This post ran a bit long, so a large nutshell is needed, maybe a coconut or better yet, Mr. Peanut himself. It’s becoming pretty evident Epstein-Barr Virus (EBV) infection is the underlying driver of MS. In my opinion, low vitamin D levels from womb through adolescence, EBV infection, HLA-DR15 haplotype, and citrullination of myelin proteins mostly cause MS.
It’s a bit to cover and I’m going to cherry-pick a bit from these topics. There’s references at the end if you’d like to go more in depth. Other factors are also likely involved, like human endogenous retroviruses, hormone receptors, sodium tissue levels, aberrant methylation, gut biome, numerous other MS risk genes and variants, etc. and so on, but I think these are key.
Vitamin D (VitD) is synthesized by the skin when it is exposed to UVB radiation (sunlight) that transforms cholesterol derivative (7-dehydrocholcholesterol) into vitamin D3 (cholecalciferol). Vitamin D3 then goes to the liver and is converted to 25-hydroxyvitamin D3 (calcidiol) by the CYP2R1 enzyme. This goes to the kidneys, where it’s converted to the active form, 1,25-dihydroxyvitamin D3 (calcitriol), by the CYP27B1 enzyme.
Calcitriol is vital for calcium homeostasis, but more importantly for MS, it interacts with the vitamin D receptor (VDR) in cells throughout the body that influence cellular immune system functions. Calcitriol binds to its transporter, Vit D-binding protein (VDBP), that controls it’s availability to cells. Calcitriol binds to the VDR that make a complex with RXR. The Vit D/VDR/RXR complex binds to the Vit D receptor element (VDRE) on DNA and regulates the expression of around 500 genes. VDREs are regulated by VitD and are in the promotor region of more than 80% of MS-associated genes. Therefore, low VitD levels can alter the expression of MS risk genes. VitD regulates immune cell epigenetic programming, promotes immunological T cell tolerance, and reduces the inflammatory response, all involved in MS pathogenesis. Polymorphisms in VDR, VDBP, CYP2R1, or CYP7B1 can all strongly affect VitD levels. Studies find active VitD levels are lower in MS and SPMS patients than in healthy controls, but others find no differences. High active VitD serum levels also associate with a significantly reduced risk of developing MS, but just in Caucasians and particularly in those under age 20. MS patients may benefit from supplementing VitD if they are deficient, but the greatest impact seems to be preventive, prior to MS development.
A report shows VitD is already needed in utero for negative selection of T cells. In T cell development, precursor T cells are selected by producing strong reactions against foreign antigens. These then go through the ‘negative selection’ process to eliminate T cells that react to body tissue. This develops ‘T cell tolerance’ and all T cells created in a lifetime are completed by puberty. Mice that can’t produce biologically active VitD have reduced T cell tolerance with strong responses to self-antigens. I go from white to pink in sunlight, so I likely had some, at least transiently, low VitD levels growing up.
The Epstein Barr virus (EBV) infects around 90-95% of people in the world and, as a herpesvirus, takes up lifelong residency in the body. In developing countries, kids usually get asymptomatic primary EBV infection in early life. In developed countries this can occur after age 10 when negative selection of T cells decreases and Th1 responses (inflammatory) increase. It can also cause infectious mononucleosis at this age which causes a huge T- cell response and increases MS risk 2-3 times. However, EBV can still cause neurological diseases even without acute infection.
EBV infects naïve B cells in the body to establish latency by expressing viral proteins to make them proliferate, transform, and differentiate into EBV-infected memory B cells (MBCs). The host cell expresses EBV gene products like nuclear proteins (EBNA-1/2/3A/3B/3C/LP), membrane proteins (LMP-1/2A/2B), and EBV-encoded small RNAs (EBER-1 and EBER-2) after EBV infection. These can control most of the the host’s B cell functions like the cell cycle and apoptosis. Once EBV enters the latent (dormant) phase it can more easily elude EBV-specific CD8+ T-cells.
