Functional activation of myelin-specific T cells by virus-induced molecular mimicry

Sequence similarity between SARS-CoV-2 nucleocapsid and multiple sclerosis-associated proteins provides insight into viral neuropathogenesis following infection

The novel coronavirus SARS-CoV-2 continues to cause death and disease throughout the world, underscoring the necessity of understanding the virus and host immune response. From the start of the pandemic, a prominent pattern of central nervous system (CNS) pathologies, including demyelination, has emerged, suggesting an underlying mechanism of viral mimicry to CNS proteins. We hypothesized that immunodominant epitopes of SARS-CoV-2 share homology with proteins associated with multiple sclerosis (MS). Using PEPMatch, a newly developed bioinformatics package which predicts peptide similarity within specific amino acid mismatching parameters consistent with published MHC binding capacity, we discovered that nucleocapsid protein shares significant overlap with 22 MS-associated proteins, including myelin proteolipid protein (PLP). Further computational evaluation demonstrated that this overlap may have critical implications for T cell responses in MS patients and is likely unique to SARS-CoV-2 among the major human coronaviruses. Our findings substantiate the hypothesis of viral molecular mimicry in the pathogenesis of MS and warrant further experimental exploration.

Endocannabinoid Modulation in Neurodegenerative Diseases: In Pursuit of Certainty

Simple Summary

Neurodegenerative diseases represent an important cause of morbidity and mortality worldwide. Existing therapeutic options are limited and focus mostly on improving symptoms and reducing exacerbations. The endocannabinoid system is involved in the pathophysiology of such disorders, an idea which has been highlighted by recent scientific work. The current work focusses its attention on the importance and implications of this system and its synthetic and natural ligands in disorders such as Alzheimer’s, Parkinson’s, Huntington’s and multiple sclerosis.

Abstract

Neurodegenerative diseases are an increasing cause of global morbidity and mortality. They occur in the central nervous system (CNS) and lead to functional and mental impairment due to loss of neurons. Recent evidence highlights the link between neurodegenerative and inflammatory diseases of the CNS. These are typically associated with several neurological disorders. These diseases have fundamental differences regarding their underlying physiology and clinical manifestations, although there are aspects that overlap. The endocannabinoid system (ECS) is comprised of receptors (type-1 (CB1R) and type-2 (CB2R) cannabinoid-receptors, as well as transient receptor potential vanilloid 1 (TRPV1)), endogenous ligands and enzymes that synthesize and degrade endocannabinoids (ECBs). Recent studies revealed the involvement of the ECS in different pathological aspects of these neurodegenerative disorders. The present review will explore the roles of cannabinoid receptors (CBRs) and pharmacological agents that modulate CBRs or ECS activity with reference to Alzheimer’s Disease (AD), Parkinson’s Disease (PD), Huntington’s Disease (HD) and multiple sclerosis (MS).

Peripheral Nervous System Involvement in Non-Primary Pediatric Cancer: From Neurotoxicity to Possible Etiologies

Peripheral neuropathy is a well described complication in children with cancer. Oncologists are generally well aware of the toxicity of the main agents, but fear the side effects of new drugs. As chemotherapeutic agents have been correlated with the activation of the immune system such as in Chemotherapy Induced Peripheral Neuropathy (CIPN), an abnormal response can lead to Autoimmune Peripheral Neuropathy (APN). Although less frequent but more severe, Radiation Induced Peripheral Neuropathy may be related to irreversible peripheral nervous system (PNS). Pediatric cancer patients also have a higher risk of entering a Pediatric Intensive Care Unit for complications related to therapy and disease. Injury to peripheral nerves is cumulative, and frequently, the additional stress of a malignancy and its therapy can unmask a subclinical neuropathy. Emerging risk factors for CIPN include treatment factors such as dose, duration and concurrent medication along with patient factors, namely age and inherited susceptibilities. The recent identification of individual genetic variations has advanced the understanding of physiopathological mechanisms and may direct future treatment approaches. More research is needed on pharmacological agents for the prevention or treatment of the condition as well as rehabilitation interventions, in order to allow for the simultaneous delivery of optimal cancer therapy and the mitigation of toxicity associated with pain and functional impairment. The aim of this paper is to review literature data regarding PNS complications in non-primary pediatric cancer.

