Infections in MS: An innate immunity perspective

Potential clinical implications of molecular mimicry-induced autoimmunity

BACKGROUND

Molecular mimicry is hypothesized to be a mechanism by which autoimmune diseases are triggered. It refers to sequence or structural homology between foreign antigens and self-antigens, which can activate cross-reactive lymphocytes that attack host tissues. Elucidating the role of molecular mimicry in human autoimmunity could have important clinical implications.

OBJECTIVE

To review evidence for the role of molecular mimicry in major autoimmune diseases and discuss potential clinical implications.

METHODS

Comprehensive literature review of clinical trials, observational studies, animal models, and immunology studies on molecular mimicry in multiple sclerosis, type 1 diabetes, rheumatoid arthritis, lupus, Guillain-Barre syndrome, autoimmune myocarditis, and primary biliary cirrhosis published from 2000-2023.

RESULTS

Substantial indirect evidence supports molecular mimicry as a contributor to loss of self-tolerance in several autoimmune conditions. Proposed microbial triggers include Epstein-Barr virus, coxsackievirus, Campylobacter jejuni, and bacterial commensals. Key mechanisms involve cross-reactive T cells and autoantibodies induced by epitope homology between microbial and self-antigens. Perpetuation of autoimmunity involves epitope spreading, inflammatory mediators, and genetic factors.

CONCLUSIONS

Molecular mimicry plausibly explains initial stages of autoimmune pathogenesis induced by infection or microbiota disturbances. Understanding mimicry antigens and pathways could enable improved prediction, monitoring, and antigen-specific immunotherapy for autoimmune disorders. However, definitive proof of causation in humans remains limited. Further research should focus on establishing clinical evidence and utility.

Interferon Beta-1a versus Glatiramer Acetate: Changes of Innate Immunity in a Group of Women with Multiple Sclerosis

INTRODUCTION

Multiple sclerosis (MS) is a chronic inflammatory autoimmune demyelinating disease that secondarily leads to axonal loss and associated brain atrophy. Disease-modifying drugs (DMDs) have previously been studied for their ability to affect specific immunity. This study investigates the effect of interferon beta-1a (INF) and glatiramer acetate (GA) administration on changes in innate immunity cell populations.

METHODS

Sixty Caucasian female patients with relapsing-remitting MS undergo blood sample testing for 15 blood parameters at baseline, 1 month, 3 months, and 6 months after treatment by GA or IFN (started as their first-line DMD).

RESULTS

A statistically significant difference in the change after 6 months was found in the parameter monocytes (relative count) in the group of patients treated with IFN. The median increase was 27.8%. Changes in many of the other 15 parameters studied were 10-20%.

CONCLUSION

Innate immunity has long been neglected in MS immunopathology. The findings suggest that IFN treatment may modulate the immune response in MS by affecting monocyte function and may provide insight into the mechanisms of action of IFN in MS.

Glial cells and neurologic autoimmune disorders

Neurologic autoimmune disorders affect people's physical and mental health seriously. Glial cells, as an important part of the nervous system, play a vital role in the occurrence of neurologic autoimmune disorders. Glial cells can be hyperactivated in the presence of autoantibodies or pathological changes, to influence neurologic autoimmune disorders. This review is mainly focused on the roles of glial cells in neurologic autoimmune disorders and the influence of autoantibodies produced by autoimmune disorders on glial cells. We speculate that the possibility of glial cells might be a novel way for the investigation and therapy of neurologic autoimmune disorders.

Oligodendrocytes and Microglia: Key Players in Myelin Development, Damage and Repair

Oligodendrocytes, the myelin-making cells of the CNS, regulate the complex process of myelination under physiological and pathological conditions, significantly aided by other glial cell types such as microglia, the brain-resident, macrophage-like innate immune cells. In this review, we summarize how oligodendrocytes orchestrate myelination, and especially myelin repair after damage, and present novel aspects of oligodendroglial functions. We emphasize the contribution of microglia in the generation and regeneration of myelin by discussing their beneficial and detrimental roles, especially in remyelination, underlining the cellular and molecular components involved. Finally, we present recent findings towards human stem cell-derived preclinical models for the study of microglia in human pathologies and on the role of microbiome on glial cell functions.