Low vitamin D levels are associated with low levels of CD4+ and CD8+ T cells, which directly kill EBV-infected B cells. The ability of EBV-specific CD8+ T cells to proliferate and kill EBV-infected B cells in primary infection determines the EBV viral load ‘set point’ that will maintain throughout the host’s lifetime. The virus reactivates periodically to induce the lytic (active) phase of the disease which produces new virus particles (virions) that infect new naive B cells to keep levels at this set point. EBV latency in transformed B cells from MS patients is shown to be unstable and cells enter the lytic cycle more frequently. A chronic latent infection like this with sudden spikes of viral reactivation in the CNS can explain the persistent B cell activation, lesion reactivation (relapses), and predominant cytotoxic CD8+ T cells.
The role of EBV infection in MS pathogenesis can be seen by how over‐represented EBV nuclear antigen 2 (EBNA2) is at MS risk binding sites. EBNA2 drives EBV-B cell immortalization in primary infection, and has overlapping DNA binding sites with the VDR. It’s likely with high VitD levels, the VDR outcompetes EBNA2 for DNA binding, which can explain the inverse correlation seen between VitD levels and EBV.
EBV has some pretty clever tricks it uses to keep its viral genome hidden safely away in long-lived latent MBCs. It creates a mimic of the co-stimulatory molecule CD40 that can increase EBV-infected B-cell antigen presentation, reduce regulatory Treg cell activity, and inhibit the lytic phase. Inhibiting induction of the lytic phase maintains viral latency, and decreasing Treg cell activity exaggerates subsequent pro-inflammatory Th1 responses. Increasing antigen processing allows for cross-presentation between EBV and myelin antigens to cytotoxic CD8+ T cells.
EBV can also control anti-inflammatory cytokine IL-10, and creates a mimic of it. They work in tandem to regulate EBV load set points by enhancing EBV-infected naive B cell differentiation, proliferation, and survival. It also lets it regulate antiviral T cell activity, like by downregulating peptide transport into the endoplasmic reticulum. This reduces surface major history compatibility complex I (MHC-I) molecule expression and EBV antigens from being presented to EBV-specific CD8+ T cells.
Autophagy is a cellular process that eliminates defective or superfluous proteins, complexes, and organelles, to prevent accumulated cytotoxic damage. EBV-infected B-cells induce autophagy to use for survival, development, and activation. EBV-infected B cells can internalize and present citrullinated myelin basic protein (MBP) to autoreactive T cells, a process that is not seen in uninfected B cells. This is due to EBV-induced changes in how infected B cells process antigens.
MBP has a post-translational modification (PTM) where arginine residues in the protein are converted to citrulline in a process called deimination (citrullination). This changes the electrostatic charge of the protein and is irreversible. MBP citrullination is carried out in the cytoplasm by peptidyl–arginine deiminase 2 (PAD2). This results in the eight MBP charge isomers, C1–C8, with C1 not citrullinated with the highest charge (+19) and C8 the most citrullinated with the lowest charge. C8 makes up 100% of MBP in the first years of life, then switches over to an 80/20% ratio between 3-5 years of age to maintain compact myelin integrity. This allow areas for cytoplasmic channels to run between the oligodendrocyte and axon segment. MBP is the most studied myelin protein, but this process also occurs in other myelin proteins.
In think some EBV-infected MBCs follow the circulation and end up in the CNS. One of these comes across citrullinated MBP fragments in the extracellular CNS environment and captures it through their B cell receptor. EBV can control autophagy in latency and reactivation with its viral proteins. In EBV-infected MBCs, autophagy forms autophagosomes that sequester cytoplasmic components, including the citrullinated MBP. Autophagosomes fuse with lysosomes that contain the degrading enzymes. The citrullinated MBP is degraded into smaller peptides, but escapes complete degradation due to EBV-induced selective autophagy that inhibits the last phase (degradation). These peptides are loaded onto MHC class II molecules that are transported to the EBV-infected MBC cell surface which travels to the cervical lymph nodes and presents them to CD4+ T cells. EBV-infected B-cells are also seen to contain increased autophagosomes.