Multiple sclerosis: experimental models and reality

One of the most frequent statements, provided in different variations in the introduction of experimental studies on multiple sclerosis (MS), is that "Multiple sclerosis is a demyelinating autoimmune disease and experimental autoimmune encephalomyelitis (EAE) is a suitable model to study its pathogenesis". However, so far, no single experimental model covers the entire spectrum of the clinical, pathological, or immunological features of the disease. Many different models are available, which proved to be highly useful for studying different aspects of inflammation, demyelination, remyelination, and neurodegeneration in the central nervous system. However, the relevance of results from such models for MS pathogenesis has to be critically validated. Current EAE models are mainly based on inflammation, induced by auto-reactive CD4+ T-cells, and these models reflect important aspects of MS. However, pathological data and results from clinical trials in MS indicate that CD8+ T-cells and B-lymphocytes may play an important role in propagating inflammation and tissue damage in established MS. Viral models may reflect key features of MS-like inflammatory demyelination, but are difficult to use due to their very complex pathogenesis, involving direct virus-induced and immune-mediated mechanisms. Furthermore, evidence for a role of viruses in MS pathogenesis is indirect and limited, and an MS-specific virus infection has not been identified so far. Toxic models are highly useful to unravel mechanisms of de- and remyelination, but do not reflect other important aspects of MS pathology and pathogenesis. For all these reasons, it is important to select the right experimental model to answer specific questions in MS research.

During Infection, Theiler's Virions Are Cleaved by Caspases and Disassembled into Pentamers

Infected macrophages in spinal cords of mice persistently infected with Theiler's murine encephalomyelitis virus (TMEV) undergo apoptosis, resulting in restricted virus yields, as do infected macrophages in culture. Apoptosis of murine macrophages in culture occurs via the intrinsic pathway later in infection (>10 h postinfection [p.i.]) after maximal virus titers (150 to 200 PFU/cell) have been reached, with loss of most infectious virus (<5 PFU/cell) by 20 to 24 h p.i. Here, we show that BeAn virus RNA replication, translation, polyprotein processing into final protein products, and assembly of protomers and pentamers in infected M1-D macrophages did not differ from those processes in TMEV-infected BHK-21 cells, which undergo necroptosis. However, the initial difference from BHK-21 cell infection was seen at 10 to 12 h p.i., where virions from the 160S peak in sucrose gradients had incompletely processed VP0 (compared to that in infected BHK-21 cells). Thereafter, there was a gradual loss of the 160S virion peak in sucrose gradients, with replacement by a 216S peak that was observed to contain pentamers among lipid debris in negatively stained grids by electron microscopy. After infection or incubation of purified virions with activated caspase-3 in vitro, 13- and 17-kDa capsid peptide fragments were observed and were predicted by algorithms to contain cleavage sites within proteins by cysteine-dependent aspartate-directed proteases. These findings suggest that caspase cleavage of sites in exposed capsid loops of assembled virions occurs contemporaneously with the onset and progression of apoptosis later in the infection.

IMPORTANCE

Theiler's murine encephalomyelitis virus (TMEV) infection in mice results in establishment of virus persistence in the central nervous system and chronic inflammatory demyelinating disease, providing an experimental animal model for multiple sclerosis. Virus persistence takes place primarily in macrophages recruited into the spinal cord that undergo apoptosis and in turn may facilitate viral spread via infected apoptotic blebs. Infection of murine macrophages in culture results in restricted virus yields late in infection. Here it is shown that the early steps of the virus life cycle in infected macrophages in vitro do not differ from these processes in TMEV-infected BHK-21 cells, which undergo necroptosis. However, the findings late in infection suggest that caspases cleave sites in exposed capsid loops and possibly internal sites of assembled virions occurring contemporaneously with onset and progression of apoptosis. Mechanistically, this would explain the dramatic loss in virus yields during TMEV-induced apoptosis and attenuate the virus, enabling persistence.

