The role of infections in the pathogenesis and course of multiple sclerosis

Non-infectious mechanisms of neurological damage due to infection

Infections of the nervous system is a growing aspect of clinical neurology. Accumulating knowledge in early diagnosis, course, therapy and prognosis is enlarging the clinical tools required for effective therapy. Of special importance is the ability to differentiate between proper infections, where anti-microbial agents, when available, should be introduced and used and post infectious conditions where therapy is mainly directed against the host immune system. The two conditions sometimes overlap, a situation that requires the ability to combine clinical skills with the use of laboratory tools such as polymerase chain reaction (PCR), serology, and antigenic detection. In the era of the SARS-CoV-2 pandemic, the need to make this distinction is emphasized as correct diagnosis of post infectious conditions and expedited therapy is important and sometimes lifesaving. We here attempt to present several infectious agents and their possible indirect damage to the nervous system causing in some cases significant neurological deficits. We try to limit our focus on those mechanisms which do not involve the direct tissue damage by the infectious agents but rather are connected to para- and post-infectious mechanisms. We attempt to delineate the features that will enable to tailor the correct diagnosis and following the effective therapy.

Immune-mediated genesis of multiple sclerosis

Multiple sclerosis (MS) is widely acknowledged to be an autoimmune disease affecting the neuronal myelin structure of the CNS. Autoantigens recognized as the target of this autoimmune process are: myelin basal protein, anti-proteolipid protein, antimyelin-associated glycoprotein and antimyelin-based oligodendrocytic basic protein. Ample evidence supports the idea of a dysregulation of immunological tolerance towards self-antigens of neuronal myelin structure triggered by one or more viral or bacterial microbial agents in predisposed HLA gene subjects. Genetic predisposition to MS has been highlighted by numerous studies associating the disease to specific HLA haplotypes. Moreover, a wide range of evidence supports the fact that MS may be consequence of one or more viral or bacterial infections such as measles virus, EBV, HHV6, HZV, Chlamydia pneumoniae, Helicobacter Pylori, and other microbial agents. Microbiota elements also seems to have a role on the determinism of the disease as a pathogenic or protective factor. The autoimmune pathogenetic process could arise when a molecular mimicry between a foreign microbial antigen and an auto-antigen occurs in an HLA gene subject competent for that particular antigen. The antigen-presenting cells in this case would induce the activation of a specific Th clone causing a cross-reaction between a foreign antigen and an autoantigen resulting in an autoimmune response.

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A multifactorial ethiopathogenetic model based on immunomediation is a reliable hypothesis for multiple sclerosis.

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Evidence found in the scientific literature makes it possible to reconstruct this etiopathogenetic hypothesis for MS.

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HLA gene predisposition, correlation with infections, molecular mimicry and other immunological data are reported.

Differential serostatus of Epstein-Barr virus in Iranian MS patients with various clinical patterns

Background: Epidemiological evidence suggests a role of Epstein-Barr virus (EBV) in triggering the pathogenesis of Multiple Sclerosis (MS). The aim of this study was to assess the EBV-specific antibodies in MS patients with various clinical patterns and their association with the production of IFN-γ, IL-12, and IL-4 cytokines compared with healthy individuals.

Methods: We measured EBNA-1 IgG, VCA IgG, and production of IFN-γ, IL-12 and IL-4 cytokines in patients with different clinical patterns and healthy controls using ELISA method.

Results: There was a higher titer of anti-EBV antibodies in MS patients compared to healthy controls. SPMS patients generated higher EBNA-1 levels than those with RRMS and PPMS patients whereas; the level of VCA IgG was higher in the RRMS patients than PPMS. In PPMS patients, a significant increase was found in IFN-γ and IL-12 cytokines compared to other subtypes, whereas IL-4 cytokine had a decreased level compared to RRMS patients. Higher anti-EBV antibodies are associated with increased IL-12 cytokine in RRMS patients. However, no significant correlation was found between these antibodies and other secreted cytokines.

Conclusion: EBV infection is one of the strong risk factors for MS. Acting on these factors could be useful to decrease the incidence and disease exacerbation of MS. Study of the antibody levels to EBV virus could be useful for evaluating MS risk score in each clinical subtypes.