Oligodendrocyte precursor cells (OPCs) also have high levels of C8 MBP (in developmental myelin) that converts into C1 MBP when they differentiate and mature into oligodendrocytes (OLs). This is likely why high C8 MBP levels are seen in post mortem MS tissue samples due to attempted remyelination and accumulated OPCs in lesions that don’t mature into OLs.
Dysregulated PTMs are increasingly being seen as a cause of autoimmune disease pathogenesis. The neoepitopes are “new” to the immune system, and not impacted by tolerance mechanisms that prevent attacks on self-antigens. Their unique nature allows them to be readily recognized by the immune system as foreign, which enhances their ability to elicit an immune response (immunogenicity). They also have stronger MHC affinity, making them even more immunogenic. HLA allelles associated with greatest genetic MS risk (HLA-DRB1*15:01 and HLA-DRB5*01:01) preferentially present citrullinated peptides at particular HLA-binding sites.
The variety of methods EBV can use to manipulate the immune system shows how a higher viral load can detrimentally effect it’s functioning. This in turn leads to diseases in the body like MS, rheumatoid arthritis, lupus, diabetes, etc. Other herpesvirus are implicated in different types of autoimmune diseases. Vitamin D is a key defender against viruses in the body and its deficiency allows viruses to have increased effects. It’s ironic that the cause of MS is from T cells not being able to induce enough damage to EBV-infected B cells when they are responsible for all the damage caused in MS. The molecular mimicry between EBV and myelin components that occurs later doesn’t induce as strong a response as an antigen like MBP. This is why I think something like what I propose causes the large peripheral adaptive immune response that results in an initial MS attack.
HLA haplotypes are sets of human leukocyte antigen (HLA) “genes” (loci-alleles) by chromosome, one passed from the mother and one from the father. They are involved in how the body recognizes foreign antigens. The HLA locus is one of the highest disease-associated genetic loci in autoimmunity. The same HLA allele can be both protective and pathogenic for different autoimmune diseases. The alleles of HLA-DR15 (HLA-DRB1*15:01 and HLA-DRB5*01:01), increase the risk of developing MS, but protects against developing Type 1 diabetes. Changes in HLA alleles can predispose to or protect from autoimmunity by influencing the peptides presented on them, which shapes the adaptive immune response. The different HLA alleles have distinct peptide-binding preferences, which create unique peptides presented on the cell surface. The ability of MHC molecules to process and present epitopes from self and foreign proteins is critical for adaptive immunity. MHC also has high degrees of polymorphism, with thousands of class I (HLA-A, HLA-B, HLA-C) and class II (HLA-DP, HLA-DQ, HLA-DR) alleles. This diversifies T cell responses to pathogens at population levels, but makes it hard to find the peptides they present.
The HLA-DR15 haplotype is the strongest genetic risk factor for MS. Patients carrying it see increased MS susceptibility, along with HLA-B*07 and HLA-A*0301. The HLA-DR15 haplotype has two allelles, HLA-DRB5*01:01 (DR2A) and HLA-DRB1-15 *01 (DR2B) that are high on B cells. The allele is unique because these two molecules present different sets of peptides to the T cell. They also use residues from each other as self peptides that make up to half of the peptides they present using B cells. The peptides on the DR2A stem come from the DR2B chain and peptides on the DR2B stem are from the DR2A chain. They can act as antigen structures and epitope sources at the same time. Having these two allomorphs may explain its genetic association with MS by serving as a source of peptides that cross-react with encephalitogenic antigens. The MHC-II MBP peptide complex is presented by DR2b and the EBV peptide complex is presented by DR2a. The HLA-DRB1-15*01 also acts as a co-receptor for EBV infection on MHC-II. EBV specifically binds to the DR2B chain involved in forming the peptide binding groove. This allows the virus to more efficiently infect the host for a higher viral load.