Depletion of Olig2 in oligodendrocyte progenitor cells infected by Theiler's murine encephalomyelitis virus

Theiler's murine encephalomyelitis virus (TMEV) infects the central nervous system of mice and causes a demyelinating disease that is a model for multiple sclerosis. During the chronic phase of the disease, TMEV persists in oligodendrocytes and macrophages. Lack of remyelination has been attributed to insufficient proliferation and differentiation of oligodendrocyte progenitor cells (OPCs), but the molecular mechanisms remain unknown. Here, we employed pluripotent stem cell technologies to generate pure populations of mouse OPCs to study the temporal and molecular effects of TMEV infection. Global transcriptome analysis of RNA sequencing data revealed that TMEV infection of OPCs caused significant up-regulation of 1926 genes, whereas 1853 genes were significantly down-regulated compared to uninfected cells. Pathway analysis revealed that TMEV disrupted many genes required for OPC growth and maturation. Down-regulation of Olig2, a transcription factor necessary for OPC proliferation, was confirmed by real-time PCR, immunofluorescence microscopy, and western blot analysis. Depletion of Olig2 was not found to be specific to viral strain and did not require expression of the leader (L) protein, which is a multifunctional protein important for persistence, modulation of gene expression, and cell death. These data suggest that direct infection of OPCs by TMEV may inhibit remyelination during the chronic phase of TMEV-induced demyelinating disease.

Mimicry epitope from Ehrlichia canis for interphotoreceptor retinoid-binding protein 201-216 prevents autoimmune uveoretinitis by acting as altered peptide ligand

We report here identification of novel mimicry epitopes for interphotoreceptor retinoid-binding protein (IRBP) 201-216, a candidate ocular antigen that causes experimental autoimmune uveoretinitis (EAU) in A/J mice. One mimicry epitope from Ehrlichia canis (EHC), designated EHC 44-59, induced cross-reactive T cells for IRBP 201-216 capable of producing T helper (Th)1 and Th17 cytokines, but failed to induce EAU in A/J mice. In addition, animals first primed with suboptimal doses of IRBP 201-216 and subsequently immunized with EHC 44-59 did not develop EAU; rather, the mimicry epitope prevented the disease induced by IRBP 201-216. However, alteration in the composition of EHC 44-59 by substituting alanine with valine at position 49, similar to the composition of IRBP 201-216, enabled the mimicry epitope to acquire uveitogenicity. The data provide new insights as to how microbes containing mimicry sequences for retinal antigens can prevent ocular inflammation by acting as naturally occurring altered peptide ligands.

Pediatric acute transverse myelitis overview and differential diagnosis

Acute transverse myelitis is a clinical syndrome affecting the spinal cord, which is characterized by acute onset of motor, sensory, and autonomic dysfunction. Approximately 20% of cases of acute transverse myelitis occur in children. This review summarizes the current published literature on acute transverse myelitis, including epidemiology, diagnostic criteria, pathogenesis, clinical presentation, clinical evaluation, and differential diagnosis. The article also summarizes the neuroimaging features, acute and chronic complications, treatments, and prognosis of acute transverse myelitis in the pediatric population. The initial evaluation centers on differentiation from other causes of myelopathy, and cases are further divided into idiopathic or disease-associated acute transverse myelitis. Correct diagnosis is important for treatment and prognosis. Treatment begins with intensive surveillance for acute life-threatening respiratory or autonomic complications. Immunomodulating therapy is recommended for noninfectious causes, using high-dose intravenous corticosteroids or plasma exchange. Other therapeutic options are also discussed. Prognosis depends on a number of factors, and evidence suggests that the majority of children have a good outcome. A small percentage of children diagnosed with acute transverse myelitis later are diagnosed with other demyelinating diseases, especially neuromyelitis optica, or multiple sclerosis. The most common long-term complications of acute transverse myelitis are urinary, motor, or sensory dysfunction.

