Interaction of the Gut Microbiome and Immunity in Multiple Sclerosis: Impact of Diet and Immune Therapy.

The bidirectional communication between the gut and central nervous system (CNS) through microbiota is known as the microbiota-gut-brain axis. The brain, through the enteric neural innervation and the vagus nerve, influences the gut physiological activities (motility, mucin, and peptide secretion), as well as the development of the mucosal immune system. Conversely, the gut can influence the CNS via intestinal microbiota, its metabolites, and gut-homing immune cells. Growing evidence suggests that gut immunity is critically involved in gut-brain communication during health and diseases, including multiple sclerosis (MS). The gut microbiota can influence the development and function of gut immunity, and conversely, the innate and adaptive mucosal immunity can influence microbiota composition. Gut and systemic immunity, along with gut microbiota, are perturbed in MS. Diet and disease-modifying therapies (DMTs) can affect the composition of the gut microbial community, leading to changes in gut and peripheral immunity, which ultimately affects MS. A high-fat diet is highly associated with gut dysbiosis-mediated inflammation and intestinal permeability, while a high-fiber diet/short-chain fatty acids (SCFAs) can promote the development of Foxp3 Tregs and improvement in intestinal barrier function, which subsequently suppress CNS autoimmunity in the animal model of MS (experimental autoimmune encephalomyelitis or EAE). This review will address the role of gut immunity and its modulation by diet and DMTs via gut microbiota during MS pathophysiology.

Gut dysbiosis breaks immunological tolerance toward the central nervous system during young adulthood.

Multiple sclerosis (MS) is an autoimmune disease targeting the central nervous system (CNS) mainly in young adults, and a breakage of immune tolerance to CNS self-antigens has been suggested to initiate CNS autoimmunity. Age and microbial infection are well-known factors involved in the development of autoimmune diseases, including MS. Recent studies have suggested that alterations in the gut microbiota, referred to as dysbiosis, are associated with MS. However, it is still largely unknown how gut dysbiosis affects the onset and progression of CNS autoimmunity. In this study, we investigated the effects of age and gut dysbiosis on the development of CNS autoimmunity in humanized transgenic mice expressing the MS-associated MHC class II (MHC-II) gene, HLA-DR2a, and T-cell receptor (TCR) genes specific for MBP87-99/DR2a that were derived from an MS patient. We show here that the induction of gut dysbiosis triggers the development of spontaneous experimental autoimmune encephalomyelitis (EAE) during adolescence and early young adulthood, while an increase in immunological tolerance with aging suppresses disease onset after late young adulthood in mice. Furthermore, gut dysbiosis induces the expression of complement C3 and production of the anaphylatoxin C3a, and down-regulates the expression of the Foxp3 gene and anergy-related E3 ubiquitin ligase genes. Consequently, gut dysbiosis was able to trigger the development of encephalitogenic T cells and promote the induction of EAE during the age window of young adulthood.

Friend or foe? Targeting microglia in Alzheimer's disease.

Inflammation is believed to be a component of a number of degenerative brain diseases including Alzheimer's disease. A recent article by Fu and colleagues (2016) demonstrated that the cytokine IL-33 can modulate microglia in an animal model of AD to become better scavengers of beta-amyloid and less pro-inflammatory. The findings have potential therapeutic implications for a number of brain conditions.

Advances in the immunopathogenesis of multiple sclerosis.