The HLA-B*07 allele affects EBV DNA viral load the most. It is in the same HLA haplotype carrying the HLA-DRB1*15 allele. B*07 (HLA-B*07+) along with risk allele DRB1*15:01 and absent protective allele A*02 have the highest EBV viral loads. Increased viral loads seen in MS may be partly due to poor control of EBV reactivation by HLA-B*07+ restricted CD8+ T cells. HLA-B*07 antigen weakly presents viral epitopes to cytotoxic T cells.
T cells mediate autoimmune disorder pathogenesis by recognizing self-epitopes presented on MHC or HLA complex. They are a key part of the adaptive immune system and highly antigen-specific. T cells can specifically target these antigens through their surface T Cell Receptors (TCRs), which diversify through V(D)J recombination to create multitudes of unique clones.
There are two distinct classes of T cells, CD8+ T cells that recognize epitopes on MHC-I, and CD4+ T cells that recognize epitopes on MHC-II. The epitopes presented on MHC-I are shorter, 8-12 amino acids in length, while those presented by MHC-II are longer, 10-25 amino acids. MHC-I are on all nucleated cells but MHC-II are usually just on professional APCs, like B cells, DCs, and macrophages. Central and peripheral tolerance mechanisms restrict self-reactive T cells, but T cells can sometimes recognize self-antigens in MHC molecules due to tolerance failure.
The MHC-I pathway presents peptides from intracellular sources, like viral or endogenous proteins, to CD8+ T cells. These proteins are degraded by the proteasome, and the resulting peptides are transported into the ER and loaded onto MHC-I molecules. In contrast, MHC-II pathway collects extracellular proteins, which are internalized, processed in endosomes, and presented on MHC-II molecules to CD4+ T cells.
Most T-cells normally react to just one specific antigen, but studies in MS and long-term EBV carriers find high amounts of EBV-specific CD4+ and CD8+T-cells are polyfunctional cells (PFCs). PFCs have less functional avidity, but retain their antigen-specific proliferation capacity. As they are less susceptible to activation-induced cell death, it’s thought they are essential in persistent antigen exposure and high viral load. The increased presence of these cells, combined with selectively impaired cytokines, indicates immune dysfunction driven by viral dominance and enhanced neuroinflammation.
EBV can also lower endogenous glutathione (GSH) in the body when it reactivates for the lytic replication phase. Ferroptosis, a programmed cell death pathway caused by uncontrolled lipid peroxidation that destroys cellular membranes also needs GSH lowered to occur. If latent EBV reactivates to lytic phase coincident with elevated heavy metal concentrations, they can react with H202 to form hydroxyl radicals. These degrade lipid membranes (lipid peroxidation) that can lead to ferroptosis of oligodendrocytes. This is a little far fetched, but anything that either induces OL death to cause demyelination or myelin degradation that that releases myelin components would suffice. Insufficient OL supports to axons, neuronal stresses, increased ROS or cytokines, and glial cell activation are just some examples that could cause this.
In summary, low vitamin D levels in childhood and adolescence along with the HLA-DRB1-15 haplotype create a high EBV viral load upon primary infection. Either through OL apoptosis or myelin sheath degradation, citrullinated MBP fragments are released into the CNS extracellular environment. These are captured by an EBV-infected MBC that goes through autophagy and processes a neoepitope. It presents it to a CD4+ T cell with an EBV-induced higher Th1 response which proliferates and sends out signals to bring together numerous peripheral adaptive immune cells and adhesion molecules. All of these cells produce huge amounts of pro-inflammatory cytokines that transiently weaken the BBB allowing them to infiltrate into the CNS. Inside they create extensive inflammation at the original damage site that leads to more demyelination and the initial MS attack. The extensive myelin damage releases other immunoreactive myelin sheath components that can be presented through both MHCI and II on APCs to CD4+ and CD8+ T cells. It also induces antigen cross-presentation between EBV and myelin sheath components due to molecular mimicry.
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