Idiopathic transverse myelitis and neuromyelitis optica: clinical profiles, pathophysiology and therapeutic choices

Transverse myelitis is a focal inflammatory disorder of the spinal cord which may arise due to different etiologies. Transverse myelitis may be idiopathic or related/secondary to other diseases including infections, connective tissue disorders and other autoimmune diseases. It may be also associated with optic neuritis (neuromyelitis optica), which may precede transverse myelitis. In this manuscript we review the pathophysiology of different types of transverse myelitis and neuromyelitis optica and discuss diagnostic criteria for idiopathic transverse myelitis and risk of development of multiple sclerosis after an episode of transverse myelitis. We also discuss treatment options including corticosteroids, immunosuppressives and monoclonal antibodies, plasma exchange and intravenous immunoglobulins.

Molecular mimicry as an inducing trigger for CNS autoimmune demyelinating disease

Summary:  Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) that affects about 0.1% of the worldwide population. This deleterious disease is marked by infiltration of myelin‐specific T cells that attack the protective myelin sheath that surrounds CNS nerve axons. Upon demyelination, saltatory nerve conduction is disrupted, and patients experience neurologic deficiencies. The exact cause for MS remains unknown, although most evidence supports the hypothesis that both genetic and environmental factors contribute to disease development. Epidemiologic evidence supports a role for environmental pathogens, such as viruses, as potentially key contributors to MS induction. Pathogens can induce autoimmunity via several well‐studied mechanisms with the most postulated being molecular mimicry. Molecular mimicry occurs when T cells specific for peptide epitopes derived from pathogens cross‐react with self‐epitopes, leading to autoimmune tissue destruction. In this review, we discuss an in vivo virus‐induced mouse model of MS developed in our laboratory, which has contributed greatly to our understanding of the mechanisms underlying molecular mimicry‐induced CNS autoimmunity.

The relevance of animal models in multiple sclerosis research

Multiple Sclerosis (MS) is a complex disease with an unknown etiology and no effective cure, despite decades of extensive research that led to the development of several partially effective treatments. Researchers have only limited access to early and immunologically active MS tissue samples, and the modification of experimental circumstances is much more restricted in human studies compared to studies in animal models. For these reasons, animal models are needed to clarify the underlying immune-pathological mechanisms and test novel therapeutic and reparative approaches. It is not possible for a single mouse model to capture and adequately incorporate all clinical, radiological, pathological and genetic features of MS. The three most commonly studied major categories of animal models of MS include: (1) the purely autoimmune experimental autoimmune/allergic encephalomyelitis (EAE); (2) the virally induced chronic demyelinating disease models, with the main model of Theiler's Murine Encephalomyelitis Virus (TMEV) infection and (3) toxin-induced models of demyelination, including the cuprizone model and focal demyelination induced by lyso-phosphatidyl choline (lyso-lecithine). EAE has been enormously helpful over the past several decades in our overall understanding of CNS inflammation, immune surveillance and immune-mediated tissue injury. Furthermore, EAE has directly led to the development of three approved medications for treatment in multiple sclerosis, glatiramer acetate, mitoxantrone and natalizumab. On the other hand, numerous therapeutical approaches that showed promising results in EAE turned out to be either ineffective or in some cases harmful in MS. The TMEV model features a chronic-progressive disease course that lasts for the entire lifespan in susceptible mice. Several features of MS, including the role and significance of axonal injury and repair, the partial independence of disability from demyelination, epitope spread from viral to myelin epitopes, the significance of remyelination has all been demonstrated in this model. TMEV based MS models also feature several MRI findings of the human disease. Toxin-induced demyelination models has been mainly used to study focal demyelination and remyelination. None of the three main animal models described in this review can be considered superior; rather, they are best viewed as complementary to one another. Despite their limitations, the rational utilization and application of these models to address specific research questions will remain one of the most useful tools in studies of human demyelinating diseases.

