Potential triggers of MS

Differential transcriptomic changes in the central nervous system and urinary bladders of mice infected with a coronavirus

Multiple sclerosis (MS) often leads to the development of neurogenic lower urinary tract symptoms (LUTS). We previously characterized neurogenic bladder dysfunction in a mouse model of MS induced by a coronavirus, mouse hepatitis virus (MHV). The aim of the study was to identify genes and pathways linking neuroinflammation in the central nervous system with urinary bladder (UB) dysfunction to enhance our understanding of the mechanisms underlying LUTS in demyelinating diseases. Adult C57BL/6 male mice (N = 12) received either an intracranial injection of MHV (coronavirus-induced encephalomyelitis, CIE group), or sterile saline (control group). Spinal cord (SC) and urinary bladders (UB) were collected from CIE mice at 1 wk and 4 wks, followed by RNA isolation and NanoString nCounter Neuroinflammation assay. Transcriptome analysis of SC identified a significantly changed expression of >150 genes in CIE mice known to regulate astrocyte, microglia and oligodendrocyte functions, neuroinflammation and immune responses. Two genes were significantly upregulated (Ttr and Ms4a4a), and two were downregulated (Asb2 and Myct1) only in the UB of CIE mice. Siglec1 and Zbp1 were the only genes significantly upregulated in both tissues, suggesting a common transcriptomic link between neuroinflammation in the CNS and neurogenic changes in the UB of CIE mice.

Investigating the disordered regions (MoRFs, SLiMs and LCRs) and functions of mimicry proteins/peptides in silico

Microbial mimicry of the host proteins/peptides can elicit host auto-reactive T- or B-cells resulting in autoimmune disease(s). Since intrinsically disordered protein regions (IDPRs) are involved in several host cell signaling and PPI networks, molecular mimicry of the IDPRs can help the pathogens in substituting their own proteins in the host cell-signaling and PPI networks and, ultimately hijacking the host cellular machinery. Thus, the present study was conducted to discern the structural disorder and intrinsically disordered protein regions (IDPRs) like, molecular recognition features (MoRFs), short linear motifs (SLiMs), and low complexity regions (LCRs) in the experimentally verified mimicry proteins and peptides (mimitopes) of bacteria, viruses and host. Also, functional characteristics of the mimicry proteins were studied in silico. Our results indicated that 78% of the bacterial host mimicry proteins and 45% of the bacterial host mimitopes were moderately/highly disordered while, 73% of the viral host mimicry proteins and 31% of the viral host mimitopes were moderately/highly disordered. Among the pathogens, 27% of the bacterial mimicry proteins and 13% of the bacterial mimitopes were moderately/highly disordered while, 53% of the viral mimicry proteins and 21% of the viral mimitopes were moderately/highly disordered. Though IDPR were frequent in host, bacterial and viral mimicry proteins, only a few mimitopes overlapped with the IDPRs like, MoRFs, SLiMs and LCRs. This suggests that most of the microbes cannot use molecular mimicry to modulate the host PPIs and hijack the host cell machinery. Functional analyses indicated that most of the pathogens exhibited mimicry with the host proteins involved in ion binding and signaling pathways. This is the first report on the disordered regions and functional aspects of experimentally proven host and microbial mimicry proteins.

Complement as a powerful "influencer" in the brain during development, adulthood and neurological disorders

The complement system was long considered as only a powerful effector arm of the immune system that, while critically protective, could lead to inflammation and cell death if overactivated, even in the central nervous system (CNS). However, in the past decade it has been recognized as playing critical roles in key physiological processes in the CNS, including neurogenesis and synaptic remodeling in the developing and adult brain. Inherent in these processes are the interactions with cells in the brain, and the cascade of interactions and functional consequences that ensue. As a result, investigations of therapeutic approaches for both suppressing excessive complement driven neurotoxicity and aberrant sculpting of neuronal circuits, require broad (and deep) knowledge of the functional activities of multiple components of this highly evolved and regulated system to avoid unintended negative consequences in the clinic. Advances in basic science are beginning to provide a roadmap for translation to therapeutics, with both small molecule and biologics. Here, we present examples of the critical roles of proper complement function in the development and sculpting of the nervous system, and in enabling rapid protection from infection and clearance of dying cells. Microglia are highlighted as important command centers that integrate signals from the complement system and other innate sensors that are programed to provide support and protection, but that direct detrimental responses to aberrant activation and/or regulation of the system. Finally, we present promising research areas that may lead to effective and precision strategies for complement targeted interventions to promote neurological health.