The expression profile of virus-recognizing toll-like receptors in natural killer cells of Cypriot multiple sclerosis patients

Objective

The exact aetiology of multiple sclerosis (MS) remains elusive, although several environmental and genetic risk factors have been implicated to varying degrees. Among the environmental risk factors, viral infections have been suggested as strong candidates contributing to MS pathology/progression. Viral recognition and control are largely tasked to the NK cells via TLR recognition and various cytotoxic and immunoregulatory functions. Additionally, the complex roles of different TLRs in MS pathology are highlighted in multiple, often contradictory, studies. The present work aims to analyse the TLR expression profile of NK cells isolated from MS patients. Highly purified CD56⁺CD3⁻ NK cells isolated from peripheral blood of MS patients (n = 19) and healthy controls (n = 20) were analysed via flow cytometry for their expression of viral antigen-recognizing TLRs (TLR2, TLR3, TLR7, and TLR9).

Results

No difference was noted in TLR expression between MS patients and healthy controls. These results aim to supplement previous findings which study expressional or functional differences in TLRs present in various subsets of the immune system in MS, thus aiding in a better understanding of MS as a complex multifaceted disease.

Beneficial Roles of Microglia and Growth Factors in MS, a Brief Review

Microglia are the brain resident immune cells; they can produce a large variety of growth factors (GFs) to prevent neuronal damages and promote recovery. In neurodegenerative diseases, microglia can play both benefic and deleterious roles, depending on different factors and disease context. In multiple sclerosis, microglia are involved in both demyelination (DM) and remyelination (RM) processes. Recent studies suggest a beneficial role of microglia in regenerative processes. These include the regenerative development of myelin after DM. This review gives an overlook of how microglia and GFs can influence the RM properties.

Synergistic Activation of Toll-Like and NOD Receptors by Complementary Antigens as Facilitators of Autoimmune Disease: Review, Model and Novel Predictions

Persistent activation of toll-like receptors (TLR) and nucleotide-binding oligomerization domain-containing proteins (NOD) in the innate immune system is one necessary driver of autoimmune disease (AD), but its mechanism remains obscure. This study compares and contrasts TLR and NOD activation profiles for four AD (autoimmune myocarditis, myasthenia gravis, multiple sclerosis and rheumatoid arthritis) and their animal models. The failure of current AD theories to explain the disparate TLR/NOD profiles in AD is reviewed and a novel model is presented that explains innate immune support of persistent chronic inflammation in terms of unique combinations of complementary AD-specific antigens stimulating synergistic TLRs and/or NODs. The potential explanatory power of the model is explored through testable, novel predictions concerning TLR- and NOD-related AD animal models and therapies.