PURPOSE OF REVIEW: Recent studies indicate a role for immune dysregulation in the pathogenesis of multiple sclerosis, an inflammatory demyelinating and degenerative disease of the central nervous system. This review addresses the current mechanisms of immune dysregulation in the development of multiple sclerosis, including the impact of environmental risk factors on immunity in both multiple sclerosis and its animal models. RECENT FINDINGS: CD4 T-helper (Th) cells have long been implicated as the main drivers of pathogenesis of multiple sclerosis. However, current studies indicate that multiple sclerosis is largely a heterogeneous disease process, which involves both innate and adaptive immune-mediated inflammatory mechanisms that ultimately contribute to demyelination and neurodegeneration. Therefore, B cells, CD8 T cells, and microglia/macrophages can also play an important role in the immunopathogenesis of multiple sclerosis apart from proinflammatory CD4 Th1/Th17 cell subsets. Furthermore, increasing evidence indicates that environmental risk factors, such as Vitamin D deficiency, Epstein-Barr virus, smoking, Western diet, and the commensal microbiota, influence the development of multiple sclerosis through interactions with genetic variants of multiple sclerosis, thus leading to the dysregulation of immune responses. SUMMARY: A better understanding of immune-mediated mechanisms in the pathogenesis of multiple sclerosis and the contribution of environmental risk factors toward the development of multiple sclerosis will help further improve therapeutic approaches to prevent disease progression.

The choroid plexus and the paradox of interferons in the aging brain.

The choroid plexus (CP) function is largely viewed as the source of cerebrospinal fluid (CSF) and as a barrier between the blood and the CSF. Other functions of the CP are becoming increasingly recognized as in the recent publication by Baruch et. al. who demonstrate increased expression of interferon type I mRNA signature (irf7, ifnß and ifit1) in CP of aged brains compared to younger brains, whereas interferon type II dependent genes (icam1, cxcl10, and ccl17) are reduced in the aging CP. The authors speculate an IFN-dependent mechanism that plays a role in the aging process and cognitive decline. This short communication summarizes the findings by the authors and highlights the seemingly paradoxical roles of IFN type I and type II in neuroinflammation.

Microglia and necroptosis: The culprits of neuronal cell death in multiple sclerosis.

Multiple Sclerosis is an inflammatory demyelinating and degenerative disease of the central nervous system in which activated microglia contribute to oligodendroglial, neuronal, and axonal damage. A recent study (summarized here) provided evidence for a role of necroptosis in MS brain tissue based on reduced caspase-8 and increased expression of cFLIP in microglial cells. In addition, activation of RIPK1, RIPK3, and MLKL (molecules characteristic of necroptosis) was demonstrated in cortical lesions from MS brain specimens. Defective caspase-8 activity in microglia adds a new dimension to microglial role in MS and provides a potential therapeutic target in the progressive forms of the disease.

Monthly triple-dose gadolinium administration: potential associations with leukopenia, hypophosphatemia, and bone marrow T1 hyperintensity.

OBJECTIVE: Monthly scanning with triple-dose gadopentetate dimeglumine has been shown to be associated with progressive increases in bone T1 hyperintensity, hypophosphatemia, and leukopenia. This study was performed to retrospectively investigate the potential associations among these phenomena. METHODS: This retrospective analysis involved patients who had received monthly triple-dose gadopentetate dimeglumine for up to 2 years as part of treatment for multiple sclerosis. Monthly magnetic resonance imaging scans of the brain (n = 67) were segmented to evaluate the signal intensity in the cranial marrow. Potential associations among the marrow T1 hyperintensity, serum phosphate concentration, and white blood cell count were examined. RESULTS: Patients in the no leukopenia group showed a statistically significant mean monthly increase in the bone marrow signal-to-noise ratio of 0.0430/month. Patients in the leukopenia group showed a mean monthly increase in the bone marrow signal-to-noise ratio of 0.0398/month, but this was not statistically significant. Patients in the hypophosphatemia group were significantly less likely to develop leukopenia than patients who had never developed hypophosphatemia. CONCLUSIONS: Although monthly administration of triple-dose gadopentetate dimeglumine over 13 months has been associated with progressive increases in leukopenia, hypophosphatemia, and T1 signal intensity of bone, this study showed an inverse relationship between leukopenia and hypophosphatemia.

Fecal Lcn-2 level is a sensitive biological indicator for gut dysbiosis and intestinal inflammation in multiple sclerosis.