Peripheral viral challenge increases c-fos level in cerebral neurons

Peripheral viral infection can substantially alter brain function. We have previously shown that intraperitoneal (i.p.) injection of a viral mimetic, polyinosinic-polycytidylic acid (PIC), engenders hyperexcitability of cerebral neurons. Because neuronal activity is invariably associated with their expression of the Cfos gene, the present study was undertaken to determine whether PIC challenge also increases neuronal c-fos protein level. Female C57BL/6 mice were i.p. injected with PIC, and neuronal c-fos was analyzed in the motor cortex by immunohistochemistry. PIC challenge instigated a robust increase in the number of c-fos-positive neurons. This increase reached approximately tenfold over control at 24 h. Also, the c-fos staining intensity of individual neurons increased. AMG-487, a specific inhibitor of the chemokine receptor CXCR3, profoundly attenuated the accumulation of neuronal c-fos, indicating the activation of CXCL10/CXCR3 axis as the trigger of the process. Together, these results show that the accumulation of c-fos is a viable readout to assess the response of cerebral neurons to peripheral PIC challenge, and to elucidate the underlying molecular mechanisms.

COVID-19: dealing with a potential risk factor for chronic neurological disorders

SARS-CoV2 infection is responsible for a complex clinical syndrome, named Coronavirus Disease 2019 (COVID-19), whose main consequences are severe pneumonia and acute respiratory distress syndrome. Occurrence of acute and subacute neurological manifestations (encephalitis, stroke, headache, seizures, Guillain-Barrè syndrome) is increasingly reported in patients with COVID-19. Moreover, SARS-CoV2 immunopathology and tissue colonization in the gut and the central nervous system, and the systemic inflammatory response during COVID-19 may potentially trigger chronic autoimmune and neurodegenerative disorders. Specifically, Parkinson's disease, multiple sclerosis and narcolepsy present several pathogenic mechanisms that can be hypothetically initiated by SARS-CoV2 infection in susceptible individuals. In this short narrative review, we summarize the clinical evidence supporting the rationale for investigating SARS-CoV2 infection as risk factor for these neurological disorders, and suggest the opportunity to perform in the future SARS-CoV2 serology when diagnosing these disorders.

PART 2: Mouse models for multiple sclerosis research

Lower urinary tract symptoms and dysfunction (LUTS/LUTD) contribute to loss of quality of life, morbidity, and need for medical intervention in most patients with multiple sclerosis (MS). Although MS is an inflammatory neurodegenerative disease, clinical manifestations including continence control disorders have traditionally been attributed to the loss of neural signaling due to neurodegeneration. Clinical approaches to MS-LUTS/LUTD have focused on addressing symptoms in the context of urodynamic dysfunctions as pathophysiologic understandings are incomplete. The mouse model provides a useful research platform for discovery of more detailed molecular, cellular, and tissue-level knowledge of the disease and its clinical manifestations. The aim of this two-part review is to provide a state-of-the-art update on the use of the mouse model for MS research, with a focus on lower urinary tract symptoms. Part I presents a summary of current understanding of MS pathophysiology, the impact on lower urinary tract symptoms, and briefly introduces the types of mouse models available to study MS. Part II presents the common animal models that are currently available to study MS, their mechanism, relevance to MS-LUTS/LUTD and their urinary pathophysiology, advantages and disadvantages.

Viral mouse models used to study multiple sclerosis: past and present

Multiple sclerosis (MS) is a common inflammatory demyelinating disease of the central nervous system. Although the etiology of MS is unknown, genetics and environmental factors, such as infections, play a role. Viral infections of mice have been used as model systems to study this demyelinating disease of humans. Three viruses that have long been studied in this capacity are Theiler’s murine encephalomyelitis virus, mouse hepatitis virus, and Semliki Forest virus. This review describes the viruses themselves, the infection process, the disease caused by infection and its accompanying pathology, and the model systems and their usefulness in studying MS.