T cell receptor recognition of self and foreign antigens in the induction of autoimmunity

The major histocompatibility complex (MHC) on human chromosome 6 represents the most important genetic locus for a number of common human autoimmune diseases. Specific alleles that differ from closely related alleles by only one or a few amino acids in the peptide binding groove are frequently strongly associated with disease susceptibility, raising the important question of which peptide presentation events are critical in disease initiation and progression. This review will cover a number of topics pertinent to this fundamental question, including MHC linked disease susceptibility to autoimmune diseases, molecular mechanisms for the role of MHC molecules in autoimmune diseases as well as the recognition of self and microbial peptides by self-reactive T cell receptors (TCRs).

Theiler's murine encephalomyelitis virus as a vaccine candidate for immunotherapy

The induction of sterilizing T-cell responses to tumors is a major goal in the development of T-cell vaccines for treating cancer. Although specific components of anti-viral CD8+ immunity are well characterized, we still lack the ability to mimic viral CD8+ T-cell responses in therapeutic settings for treating cancers. Infection with the picornavirus Theiler's murine encephalomyelitis virus (TMEV) induces a strong sterilizing CD8+ T-cell response. In the absence of sterilizing immunity, the virus causes a persistent infection. We capitalized on the ability of TMEV to induce strong cellular immunity even under conditions of immune deficiency by modifying the virus to evaluate its potential as a T-cell vaccine. The introduction of defined CD8+ T-cell epitopes into the leader sequence of the TMEV genome generates an attenuated vaccine strain that can efficiently drive CD8+ T-cell responses to the targeted antigen. This virus activates T-cells in a manner that is capable of inducing targeted tissue damage and glucose dysregulation in an adoptive T-cell transfer model of diabetes mellitus. As a therapeutic vaccine for the treatment of established melanoma, epitope-modified TMEV can induce strong cytotoxic T-cell responses and promote infiltration of the T-cells into established tumors, ultimately leading to a delay in tumor growth and improved survival of vaccinated animals. We propose that epitope-modified TMEV is an excellent candidate for further development as a human T-cell vaccine for use in immunotherapy.

Interferon induced with helicase C domain 1 (IFIH1) and virus-induced autoimmunity: a review

In addition to genetic factors, environmental triggers, including viruses and other pathogens, are thought to play a major role in the development of autoimmune disease. Recent findings have shown that viral-induced autoimmunity is likely to be genetically determined. In large-scale genetic analyses, an association of interferon induced with helicase C domain 1 (IFIH1) gene variants encoding a viral RNA-sensing helicase with susceptibility to several autoimmune diseases was found. To date, the precise role of IFIH1 in pathogenic mechanisms of viral-induced autoimmunity has yet to be fully elucidated. However, recent reports suggest that IFIH1 may play a role in the etiology of type 1 diabetes. Rare IFIH1 alleles have been shown to be protective against diabetes, and their carriage correlates with lower production of this helicase and its functional disruption. In contrast, upregulation of IFIH1 expression by viruses is associated with more severe disease, and could exacerbate the autoimmune process in susceptible individuals.

Differential induction of experimental autoimmune encephalomyelitis by myelin basic protein molecular mimics in mice humanized for HLA-DR2 and an MBP(85-99)-specific T cell receptor

Multiple sclerosis (MS) is a chronic autoimmune neurological disease characterized by infiltration of peripheral inflammatory cells to the central nervous system (CNS) and demyelination of CNS white matter. Epidemiological evidence suggests a possible infectious trigger. One potential mechanism by which an infectious agent may trigger MS is via molecular mimicry wherein T cells generated against foreign epitopes cross-react with self-myelin epitopes, such as myelin basic protein (MBP), with sufficient sequence similarity. It has been previously reported that an MBP(85-99)-reactive T cell clone derived from an MS patient cross-reacted with multiple bacterial-derived mimic peptides in vitro. We show that the same mimic peptides can induce clinical disease in two different strains of mice transgenic for both a human MBP(85-99)-specific TCR and HLA-DR2 (MHC II), albeit with different disease patterns - relapsing-remitting vs. monophasic. Interestingly, clinical disease correlates with CNS infiltration of CD4(+) T cells and F4/80(+) macrophages, but not with in vitro proliferative or cytokine responses of splenocytes in response to either MBP(85-99) or its mimics.