Metronidazole Attenuates the Intensity of Inflammation in Experimental Autoimmune Uveitis

Autoimmune uveitis is a serious sightthreatening disease that in many cases fails to respond to conventional immunosuppressive or biological therapy. Experimental models used in research allow more detailed study of pathogenesis of the autoimmune process and testing new therapeutic strategies. Recent results show that infection can trigger autoimmune diseases, and some commensal microorganisms are essential in causing disease activity. The aim of this work was to assess the effect of broadspectrum antibiotics - combination of metronidazole and ciprofloxacin or metronidazole alone - on the intensity of intraocular inflammation in experimental autoimmune uveitis (EAU). EAU was induced in mouse strain C57BL/6J by interphotoreceptor retinoid- binding protein in complete Freund's adjuvant and pertussis toxin. The grade of uveitis was assessed clinically and histologically in haematoxylin and eosin- stained tissues. Lymphocytes and macrophages were detected in cryosections using the immunoperoxidase method with antibodies. The therapy was commenced one week before EAU induction and continued throughout the experiment. In addition, metronidazole treatment was also started two weeks before EAU induction. Antibiotics significantly reduced the intensity of uveitis compared to the control group (P < 0.05). The effects of combination of ciprofloxacin and metronidazole and of metronidazole alone were similar when the therapy started one week before EAU induction (P < 0.05). Metronidazole commenced two weeks before EAU induction and throughout the experiment suppressed the intensity of EAU with even higher statistical significance (P < 0.0001). It can be assumed that the high protective effect of metronidazole on EAU intensity may be due not only to its antimicrobial effect, but also to its immunomodulatory activity.

Latitude, Vitamin D, Melatonin, and Gut Microbiota Act in Concert to Initiate Multiple Sclerosis: A New Mechanistic Pathway

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS). While the etiology of MS is still largely unknown, scientists believe that the interaction of several endogenous and exogenous factors may be involved in this disease. Epidemiologists have seen an increased prevalence of MS in countries at high latitudes, where the sunlight is limited and where the populations have vitamin D deficiency and high melatonin levels. Although the functions and synthesis of vitamin D and melatonin are contrary to each other, both are involved in the immune system. While melatonin synthesis is affected by light, vitamin D deficiency may be involved in melatonin secretion. On the other hand, vitamin D deficiency reduces intestinal calcium absorption leading to gut stasis and subsequently increasing gut permeability. The latter allows gut microbiota to transfer more endotoxins such as lipopolysaccharides (LPS) into the blood. LPS stimulates the production of inflammatory cytokines within the CNS, especially the pineal gland. This review summarizes the current findings on the correlation between latitude, sunlight and vitamin D, and details their effects on intestinal calcium absorption, gut microbiota and neuroinflammatory mediators in MS. We also propose a new mechanistic pathway for the initiation of MS.

Oral infection with P. gingivalis exacerbates autoimmune encephalomyelitis

BACKGROUND

Oral infection of mice with P. gingivalis induces periodontal inflammation and attachment loss. The aim of the present study was to investigate whether infection of mice with P. gingivalis, exacerbates the clinical course of experimental autoimmune encephalomyelitis (EAE)-a mouse model of multiple sclerosis (MS).

METHODS

Induction of EAE was carried out by immunization of C57BL/6 mice with myelin oligodentrocyte glycoprotein (MOG_35-55 ). P. gingivalis infection was induced via subcutaneous chambers model and the oral gavage. The severity of EAE was measured using a clinical severity score. Ex-vivo reactivation of lymphocytes with the encephalitogenic peptide MOG_35-55 was also tested.

RESULTS

Subcutaneous as well as oral infection with live P. gingivalis led to significant aggravation of the severity of EAE. Lymph node cells harvested from mice with EAE following P. gingivalis infection showed augmented lymphocyte proliferation towards the encephlatigenic MOG moiety compared to mice with EAE only.

CONCLUSIONS

The present results indicate that oral infection with P. gingivalis augmented the severity of EAE. This may stem from the systemic pro-inflammatory response triggered by P. gingivalis infection or via antigen mimicking. The present study provides evidence that periodontal infection may play a role as modifier in CNS inflammatory disorders, such as MS.

Prevalence of Cytomegalovirus in Patients With Multiple Sclerosis: A Case-Control Study in Northern Iran

BACKGROUND

Multiple sclerosis (MS) is a chronic debilitating disease known as one of the most common neurological dysfunctions in young adults. Recent studies suggest that infections with herpesviruses play a critical role in the pathogenesis of MS.

OBJECTIVES

The present investigation aimed to detect the presence of cytomegalovirus (CMV) in patients with MS using polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) methods.

PATIENTS AND METHODS

Plasma and peripheral blood mononuclear cells (PBMCs) were collected from MS patients (n = 82) and from blood donors as control group (n = 89). They were tested for the presence of CMV antibodies and DNA by ELISA and PCR, respectively.

RESULTS

Anti-CMV was positive in 65 (79.3%) and 69 (77.5%) of the MS patients and healthy subjects, respectively (P= 0.853). Similarly, 23 (28%) and 2 (2.2%) patients were positive for CMV DNA among the MS and control groups, respectively. Statistical analysis showed that the frequency of CMV DNA in the MS patients was significantly higher than in the healthy controls (P < 0.001).

CONCLUSIONS

The results of this study showed a possible association between CMV infection and MS. Further experimental and epidemiological studies using case-control approaches are needed to confirm this association.