Neuronal CXCL10/CXCR3 Axis Mediates the Induction of Cerebral Hyperexcitability by Peripheral Viral Challenge

Peripheral infections can potently exacerbate neuropathological conditions, though the underlying mechanisms are poorly understood. We have previously demonstrated that intraperitoneal (i.p.) injection of a viral mimetic, polyinosinic-polycytidylic acid (PIC) induces a robust generation of CXCL10 chemokine in the hippocampus. The hippocampus also features hyperexcitability of neuronal circuits following PIC challenge. The present study was undertaken to determine the role of CXCL10 in mediating the development of hyperexcitability in response to PIC challenge. Briefly, young female C57BL/6 mice were i.p. injected with PIC, and after 24 h, the brains were analyzed by confocal microscopy. CXCL10 staining of neuronal perikarya and a less intense staining of the neuropil was observed in the hippocampus and cortex. CXCL10 staining was also evident in a subpopulation of astrocytes, whereas microglia were CXCL10 negative. CXCR3, the cognate receptor of CXCL10 was present exclusively on neurons, indicating that the CXCL10/CXCR3 axis operates through an autocrine/paracrine neuronal signaling. Blocking cerebral CXCR3 through intracerebroventricular injection of a specific inhibitor, AMG487, abrogated PIC challenge-induced increase in basal synaptic transmission and long-term potentiation (LTP), as well as the reduction of paired-pulse facilitation (PPF), in the hippocampus. The PIC-mediated abolishment of hippocampal long-term depression (LTD) was also restored after administration of AMG487. Moreover, CXCR3 inhibition attenuated seizure hypersensitivity induced by PIC challenge. The efficacy of AMG487 strongly strengthens the notion that CXCL10/CXCR3 axis mediates the induction of cerebral hyperexcitability by PIC challenge.

An evaluation of HHV-6 as an etiologic agent in Hodgkin lymphoma and brain cancer using IARC criteria for oncogenicity

BACKGROUND

Human herpesvirus-6 (HHV-6) is a ubiquitous double-stranded DNA virus that can cause roseola infantum, encephalitis, and seizure disorders. Several studies have shown an association between HHV-6 and cancer but confirmation of an etiologic role is lacking. We reviewed the criteria for viral causation of cancer used by The International Agency for Research on Cancer (IARC) for six oncogenic viruses and applied criteria to published reports of HHV-6 and its association with Hodgkin lymphoma and brain tumors.

METHODS

Our major criteria for oncogenicity were finding evidence of the virus in every tumor cell and prevention of the tumor by an antiviral vaccine. Our six minor criteria included: 1) suggestive serologic correlation, such as higher virus antibody levels in cases compared to controls; 2) evidence of the virus in some but not all tumor cells, and 3) time space clustering. We focused on Epstein-Barr virus (EBV) as the primary virus for comparison as HHV-6 and EBV are both Herpesviridae, ubiquitous infections, and EBV is well-accepted as a human oncovirus. Particular attention was given to Hodgkin lymphoma (HL) and brain cancer as these malignancies have been the most studied.

RESULTS

No studies reported HHV-6 satisfying either of the major criteria for oncogenicity. Of the minor criteria used by IARC, serologic studies have been paramount in supporting EBV as an oncogenic agent in all EBV-associated tumors, but not for HHV-6 in HL or brain cancer. Clustering of cases was suggestive for both HL and brain cancer and medical intervention suggested by longer survival in patients treated with antiviral agents was reported for brain cancer.

CONCLUSION

There is insufficient evidence to indicate HHV-6 is an etiologic agent with respect to HL and brain cancers. We suggest that methods demonstrating EBV oncogenicity be applied to HHV-6. It is important that one study has found HHV-6 in all cancer cells in oral cancer in a region with elevated HHV-6 antibodies and therefore HHV-6 can still be considered a possible human oncogenic virus.