Multiple Sclerosis (MS) has been reported to be associated with intestinal inflammation and gut dysbiosis. To elucidate the underlying biology of MS-linked gut inflammation, we investigated gut infiltration of immune cells during the development of spontaneous experimental autoimmune encephalomyelitis (EAE) in humanized transgenic (Tg) mice expressing HLA-DR2a and human T cell receptor (TCR) specific for myelin basic protein peptide (MBP87-99)/HLA-DR2a complexes. Strikingly, we noted the simultaneous development of EAE and colitis, suggesting a link between autoimmune diseases of the central nervous system (CNS) and intestinal inflammation. Examination of the colon in these mice revealed the infiltration of MBP-specific Th17 cells as well as recruitment of neutrophils. Furthermore, we observed that fecal Lipocalin-2 (Lcn-2), a biomarker of intestinal inflammation, was significantly elevated and predominantly produced by the gut-infiltrating neutrophils. We then extended our findings to MS patients and demonstrate that their fecal Lcn-2 levels are significantly elevated compared to healthy donors (HDs). The elevation of fecal Lcn-2 levels correlated with reduced bacterial diversity and increased levels of other intestinal inflammation markers including neutrophil elastase and calprotectin. Of interest, bacteria thought to be beneficial for inflammatory bowel disease (IBD) such as Anaerobutyricum, Blautia, and Roseburia, were reduced in fecal Lcn-2-high MS patients. We also observed a decreasing trend in serum acetate (a short-chain fatty acid) levels in MS Lcn-2-high patients compared to HDs. Furthermore, a decrease in the relative abundance of Blautia massiliensis was significantly associated with a reduction of acetate in the serum of MS patients. This study suggests that gut infiltration of Th17 cells and recruitment of neutrophils are associated with the development of gut dysbiosis and intestinal inflammation, and that fecal Lcn-2 level is a sensitive biological indicator for gut dysbiosis in multiple sclerosis.

Interferon-ß inhibits toll-like receptor 9 processing in multiple sclerosis.

OBJECTIVE: Viral infections have been implicated in the pathogenesis of multiple sclerosis (MS). Plasmacytoid dendritic cells (pDCs) are present in peripheral blood, cerebrospinal fluid, and brain lesions of MS patients. pDCs sense viral DNA via Toll-like receptor 9 (TLR9), which has to be cleaved from the N-terminal to become functional (TLR9 processing). pDCs activated with TLR9 agonists promote T-helper type 1 (Th1)/T-helper type 17 (Th17) responses. In the animal model of MS, TLR9 agonists can induce disease. We hypothesized that pDCs are inhibited by disease-modifying therapy such as interferon (IFN)-ß, consequently decreasing the frequency of MS attacks. METHODS: We separated pDCs from healthy subjects and patients diagnosed with relapsing-remitting MS and clinically isolated syndrome. Cytokine secretion by pDCs activated with TLR9 agonists was measured by enzyme-linked immunosorbent assay and multianalyte profiling. TLR9 gene and protein expression was studied by DNA microarrays and western blot. RESULTS: In untreated patients, pDCs activated with TLR9 agonists produced increased levels of IFN-α, a Th1-promoting cytokine, as compared to healthy subjects. In IFN-ß-treated patients, activated pDCs had decreased ability to produce both IFN-α and the proinflammatory cytokines interleukin (IL)-6 and tumor necrosis factor α as compared to untreated patients. pDCs separated from IFN-ß-treated patients had significantly reduced levels of the processed TLR9 protein but normal levels of the full-length TLR9 protein and TLR9 gene expression as compared to untreated patients. INTERPRETATION: This finding represents a novel immunomodulatory mechanism of IFN-ß: inhibition of TLR9 processing. This results in decreased activation of pDCs by viral pathogens and, thus, may affect the frequency of MS exacerbations.

Potential Risks and Benefits of Multiple Sclerosis Immune Therapies in the COVID-19 Era: Clinical and Immunological Perspectives.

