstein-Barr virus trigger an immune reaction in the central nervous system?”
10. First, a fact: antibodies are increased in the spinal fluids of persons with MS, with certain antibodies (oligoclonal bands) found only in spinal fluid and not in blood.
11.The authors of Paper #2 studied immune cells from spinal fluids of persons with MS. In particular they studied B-cells, the cells that make antibodies.
12.They discovered several things. First, they found that MS spinal fluid B-cells were clonally expanded, meaning that the cells were not randomly increased in number but were reacting to a particular stimulant or antigen.
13.Second, using these B-cells they were able to produce a monoclonal antibody that bound to a particular EBV protein, one that had been implicated in the development of MS (EBNA1).
14.This antibody was then tested against a large panel of different central nervous system proteins to see if any cross-reacted with the antibody. They found one such protein, called “glialCAM.”
15.This protein is found on two cell types in the central nervous system, astrocytes and oligodendrocytes, the latter being the cells that make myelin.
16.The authors found that both EBNA1 and glialCAM shared a very similar amino acid sequence, and that this was the area that the antibody bound to. They also noted that while both persons with MS and controls had antibodies in their blood to EBNA1, many more persons with MS had antibodies that also bound to glialCAM. Thus, the pattern of immune response to the Epstein-Barr virus was different in persons with MS compared to controls. The same phenomenon was noted when blood cells from persons with MS and controls were stimulated with EBNA1 and glialCAM. While some immune cells (CD4+ T cells) in both groups responded to stimulation with both proteins, only CD8+ T cells from persons with MS responded to glialCAM.
17.The authors then studied an MS-like disease in mice called “experimental autoimmune encephalomyelitis,” or EAE. They noted that if mice were first immunized with the viral protein EBNA1 and then induced to have EAE, the disease was much worse. Antibodies to EBNA1 in mice also reacted with glialCAM and bound to central nervous system tissues. These data provided additional support for the observation in humans that immune responses to the viral protein EBNA1 can cross-react with particular central nervous system proteins and worsen an inflammatory central nervous system disease.
18.The above observations, in addition to those noted in Paper #1, support the hypothesis that infection with Epstein-Barr virus in susceptible individuals results in a pattern of immune response that cross-reacts with particular central nervous system proteins such as glialCAM, causing tissue damage and initiating an inflammatory reaction that greatly increases the risk for MS. The discussion below reviews some of the implications of these findings.
Viral infections are known to trigger a variety of autoimmune processes. Most recently SARS-CoV-2 infection was shown to cause autoimmune reactions. As noted above, there is a strong association between infection with Epstein-Barr virus (EBV) and MS. The exact mechanisms defining how this happens remain poorly understood, but the two featured papers provide strong evidence that infection with EBV greatly increases the risk of developing MS, via a pathway in which susceptible individuals make a pattern of immune response that cross-reacts with central nervous system tissues, in particular with oligodendrocytes, the cells that make myelin. These observations suggest that preventing infection with EBV may have therapeutic benefit, both for persons with MS and those at risk for developing the illness.
There are, however, several potential caveats with this approach. The first is that we don’t know which EBV proteins or messenger RNAs to use to produce such a vaccine. Second, we don’t know the susceptibility factors involved in making persons vulnerable to the autoimmune effects of EBV infection. It is conceivable that immunization with EBV proteins in susceptible individuals could trigger MS. An alternative approach may be to induce immune tolerance to EBV, that is a state in which an MS-susceptible individual’s immune system does not respond to the virus. However, this may allow the virus to multiple unfettered, an equally unsatisfactory outcome. Finally, as expected with an illness as heterogenous as MS, not all persons with MS had cross-reactive anti-glialCAM antibodies. Thus, there almost certainly are additional pathways for triggering MS.
To summarize, the two featured papers provide strong evidence that infection with EBV in susceptible individuals greatly increases the risk of developing MS, and that this may occur due to a unique pattern of immune response to the virus that cross-reacts with a central nervous system protein. Much more work still needs to be done defining those factors that make persons susceptible to MS, and how to alter the immune response to EBV without triggering brain damage.