Molecular mimics can induce novel self peptide-reactive CD4+ T cell clonotypes in autoimmune disease

It has been postulated that infectious agents may precipitate autoimmune disease when T cell responses raised against the pathogen cross-react with self-peptides, a phenomenon known as molecular mimicry. However, there are very little data available characterizing the similarity between the repertoire of the cross-reactive self-specific T cell population compared with the pathogen-specific T cell repertoire. In this study, we use immunoscope analysis to identify the T cell populations induced upon priming SJL/J mice with a pathogen-derived mimic of the immunodominant encephalitogenic myelin peptide PLP(139-151), which is contained within the protease IV protein of Haemophilus influenzae (HAE(574-586)). We describe an IFN-gamma-producing Vbeta19(+) T cell population in HAE(574-586)-primed mice that appears to be the "public clonotype" as it expanded in response to peptide in all mice tested. Critically this Vbeta19(+) T cell population is not expanded in mice primed with the self-peptide PLP(139-151), indicating that mimics can induce the expansion of new self-reactive populations not initially present in the periphery of a host. This is the first description of the use of immunoscope analysis to characterize the cross-reactive anti-self T cell response induced by a molecular mimic.

Sequential polymicrobial infections lead to CNS inflammatory disease: possible involvement of bystander activation in heterologous immunity

VV(PLP) is a recombinant vaccinia virus (VV) encoding myelin proteolipid protein (PLP) that has been used to investigate molecular mimicry and autoimmunity. Since virus infections can cause bystander activation, mice were first infected with VV(PLP), and later challenged with wild-type VV, lymphocytic choriomeningitis virus (LCMV), or murine cytomegalovirus (MCMV). Among the VV(PLP)-primed mice, only MCMV challenge induced significant Ki-67(+), CD3(+)T cell infiltration into the central nervous system (CNS) with a mild PLP antibody response. While MCMV alone caused no CNS disease, control VV-infected mice followed with MCMV developed mild CNS inflammation. Thus, heterologous virus infections can induce CNS pathology.

Structural requirements for initiation of cross-reactivity and CNS autoimmunity with a PLP139-151 mimic peptide derived from murine hepatitis virus

MS is an autoimmune CNS demyelinating disease in which infection appears to be an important pathogenic factor. Molecular mimicry, the cross‐activation of autoreactive T cells by mimic peptides from infectious agents, is a possible explanation for infection‐induced autoimmunity. Infection of mice with a non‐pathogenic strain of Theiler's murine encephalomyelitis virus (TMEV) engineered to express an epitope from Haemophilus influenzae (HI) sharing 6/13 amino acids with the dominant proteolipid protein (PLP) epitope, PLP_139–151, can induce CNS autoimmune disease. Here we demonstrate that another PLP_139–151 mimic sequence derived from murine hepatitis virus (MHV) which shares only 3/13 amino acids with PLP_139–151 can also induce CNS autoimmune disease, but only when delivered by genetically engineered TMEV, not by immunization with the MHV peptide. Further, we demonstrate the importance of proline at the secondary MHC class II contact residue for effective cross‐reactivity, as addition of this amino acid to the native MHV sequence increases its ability to cross‐activate PLP_139–151‐specific autoreactive T cells, while substitution of proline in the HI mimic peptide has the opposite effect. This study describes a structural requirement for potential PLP_139–151 mimic peptides, and provides further evidence for infection‐induced molecular mimicry in the pathogenesis of autoimmune disease.