The endotoxin hypothesis of neurodegeneration

The endotoxin hypothesis of neurodegeneration is the hypothesis that endotoxin causes or contributes to neurodegeneration. Endotoxin is a lipopolysaccharide (LPS), constituting much of the outer membrane of gram-negative bacteria, present at high concentrations in gut, gums and skin and in other tissue during bacterial infection. Blood plasma levels of endotoxin are normally low, but are elevated during infections, gut inflammation, gum disease and neurodegenerative disease. Adding endotoxin at such levels to blood of healthy humans induces systemic inflammation and brain microglial activation. Adding high levels of endotoxin to the blood or body of rodents induces microglial activation, priming and/or tolerance, memory deficits and loss of brain synapses and neurons. Endotoxin promotes amyloid β and tau aggregation and neuropathology, suggesting the possibility that endotoxin synergises with different aggregable proteins to give different neurodegenerative diseases. Blood and brain endotoxin levels are elevated in Alzheimer's disease, which is accelerated by systemic infections, including gum disease. Endotoxin binds directly to APOE, and the APOE4 variant both sensitises to endotoxin and predisposes to Alzheimer's disease. Intestinal permeability increases early in Parkinson's disease, and injection of endotoxin into mice induces α-synuclein production and aggregation, as well as loss of dopaminergic neurons in the substantia nigra. The gut microbiome changes in Parkinson's disease, and changing the endotoxin-producing bacterial species can affect the disease in patients and mouse models. Blood endotoxin is elevated in amyotrophic lateral sclerosis, and endotoxin promotes TDP-43 aggregation and neuropathology. Peripheral diseases that elevate blood endotoxin, such as sepsis, AIDS and liver failure, also result in neurodegeneration. Endotoxin directly and indirectly activates microglia that damage neurons via nitric oxide, oxidants and cytokines, and by phagocytosis of synapses and neurons. The endotoxin hypothesis is unproven, but if correct, then neurodegeneration may be reduced by decreasing endotoxin levels or endotoxin-induced neuroinflammation.

Gliotoxin Aggravates Experimental Autoimmune Encephalomyelitis by Triggering Neuroinflammation

Gliotoxin (GTX) is the major and the most potent mycotoxin that is secreted by Aspergillus fumigatus, which is capable of injuring and killing microglial cells, astrocytes, and oligodendrocytes. During the last years, studies with patients and experimental models of multiple sclerosis (MS), which is an autoimmune disease of the central nervous system (CNS), suggested that fungal infections are among the possible initiators or aggravators of this pathology. The deleterious effect can occur through a direct interaction of the fungus with the CNS or by the toxin release from a non-neurological site. In the present work, we investigated the effect of GTX on experimental autoimmune encephalomyelitis (EAE) development. Female C57BL/6 mice were immunized with myelin oligodendrocyte glycoprotein and then intraperitoneally injected with three doses of GTX (1 mg/kg b.w., each) on days 4, 7, and 10. GTX aggravated clinical symptoms of the disease in a dose-dependent way and this outcome was concomitant with an increased neuroinflammation. CNS analyses revealed that GTX locally increased the relative expression of inflammatory genes and the cytokine production. Our results indicate that GTX administered in a non-neuronal site was able to increase neuroinflammation in EAE. Other mycotoxins could also be deleterious to many neurological diseases by similar mechanisms.

Complete sequence analysis of human toll-like receptor 3 gene in natural killer cells of multiple sclerosis patients

BACKGROUND

Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system (CNS) where both environmental and genetic risk factors play a role. Among the environmental risk factors, EBV and HSV infections have been suggested as strong candidates contributing to MS pathology/progression. Viral recognition and control is largely tasked to the NK cells via TLR recognition and various cytotoxic and immunoregulatory functions. The present work aimed to characterize NK cells isolated from MS patients for genetic polymorphisms in the gene encoding for TLR3, as TLR3 in NK cells is important in herpesvirus recognition.

METHODS

Highly purified NK cells isolated from peripheral blood of MS patients (n = 27) and healthy controls (n = 30) were used to sequence all five exons of the TLR3 gene using sanger sequencing. Alignment of the obtained sequences with the wild-type TLR3 sequence was used to identify genetic polymorphisms within the TLR3 gene.

RESULTS

The alignment identified multiple substitution mutations across the five exons of the TLR3 gene (rs116729895, rs3775296, rs377529, rs3775290, rs3775291, rs376735334 and rs73873710). A significant difference was observed in the allele distribution of rs3775291 (Leu412Phe) between MS patients and HC, whereby the minor allele was detected in 38.9% of MS patients versus 11% of HC (Fisher's exact test, p = 0.021).

CONCLUSION

There appears to be a possible association between the TLR3 missense mutation rs3775291 and multiple sclerosis, which might be attributed to changes in the TLR3 functional properties.