Coronavirus SARS-CoV2 has emerged as one of the greatest infectious disease health challenges in a century. Patients with multiple sclerosis (MS) have a particular vulnerability to infections through their use of immunosuppressive disease-modifying therapies (DMTs). Specific DMTs pose particular risk based on their mechanisms of action (MOA). As a result, patients require individualized approaches to starting new treatments and continuation of therapy. Additionally, vaccinations must be considered carefully, and individuals on long-term B cell-depleting therapies may have diminished immune responses to vaccination, based on preserved T cells and diminished but present antibody titers to influenza vaccines. We review the immunology behind these treatments and their impact on COVID-19, as well as the current recommendations for best practices for use of DMTs in patients with MS.

Effect of switching glatiramer acetate formulation from 20 mg daily to 40 mg three times weekly on immune function in multiple sclerosis.

BACKGROUND: Many RRMS patients who had been treated for over 20 years with GA 20 mg/ml daily (GA20) switched to 40 mg/ml three times-a-week (GA40) to reduce injection-related adverse events. Although GA40 is as effective as GA20 in reducing annualized relapse rate and MRI activity, it remains unknown how switching to GA40 from GA20 affects the development of pathogenic and regulatory immune cells. OBJECTIVE: To investigate the difference in immunological parameters in response to GA20 and GA40 treatments. METHODS: We analyzed five pro-inflammatory cytokines (IL-1ß, IL-23, IL-12, IL-18, TNF-α), and three anti-inflammatory/regulatory cytokines (IL-10, IL-13, and IL-27) in serum. In addition, we analyzed six cytokines (IFN-γ, IL-17A, GM-CSF, IL-10, IL-6, and IL-27) in cultured PBMC supernatants. The development of Th1, Th17, Foxp3 Tregs, M1-like, and M2-like macrophages were examined by flow cytometry. Samples were analyzed before and 12 months post switching to GA40 or GA20. RESULTS: Pro- and anti-inflammatory cytokines were comparable between the GA40 and GA20 groups. Development of Th1, Th17, M1-like macrophages, M2-like macrophages, and Foxp3 Tregs was also comparable between the two groups. CONCLUSIONS: The immunological parameters measured in RRMS patients treated with GA40 three times weekly are largely comparable to those given daily GA20 treatment.

Dimethyl Fumarate Suppresses Demyelination and Axonal Loss through Reduction in Pro-Inflammatory Macrophage-Induced Reactive Astrocytes and Complement C3 Deposition.

Dimethyl fumarate (DMF) is an oral agent for relapsing-remitting multiple sclerosis (RRMS). In this study, we investigated the therapeutic mechanism of DMF using experimental autoimmune encephalomyelitis (EAE). DMF treatment decreased the proliferation of T cells and the production of IL-17A and GM-CSF. DMF treatment also decreased the development and/or infiltration of macrophages in the central nervous system (CNS), and reduced the ratio of iNOS+ pro-inflammatory macrophage versus Ym1+ immunomodulatory macrophages. Furthermore, DMF treatment suppressed the deposition of complement C3 (C3) and development of reactive C3+ astrocytes. The decrease in iNOS+ macrophages, C3+astrocytes, and C3 deposition in the CNS resulted in the reduction in demyelination and axonal loss. This study suggests that the beneficial effects of DMF involve the suppression of iNOS+ pro-inflammatory macrophages, C3+ astrocytes, and deposition of C3 in the CNS.

MRI demonstration of gadolinium deposition in bone after monthly triple-dose gadopentetate dimeglumine and correlation with frequency of hypophosphatemia.