The Microbiota Determines Susceptibility to Experimental Autoimmune Uveoretinitis

The microbiota is a crucial modulator of the immune system. Here, we evaluated how its absence or reduction modifies the inflammatory response in the murine model of experimental autoimmune uveoretinitis (EAU). We induced EAU in germ-free (GF) or conventionally housed (CV) mice and in CV mice treated with a combination of broad-spectrum antibiotics either from the day of EAU induction or from one week prior to induction of disease. The severity of the inflammation was assessed by fundus biomicroscopy or by histology, including immunohistology. The immunophenotyping of T cells in local and distant lymph nodes was performed by flow cytometry. We found that GF mice and mice where the microbiota was reduced one week before EAU induction were protected from severe autoimmune inflammation. GF mice had lower numbers of infiltrating macrophages and significantly less T cell infiltration in the retina than CV mice with EAU. GF mice also had reduced numbers of IFN-γ and IL-17-producing T cells and increased numbers of regulatory T cells in the eye-draining lymph nodes. These data suggest that the presence of microbiota during autoantigen recognition regulates the inflammatory response by influencing the adaptive immune response.

Identifying clues to molecular etiology of multiple sclerosis in South Indian patients

BACKGROUND

Environmental risk factors have a dominant role in the pathogenesis of multiple sclerosis (MS). Unhealthy lifestyle can predispose people to autoimmune diseases. MS was a rare disease in Kerala, but now, we notice frequent cases of MS at the city neurology clinic. Changing lifestyle and associated changes in the level of proinflammatory biomolecules like: leptin, soluble leptin receptor (SLR) and free fatty acids (FA) could be contributing to rise in MS incidence.

OBJECTIVE

To identify variations in the levels of bio-molecules: leptin, SLR and FA, between MS patients and matched healthy control.

METHOD

Leptin and SLR levels in the blood serum, were estimated using ELISA, while total FA levels, were estimated using an enzyme based calorimetric assay.

RESULT

Mean serum FA levels in MS patients (31.39 ± 4.83 nmole/100 μl) were 2.7 fold higher than controls (11.54 ± 2.66 nmoles/100 μl) at more than 99% CI. The differences in mean leptin and SLR levels were not statistically significant.

CONCLUSION

MS patients had high level of total FA in their blood. High FA in blood may have a role in MS pathogenesis. More in-depth study is required to understand the precise mechanism by which FA rise in MS blood sample can contribute to pathogenesis.

The long and evolving relationship between viruses and multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disorder of unknown etiology, possibly caused by a virus or is virus-triggered. Several viruses, including herpesviruses, were suggested as etiologic agents or risk factors for exacerbation in the course of illness but none have been shown to be irrefutably linked. Recently the interest of researchers and clinicians in the association between viruses and MS was reawakened by the development of progressive multifocal leukoencephalopathy, a demyelinating and fatal disease caused by JC polyomavirus replication, in natalizumab-treated MS patients. In this review, we will illustrate the evidence underlying the viral hypothesis for MS pathogenesis and will review the main features of the potential viral candidates. We will also describe the risks associated with newer MS therapies and with viral/bacterial vaccinations.

Peptidoglycan: a critical activator of the mammalian immune system during infection and homeostasis

Peptidoglycan is a conserved structural component of the bacterial cell wall with molecular motifs unique to bacteria. The mammalian immune system takes advantage of these properties and has evolved to recognize this microbial associated molecular pattern. Mammals have four secreted peptidoglycan recognition proteins, PGLYRP-1-4, as well as two intracellular sensors of peptidoglycan, Nod1 and Nod2. Recognition of peptidoglycan is important in initiating and shaping the immune response under both homeostatic and infection conditions. During infection, peptidoglycan recognition drives both cell-autonomous and whole-organism defense responses. Here, we examine recent advances in the understanding of how peptidoglycan recognition shapes mammalian immune responses in these diverse contexts.

Role of glial cells in innate immunity and their role in CNS demyelination

The adaptive and innate arms of the immune system are the two pillars of host defense against environmental pathogens. Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS which is considered to be autoimmune and is thought to result from breakdown in the usual checks and balances of the adaptive immune response. The major pathological outcome of the disease is "the MS plaque" a unique feature of CNS demyelination characterized by the destruction of oligodendrocytes with loss of myelin and underlying axons. The MS plaque is not seen in other inflammatory disorders of the CNS. The prevailing opinion suggests that MS is mediated by the activation of an adaptive immune response which targets neural antigens. Currently, the role of an innate immune in the development of the lesions in MS has remained unclear. We explore the potential cellular elements of the innate immune system and in particular glial cells, which are likely candidates in inducing the specific pathological picture that is evident in MS. Activated microglia and the release of molecules which are detrimental to oligodendrocyte have been suggested as mechanisms by which innate immunity causes demyelination in MS. However a microglia/macrophage centric model does not explain the specificity of lesion development in MS. We propose that activation pathways of receptors of the innate immune system present on oligodendrocytes and astrocytes rather than microglia are central to the pathogenesis of demyelination seen in MS.