Peripheral viral challenge exacerbates experimental autoimmune encephalomyelitis

Peripheral viral infections are potent triggers of exacerbation in multiple sclerosis (MS). Here, we used a preclinical model of MS, the experimental autoimmune encephalomyelitis (EAE) to corroborate this comorbidity in an experimental setting. EAE was induced by immunization of mice with MOG peptide, and paralysis was scored using a 5-point scale. At the onset of the chronic phase of the disease (Days 42-58 after MOG injection) the animals were divided into low responders (LR) and high responders (HR) with the mean score of 1.5 and 2.5, respectively. The acute phase response (APR) was induced by intraperitoneal injections of a viral mimetic, polyinosinic-polycytidylic acid (PIC). Two daily injections were performed on Days 42 and 44 (PIC_42,44 challenge) and on Days 54, 55 and 56 (PIC_54,55,56 challenge). PIC_42,44 challenge had no effect of EAE disease, whereas PIC_54,55,56 challenge rapidly increased paralysis but only in HR group. This exacerbation ultimately led to animal death by Day 58. These results demonstrate that antiviral APR is a potent exacerbator of EAE, and that this activity directly correlates with the severity of the disease. This in turn, indicates that antiviral APR might play a pivot role in linking peripheral viral infections with MS exacerbations.

Innate Immune Responses and Viral-Induced Neurologic Disease

Multiple sclerosis (MS) is a disease of the central nervous system (CNS) characterized by chronic neuroinflammation, axonal damage, and demyelination. Cellular components of the adaptive immune response are viewed as important in initiating formation of demyelinating lesions in MS patients. This notion is supported by preclinical animal models, genome-wide association studies (GWAS), as well as approved disease modifying therapies (DMTs) that suppress clinical relapse and are designed to impede infiltration of activated lymphocytes into the CNS. Nonetheless, emerging evidence demonstrates that the innate immune response e.g., neutrophils can amplify white matter damage through a variety of different mechanisms. Indeed, using a model of coronavirus-induced neurologic disease, we have demonstrated that sustained neutrophil infiltration into the CNS of infected animals correlates with increased demyelination. This brief review highlights recent evidence arguing that targeting the innate immune response may offer new therapeutic avenues for treatment of demyelinating disease including MS.

Herpesvirus trigger accelerates neuroinflammation in a nonhuman primate model of multiple sclerosis

Pathogens, particularly human herpesviruses (HHVs), are implicated as triggers of disease onset/progression in multiple sclerosis (MS) and other neuroinflammatory disorders. However, the time between viral acquisition in childhood and disease onset in adulthood complicates the study of this association. Using nonhuman primates, we demonstrate that intranasal inoculations with HHV-6A and HHV-6B accelerate an MS-like neuroinflammatory disease, experimental autoimmune encephalomyelitis (EAE). Although animals inoculated intranasally with HHV-6 (virus/EAE marmosets) were asymptomatic, they exhibited significantly accelerated clinical EAE compared with control animals. Expansion of a proinflammatory CD8 subset correlated with post-EAE survival in virus/EAE marmosets, suggesting that a peripheral (viral?) antigen-driven expansion may have occurred post-EAE induction. HHV-6 viral antigen in virus/EAE marmosets was markedly elevated and concentrated in brain lesions, similar to previously reported localizations of HHV-6 in MS brain lesions. Collectively, we demonstrate that asymptomatic intranasal viral acquisition accelerates subsequent neuroinflammation in a nonhuman primate model of MS.

Signaling pathways and therapeutic perspectives related to environmental factors associated with multiple sclerosis

Multiple sclerosis (MS) is an immune-mediated demyelinating disorder of unknown etiology. Both genetic-susceptibility and environment exposures, including vitamin D deficiency, Epstein-Barr viral and Herpesvirus (HHV-6) infections are strongly implicated in the activation of T cells and MS-pathogenesis. Despite precise knowledge of how these factors could be operating alone or in combination to facilitate and aggravate the disease progression, it is clear that prolonged induction of inflammatory molecules and recruitment of other immune cells by the activated T cells results in demyelination and axonal damage. It is imperative to understand the risk factors associated with MS progression and how these factors contribute to disease pathology. Understanding of the underlying mechanisms of what factors triggers activation of T cells to attack myelin antigen are important to strategize therapeutics and therapies against MS. Current review provides a detailed literature to understand the role of both pathogenic and non-pathogenic factors on the impact of MS.