Antigen presentation in autoimmunity and CNS inflammation: how T lymphocytes recognize the brain

The central nervous system (CNS) is traditionally viewed as an immune privileged site in which overzealous immune cells are prevented from doing irreparable damage. It was believed that immune responses occurring within the CNS could potentially do more damage than the initial pathogenic insult itself. However, virtually every aspect of CNS tissue damage, including degeneration, tumors, infection, and of course autoimmunity, involves a significant cellular inflammatory component. While the blood-brain barrier (BBB) inhibits diffusion of hydrophilic (immune) molecules across brain capillaries, activated lymphocytes readily pass the endothelial layer of postcapillary venules without difficulty. In classic neuro-immune diseases such as multiple sclerosis or acute disseminated encephalomyelitis, it is thought that neuroantigen-reactive lymphocytes, which have escaped immune tolerance, now invade the CNS and are responsible for tissue damage, demyelination, and axonal degeneration. The developed animal model for these disorders, experimental autoimmune encephalomyelitis (EAE), reflects many aspects of the human conditions. Studies in EAE proved that auto-reactive encephalitogenic T helper (Th) cells are responsible for the onset of the disease. Th cells recognize their cognate antigen (Ag) only when presented by professional Ag-presenting cells in the context of major histocompatibility complex class II molecules. The apparent target structures of EAE immunity are myelinating oligodendrocytes, which are not capable of presenting Ag to invading encephalitogenic T cells. A compulsory third party is thus required to mediate between the attacking T cells and the myelin-expressing target. This review will discuss the recent advances in this field of research and we will discuss the journey of an auto-reactive T cell from its site of activation into perivascular spaces and further into the target tissue.

Social stress alters the severity and onset of the chronic phase of Theiler's virus infection

Social stress alters the acute phase of Theiler's virus infection (TMEV), a model of multiple sclerosis. Stress applied prior to infection had deleterious disease outcomes, while stress applied concurrent with infection was protective. The current study examined multiple behavioral (motor impairment, open field activity) and immunological measures (IL-6, antibodies to virus and myelin proteins) in both the acute and chronic phases of TMEV. It was found that stress applied prior to infection exacerbated disease outcomes, while concurrent application was protective in both disease phases.

A virus-induced molecular mimicry model of multiple sclerosis

Multiple sclerosis1 (MS) is an immune-mediated autoimmune demyelinating disease in humans. The initiating event in MS is unknown, but epidemiological evidence suggests that virus infections may be important and one possible mechanism for induction of infection-induced autoimmune disease is molecular mimicry. To test the ability of a virus encoding a self myelin mimic epitope to induce an autoimmune response, we have developed a mouse model wherein the immunodominant myelin epitope PLP139-151, or mimics of this epitope, were inserted into a nonpathogenic variant of Theiler's murine encephalomyelitis virus (TMEV). SJL mice infected with TMEV containing PLP139-151 or a mimic of PLP139-151 expressed by the protease IV protein of Haemophilus influenzae, sharing only 6/13 amino acids with the native epitope, developed an early-onset demyelinating disease associated with activation of CD4+ T cells reactive with PLP139-151. We have used this molecular mimicry model to further address the requirements for mimic epitope processing and presentation during infection and the requirements for TCR recognition and MHC binding of mimic epitopes. We have also investigated whether molecular mimicry may require multiple infections, with either the mimic-encoding virus or an unrelated virus, to initiate autoimmune disease. Finally, we have asked whether a virus encoding a molecular mimic has to directly infect the target organ to induce autoimmune disease. Overall, this virus-induced molecular mimicry model has provided critical information regarding the mechanisms by which infection-induced molecular mimicry can induce autoimmune diseases.