OBJECTIVES: We retrospectively analyzed data of the BECOME trial to investigate whether serial administration of triple-dose (3-dose) gadopentetate dimeglumine would result in the development of T1 signal-to-noise (S/N) changes in the cranial diploic space and whether S/N changes correlated with on-study hypophosphatemia. METHODS: Signal intensity analysis was performed on the first year's data of the BECOME trial using 3-dose Gd (14 months, maximum number of doses, 39, mean: 36). Routine blood and urine tests were obtained each month for safety monitoring. Linear mixed regression modeling with random intercept was used to analyze monthly signal-to-noise ratio (S/N = Bone/Air) using an ROI of the diploic space created from T2W images and overlaid on T1FS (T1 fat-saturated) images. Incidence of phosphate abnormalities was analyzed using the general estimation equation; correlation of phosphate and S/N change was achieved with type 3 test of fixed effects. RESULTS: Cranial diploic space T1FS S/N increased over 14 months: S/N = 0.039 mean monthly increase (S.E. 0.008; p < 0.0001). Subjects with consistently normal phosphate levels (n = 32) experienced more of a S/N increase than patients with at least one episode of hypophosphatemia (n = 35) (0.057 vs. 0.023, respectively, p = 0.037). Those with moderate hypophosphatemia demonstrated no significant S/N increase. CONCLUSION: Monthly administration of 3-dose gadopentetate dimeglumine is associated with development of increased S/N on T1FS imaging in the cranial diploic space, suggesting Gd retention in bone. Our data suggests MRI could be used as a noninvasive method of tracking Gd retention in bone, which was more pronounced in patients with normal phosphate levels.

Protective autoimmunity in the nervous system.

The immune system can play both detrimental and beneficial roles in the nervous system. Multiple arms of the immune system, including T cells, B cells, NK cells, mast cells, macrophages, dendritic cells, microglia, antibodies, complement and cytokines participate in limiting damage to the nervous system during toxic, ischemic, hemorrhagic, infective, degenerative, metabolic and immune-mediated insults and also assist in the process of repair after injury has occurred. Immune cells have been shown to produce neurotrophic growth factors and interact with neurons and glial cells to preserve them from injury and stimulate growth and repair. The immune system also appears to participate in proliferation of neural progenitor stem cells and their migration to sites of injury. Neural stem cells can also modify the immune response in the central and peripheral nervous system to enhance neuroprotective effects. Evidence for protective and reparative functions of the immune system has been found in diverse neurologic diseases including traumatic injury, ischemic and hemorrhagic stroke, multiple sclerosis, infection, and neurodegenerative diseases (Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis). Existing therapies including glatiramer acetate, interferon-beta and immunoglobulin have been shown to augment the protective and regenerative aspects of the immune system in humans, and other experimental interventions such as vaccination, minocycline, antibodies and neural stem cells, have shown promise in animal models of disease. The beneficent aspects of the immune response in the nervous system are beginning to be appreciated and their potential as pharmacologic targets in neurologic disease is being explored.

Fibrinolysis induced clinical improvement in a patient with multiple sclerosis exacerbation.

BACKGROUND: Recently, extravascular fibrinogen leakage has emerged as a potential trigger of local neuroinflammation in the CNS. In the animal models of MS, fibrin depletion decreased neuroinflammation and neurodegeneration. The role of fibrinolytic therapy in patients with MS has not been studied. OBJECTIVE: To describe a unique case of rapid clinical improvement after fibrinolytic therapy in a patient with MS and symptomatic acute demyelinating lesion. METHODS: The MS patient with acute right-sided weakness was thought to have a stroke and received intravenous recombinant tissue plasminogen activator (rtPA). Serial neurological exams and MRI were performed. RESULTS/CONCLUSION: In 5.4 hours after rtPA administration, NIH Stroke Scale score improved from 9 to 1, and this improvement persisted until 21 hours from symptom onset, approximate duration of rtPA action. Brain MRI revealed a symptomatic acute demyelinating lesion with restricted diffusion. We suggest that fibrin may serve as a potential therapeutic target in a subset of people with MS.