Strain specificities in age-related changes in mechanisms promoting and controlling rat spinal cord damage in experimental autoimmune encephalomyelitis

The study investigated strain specificities in age-related differences in CD8+ T cell- and microglial cell-mediated mechanisms implicated in induction/perpetuation and/or control of neuroinflammation in experimental autoimmune encephalomyelitis (EAE) in Albino Oxford (AO) and Dark Agouti (DA) rats exhibiting age-related changes in the susceptibility to EAE in the opposite direction (increase in relatively resistant AO rats vs decrease in DA rats). In the inductive phase of EAE, the greater number of fully differentiated effector CD8+ T lymphocytes was found in draining lymph nodes (dLNs) from aged rats of both strains than in strain-matched young rats, but this was particularly prominent in AO rats, which exhibited milder EAE of prolonged duration compared with their DA counterparts. Consistently, dLN IFN-γ+ and IL-17+ CD8+ T cell counts were greater in aged AO than in DA rats. Additionally, the magnitudes of myelin basic protein (MBP)-induced rise in the frequency of IFN-γ+ and IL-17+ CD8+ T cells (providing important help to neuroantigen-specific CD4+ T cells in EAE models characterized by clinically mild disease) were greater in dLN cell cultures from aged AO rats. Consistently, the magnitudes of MBP-induced rise in the frequency of both IFN-γ+ and IL-17+ CD8+ T cells were greater in spinal cord mononuclear cell cultures from aged AO rats compared with their DA counterparts. Besides, with aging CD4+CD25+Foxp3+/CD8+CD25+Foxp3+ regulatory T cell ratio changed in spinal cord in the opposite direction. Consequently, in aged AO rats it was shifted towards CD8+CD25+Foxp3+ regulatory T cells (exhibiting lower suppressive capacity) when compared with DA rats. Moreover, the frequency of CX3CR1+ cells among microglia changed with aging and the disease development. In aged rats, in the effector phase of EAE it was lower in AO than in DA rats. This was accompanied by higher frequency of cells expressing IL-1β (whose down-regulation is central for CX3CR1-mediated neuroprotection), but lower that of phagocyting cells among microglia from aged AO compared their DA counterparts. The study indicates the control points linked with strain differences in age-related changes in EAE pathogenesis.

The MHC locus and genetic susceptibility to autoimmune and infectious diseases

In the past 50 years, variants in the major histocompatibility complex (MHC) locus, also known as the human leukocyte antigen (HLA), have been reported as major risk factors for complex diseases. Recent advances, including large genetic screens, imputation, and analyses of non-additive and epistatic effects, have contributed to a better understanding of the shared and specific roles of MHC variants in different diseases. We review these advances and discuss the relationships between MHC variants involved in autoimmune and infectious diseases. Further work in this area will help to distinguish between alternative hypotheses for the role of pathogens in autoimmune disease development.

The MHC locus and genetic susceptibility to autoimmune and infectious diseases

In the past 50 years, variants in the major histocompatibility complex (MHC) locus, also known as the human leukocyte antigen (HLA), have been reported as major risk factors for complex diseases. Recent advances, including large genetic screens, imputation, and analyses of non-additive and epistatic effects, have contributed to a better understanding of the shared and specific roles of MHC variants in different diseases. We review these advances and discuss the relationships between MHC variants involved in autoimmune and infectious diseases. Further work in this area will help to distinguish between alternative hypotheses for the role of pathogens in autoimmune disease development.

Theiler's murine encephalomyelitis virus infection of SJL/J and C57BL/6J mice: Models for multiple sclerosis and epilepsy

Mouse models are great tools to study the mechanisms of disease development. Theiler's murine encephalomyelitis virus is used in two distinct viral infection mouse models to study the human diseases multiple sclerosis (MS) and epilepsy. Intracerebral (i.c.) infection of the SJL/J mouse strain results in persistent viral infection of the central nervous system and a MS-like disease, while i.c. infection of the C57BL/6J mouse strain results in acute seizures and epilepsy. Our understanding of how the immune system contributes to the development of two disparate diseases caused by the same virus is presented.

HTLV-1, Immune Response and Autoimmunity

Human T-lymphotropic virus type-1 (HTLV-1) infection is associated with adult T-cell leukemia/lymphoma (ATL). Tropical spastic paraparesis/HTLV-1-associated myelopathy (PET/HAM) is involved in the development of autoimmune diseases including Rheumatoid Arthritis (RA), Systemic Lupus Erythematosus (SLE), and Sjögren's Syndrome (SS). The development of HTLV-1-driven autoimmunity is hypothesized to rely on molecular mimicry, because virus-like particles can trigger an inflammatory response. However, HTLV-1 modifies the behavior of CD4⁺ T cells on infection and alters their cytokine production. A previous study showed that in patients infected with HTLV-1, the activity of regulatory CD4⁺ T cells and their consequent expression of inflammatory and anti-inflammatory cytokines are altered. In this review, we discuss the mechanisms underlying changes in cytokine release leading to the loss of tolerance and development of autoimmunity.

Multiple sclerosis: autoimmunity and viruses

PURPOSE OF REVIEW

This review will explore two new aspects of the involvement of viruses in multiple sclerosis pathogenesis. The first aspect is the complex interactions between viruses. The second aspect is the proposal of a mechanism by which autoreactive T cells are able to escape thymic selection and potentially recognize self and a pathogen.

RECENT FINDINGS

With regard to viruses, recent work has demonstrated that one virus may enhance the replication of another virus, potentially leading to an increase in inflammation and disease progression. Also, interactions between human endogenous retroviruses, which likely do not replicate, and certain herpes viruses, may also play a role in disease pathogenesis. Mechanistically, T cells expressing dual T-cell receptors would be able to recognize self and a foreign antigen specifically. Therefore, human endogenous retroviruses potentially play a role in multiple sclerosis pathogenesis, and both interactions between multiple viruses and autoreactive CD8(+) T cells with dual T-cell receptors may play a role in the pathogenesis of the disease.

SUMMARY

The complex interactions between multiple viral infections, either within the central nervous system or in the periphery, and the host immune response to viral infection may be such that a variety of viral specificities result in the activation of T cells that recognize self and induce multiple sclerosis. Therefore, it is unlikely that any one microbe will be determined to be the causative agent of multiple sclerosis as reflected by the number of potential triggering mechanisms of the disease.

Role of pathogens in multiple sclerosis

Multiple sclerosis (MS) is an inflammatory demyelinating autoimmune disease of the central nervous system (CNS). Although the etiology of MS is unknown, genetic and environmental factors play a role. Infectious pathogens are the likely environmental factors involved in the development of MS. Pathogens associated with the development or exacerbation of MS include bacteria, such as Mycoplasma pneumoniae and Chlamydia pneumoniae, the Staphylococcus aureus-produced enterotoxins that function as superantigens, viruses of the herpes virus (Epstein-Barr virus and human herpesvirus 6) and human endogenous retrovirus (HERV) families and the protozoa Acanthamoeba castellanii. Evidence, from studies with humans and animal models, supporting the association of these various pathogens with the development and/or exacerbation of MS will be discussed along with the potential mechanisms including molecular mimicry, epitope spreading and bystander activation. In contrast, infection with certain parasites such as helminthes (Schistosoma mansoni, Fasciola hepatica, Hymenolepis nana, Trichuris trichiura, Ascaris lumbricoides, Strongyloides stercolaris, Enterobius vermicularis) appears to protect against the development or exacerbation of MS. Evidence supporting the ability of parasitic infections to protect against disease will be discussed along with a brief summary of a recent Phase I clinical trial testing the ability of Trichuris suis ova treatment to improve the clinical course of MS. A complex interaction between the CNS (including the blood-brain barrier), multiple infections with various infectious agents (occurring in the periphery or within the CNS), and the immune response to those various infections may have to be deciphered before the etiology of MS can be fully understood.