Surface Layer Protein A Expressed in Clostridioides difficile DJNS06-36 Possesses an Encephalitogenic Mimotope of Myelin Basic Protein.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS). Recent studies suggest that migration of Th1 and Th17 cells specific for enteric bacteria from the gut to the CNS may lead to the initiation and/or exacerbation of autoimmune diseases including MS. Human leukocyte antigen (HLA)-DR15 is an MHC class II (MHCII) haplotype highly associated with the development of MS that contains the two HLA-DRB* genes, DRB1*1501 (DR2b) and DRB5*0101 (DR2a). To identify enteric bacteria which harbor antigenic epitopes that activate myelin-specific T cells and drive CNS inflammation, we screened for enteric bacteria which express cross-reactive epitopes ('mimotopes') of an immunodominant myelin basic protein 89-98 (MBP89-98) epitope. Based on known MHCII HLA-DR2a amino acid binding motifs and cultivation with splenic T cells isolated from MBP-T cell receptor (TCR)/DR2a transgenic (Tg) mice, we discovered that a certain variant of surface layer protein A (SLPA), which is expressed by a subtype of Clostridioides difficile, contains an amino acid sequence that activates MBP89-98-reactive T cells. Furthermore, activation of MBP-specific T cells by SLPA upon active immunization induced experimental autoimmune encephalomyelitis (EAE) in MBP-TCR/DR2a Tg mice. This study suggests that a unique strain of C. difficile possesses an encephalitogenic mimotope of MBP that activates autoreactive, myelin-specific T cells.

Gray Matter Nucleus Hyperintensity After Monthly Triple-Dose Gadopentetate Dimeglumine With Long-term Magnetic Resonance Imaging.

OBJECTIVES: Gadolinium deposition is widely believed to occur, but questions regarding accumulation pattern and permanence remain. We conducted a retrospective study of intracranial signal changes on monthly triple-dose contrast-enhanced magnetic resonance imaging (MRI) examinations from the previously published Betaseron vs. Copaxone in Multiple Sclerosis With Triple-Dose Gadolinium and 3-Tesla MRI Endpoints Trial (N = 67) to characterize the dynamics of gadolinium deposition in several deep brain nuclei and track persistence versus washout of gadolinium deposition on long-term follow-up (LTFU) examinations (N = 28) obtained approximately 10 years after enrollment in the Betaseron vs. Copaxone in Multiple Sclerosis With Triple-Dose Gadolinium and 3-Tesla MRI Endpoints Trial. MATERIALS AND METHODS: Using T2 and proton density images and using image analysis software (ITK-SNAP), manual regions of interest were created ascribing boundaries of the caudate nucleus, dentate nucleus, globus pallidus, pulvinar, putamen, white matter, and air. Intensity analysis was conducted on T1-weighted fat-saturated (fat-sat) images using the FSL package. A linear rigid-body transform was calculated from the fat-sat image at each target time point to the region of interest segmentation reference time point fat-sat image. Serial MRI signal was analyzed using linear mixed regression modeling with random intercept. Annual MRI signal changes including LTFU scans were assessed with t test. RESULTS: During monthly scanning, all gray matter structures demonstrated a significant (P < 0.0001) increase in contrast-to-noise ratio. Yearly changes in deposition showed distinctive patterns for the specific nucleus: globus pallidus showed complete retention, pulvinar showed partial washout, while dentate, caudate, and putamen returned to baseline (ie, complete washout). CONCLUSIONS: Monthly increased contrast-to-noise ratio in gray matter nuclei is consistent with gadolinium deposition over time. The study also suggests that some deep gray matter nuclei permanently retain gadolinium, whereas others demonstrate washout of soluble gadolinium.

Insight into the mechanism of action of dimethyl fumarate in multiple sclerosis.

Dimethyl fumarate (DMF) is an oral, disease-modifying agent for the treatment of relapsing-remitting multiple sclerosis (RRMS). However, details regarding its mode of action are still emerging. It is believed that the mode of action of DMF involves both nuclear factor erythroid-derived 2-related factor (Nrf2)-dependent and independent pathways, which lead to an anti-inflammatory immune response due to type II myeloid cell and Th2 cell differentiation and neuroprotection. In this review, we will focus on the molecular and signaling effects of DMF that lead to changes in peripheral immune cell composition and function, alteration in CNS cell-specific functions, and effect on the blood-brain barrier.