Epstein-Barr virus in systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis—association and causation

Epidemiological data suggest that the Epstein-Barr virus (EBV) is associated with several autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis. However, it is not clear whether EBV plays a role in the pathogenesis of these diseases, and if so, by which mechanisms the virus may contribute. In this review, we discuss possible viral and immunological mechanisms that might explain associations between EBV and autoimmune diseases and whether these associations represent causes or effects of inflammation and autoimmunity.

Possible role of interleukin-17 in a prime/challenge model of multiple sclerosis

No one single pathogen has been identified as the causative agent of multiple sclerosis (MS). Alternately, the likelihood of an autoimmune event may be nonspecifically enhanced by different infectious agents. In a novel animal model of MS, SJL/J mice primed through infection with a recombinant vaccinia virus (VV) encoding myelin proteolipid protein (PLP) (VV(PLP)) were susceptible to a central nervous system (CNS) inflammatory disease following administration of a nonspecific immunostimulant [complete Freund's adjuvant (CFA) plus Bordetella pertussis (BP)]. Mononuclear cells isolated from the brains, but not the spleens, of VV(PLP)-primed CFA/BP challenged mice produced interleukin (IL)-17 and interferon-γ and transferred a CNS inflammatory disease to naïve SJL/J mice. Administration of curdlan, a T helper 17 cell inducer, unexpectedly resulted in less severe clinical and histological signs of disease, compared to CFA/BP challenged mice, despite the induction of IL-17 in the periphery. Further examination of the VV(PLP)-prime CFA/BP challenge model may suggest new mechanisms for how different pathogens associated with MS can protect or enhance disease.

Molecular mimicry as a mechanism of autoimmune disease

A variety of mechanisms have been suggested as the means by which infections can initiate and/or exacerbate autoimmune diseases. One mechanism is molecular mimicry, where a foreign antigen shares sequence or structural similarities with self-antigens. Molecular mimicry has typically been characterized on an antibody or T cell level. However, structural relatedness between pathogen and self does not account for T cell activation in a number of autoimmune diseases. A proposed mechanism that could have been misinterpreted for molecular mimicry is the expression of dual T cell receptors (TCR) on a single T cell. These T cells have dual reactivity to both foreign and self-antigens leaving the host vulnerable to foreign insults capable of triggering an autoimmune response. In this review, we briefly discuss what is known about molecular mimicry followed by a discussion of the current understanding of dual TCRs. Finally, we discuss three mechanisms, including molecular mimicry, dual TCRs, and chimeric TCRs, by which dual reactivity of the T cell may play a role in autoimmune diseases.

Epstein-Barr virus stimulates torque teno virus replication: a possible relationship to multiple sclerosis

Viral infections have been implicated in the pathogenesis of multiple sclerosis. Epstein-Barr virus (EBV) has frequently been investigated as a possible candidate and torque teno virus (TTV) has also been discussed in this context. Nevertheless, mechanistic aspects remain unresolved. We report viral replication, as measured by genome amplification, as well as quantitative PCR of two TTV-HD14 isolates isolated from multiple sclerosis brain in a series of EBV-positive and -negative lymphoblastoid and Burkitt's lymphoma cell lines. Our results demonstrate the replication of both transfected TTV genomes up to day 21 post transfection in all the evaluated cell lines. Quantitative amplification indicates statistically significant enhanced TTV replication in the EBV-positive cell lines, including the EBV-converted BJAB line, in comparison to the EBV-negative Burkitt's lymphoma cell line BJAB. This suggests a helper effect of EBV infections in the replication of TTV. The present study provides information on a possible interaction of EBV and TTV in the etiology and progression of multiple sclerosis.

Antiviral CD8⁺ T cells cause an experimental autoimmune encephalomyelitis-like disease in naive mice

Major histocompatibility complex class I-restricted CD8(+) cytotoxic T lymphocytes are involved in the pathogenesis of multiple sclerosis (MS) and both autoimmune, experimental autoimmune encephalomyelitis, and viral, Theiler's murine encephalomyelitis virus (TMEV) infection, animal models of MS. Following TMEV infection, certain T cell hybridomas, generated from cloned TMEV-induced CD8(+) T cells, were able to produce clinical signs of disease (flaccid hind limb paralysis) upon adoptive transfer into naive mice. Dual T cell receptors (TCR) are present on the surface of these cells as both Vβ3 and Vβ6 were detected by polymerase chain reaction (PCR) screening and flow cytometry and multiple Vα mRNAs were detected by PCR screening. This is the first demonstration of antiviral CD8(+) T cells having more than one TCR initiating an autoimmune disease in the natural host of the virus. We hypothesize that this is a potential mechanism for virus-induced autoimmune disease initiated by CD8(+) T cells.

Human T cell expansion and experimental autoimmune encephalomyelitis inhibited by Lenaldekar, a small molecule discovered in a zebrafish screen

Immune-mediated diseases [multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE)] are driven by proliferating, highly activated autoreactive T-cells that are unresponsive to in vivo immunoregulatory mechanisms. The compound Lenaldekar (LDK) was identified in a zebrafish screen by inhibiting T-cell expansion. By monitoring mitogen- and antigen-driven proliferation, we found that LDK inhibited human and murine T-cell expansion in a non-cytolytic manner. This suppressive activity directly correlated with the degree of activation/proliferation of the T-cells. In testing LDK in an EAE model of MS, exacerbations were suppressed in treated animals. Therefore, LDK represents a novel therapeutic approach to T-cell-mediated autoimmune diseases.

Combinatorial antibody library from multiple sclerosis patients reveals antibodies that cross-react with myelin basic protein and EBV antigen

Multiple sclerosis (MS) is a widespread neurodegenerative autoimmune disease with unknown etiology. It is increasingly evident that, together with pathogenic T cells, autoreactive B cells are among the major players in MS development. The analysis of myelin neuroantigen-specific antibody repertoires and their possible cross-reactivity against environmental antigens, including viral proteins, could shed light on the mechanism of MS induction and progression. A phage display library of single-chain variable fragments (scFvs) was constructed from blood lymphocytes of patients with MS as a potential source of representative MS autoantibodies. Structural alignment of 13 clones selected toward myelin basic protein (MBP), one of the major myelin antigens, showed high homology within variable regions with cerebrospinal fluid MS-associated antibodies as well as with antibodies toward Epstein-Barr latent membrane protein 1 (LMP1). Three scFv clones showed pronounced specificity to MBP fragments 65-92 and 130-156, similar to the serum MS antibodies. One of these clones, designated E2, in both scFv and full-size human antibody constructs, was shown to react with both MBP and LMP1 proteins in vitro, suggesting natural cross-reactivity. Thus, antibodies induced against LMP1 during Epstein-Barr virus infection might act as inflammatory trigger by reacting with MBP, suggesting molecular mimicry in the mechanism of MS pathogenesis.

Experimental autoimmune encephalomyelitis as a testing paradigm for adjuvants and vaccines

Experimental autoimmune encephalomyelitis (EAE) is an experimental model for multiple sclerosis. EAE can be induced by inoculation with central nervous system (CNS) proteins or peptides emulsified in complete Freund's adjuvant. Protection from EAE, enhancement of EAE or subclinical priming for EAE can occur as a result of either live viral infection or DNA immunization with molecular mimics of CNS proteins or peptides. Here we review the published data describing modulation of EAE through administration of various CNS proteins/peptides introduced via live virus or plasmid DNA and modulation of EAE through choice of adjuvant (immunostimulating agents).

Studies in the modulation of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE), an experimental model for multiple sclerosis, can be induced through inoculation with several different central nervous system (CNS) proteins or peptides. Modulation of EAE, resulting in either protection from EAE or enhancement of EAE, can also be accomplished through either vaccination or DNA immunization with molecular mimics of self-CNS proteins. Previously published data on this method of EAE modulation will be reviewed. New data is presented, which demonstrates that EAE can also be modulated through the administration of the beta-(1,3)-D-glucan, curdlan. Dendritic cells stimulated by curdlan are involved in the differentiation of the interleukin-17 producing subset of CD4(+) T cells that are recognized effector cells in EAE. Using two different systems to study the effects of curdlan on EAE, it was found that curdlan increased the incidence of EAE and/or the severity of the disease course.