The structural interactions between T cell receptors and MHC-peptide complexes place physical limits on self-nonself discrimination

The activation and expansion of T cells in an antimicrobial immune response is based on the ability of T cell receptors (TCR) to discriminate between MHC-bound peptides derived from different microbial agents as well as self-proteins. However, the specificity of T cells is constrained by the limited number of peptide side chains that are available for TCR binding. By considering the structural requirements for peptide binding to MHC molecules and TCR recognition of MHC-peptide complexes, we demonstrated that human T cell clones could recognize a number of peptides from different organisms that were remarkably distinct in their primary sequence. These peptides were particularly diverse at those sequence positions buried in pockets of the MHC binding site, whereas a higher degree of similarity was present at a limited number of peptide residues that created the interface with the TCR. These T cell clones had been isolated from multiple sclerosis patients with human myelin basic protein, demonstrating that activation of such autoreactive T cells by microbial peptides with sufficient structural similarity may contribute to the disease process. Similar findings have now been made for a variety of human and murine T cell clones, indicating that specificity and cross-reactivity are inherent properties of TCR recognition. The observations that particular TCR are highly sensitive to changes at particular peptide positions but insensitive to many other changes in peptide sequence are not contradictory, but rather the result of structural interactions in which a relatively flat TCR surface contacts a limited number of side chains from a peptide that is deeply embedded in the MHC binding site.

Innate (over)immunity and adaptive autoimmune disease

Autoimmune disease is characterized by clinical symptoms mediated by adaptive (T cell and B cell) immune reactions towards autoantigen-expressing tissue. Here we discuss that autoimmune disease is often preceded by autoreactivity, meaning the priming of autoantigen-specific immune cells without relevant tissue damage. Recent experimental evidence has demonstrated that both the induction of autoreactivity and the conversion into autoimmune disease is controlled by the activation of the nonspecific innate immune system. Also, the "inflammatory status" of the target organ critically influences the onset of overt autoimmune disease.

Gender bias in Theiler's virus-induced demyelinating disease correlates with the level of antiviral immune responses

Multiple sclerosis is an immune-mediated disease of the CNS and shows a sex-biased distribution in which 60-75% of all cases are female. A mouse model of multiple sclerosis, Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease, also displays a gender bias. However, in the C57L/J strain of mice, males are susceptible to disease whereas females are completely resistant. In this study we determined the gender differences in the TMEV-specific immune response, which may be responsible for the gender bias in clinical disease. Our data clearly demonstrate that female C57L/J mice induce significantly higher levels of TMEV-specific neutralizing Ab as well as a stronger peripheral T cell response throughout the course of viral infection. In contrast, male mice have a higher level of TMEV-specific CD4(+) and CD8(+) T cell infiltration into the CNS as well as viral persistence. These results suggest that a higher level of the initial antiviral immune response in female mice may be able to effectively clear virus from the periphery and CNS and therefore prevent further disease manifestations. Male mice in contrast do not mount as effective an immune response, thereby allowing for eventual viral persistence in the CNS and continuous T cell expansion leading to clinical symptoms.

Induction of antigen specific peripheral humoral tolerance to cardiac myosin does not prevent CB3-mediated autoimmune myocarditis

Chronic myocarditis often progresses to dilated cardiomyopathy resulting in heart failure or cardiac transplantation. Viral infection is the most common cause of myocarditis and coxsackie B viruses (CBV) are the most frequently cited etiologic agents associated with myocarditis and cardiomyopathy. Additionally, CBV infections of genetically susceptible mice induce autoimmune myocarditis resembling human disease, including the development of autoantibodies to cardiac myosin. Herein, we describe experiments in which peripheral tolerance to cardiac myosin was induced by administration of antigen-coupled antigen presenting cells. While the antibody response to cardiac myosin following CB3 infection was reduced, the viral induction of clinical autoimmune myocarditis was not affected. Additionally, viral replication was unaffected by the reduced humoral response to cardiac myosin. Therefore, the humoral response to cardiac myosin is not required for the development of autoimmunity following infection of NOD mice. This work demonstrates the difficulty in using antigen specific tolerance as a course of treatment to prevent multivalent autoimmune disorders.

Initiation and exacerbation of autoimmune demyelination of the central nervous system via virus-induced molecular mimicry: implications for the pathogenesis of multiple sclerosis

Epidemiological studies indicate that infectious agents are important in the pathogenesis of multiple sclerosis (MS). Our previous reports showed that the infection of SJL mice with a nonpathogenic variant of Theiler's murine encephalomyelitis virus (TMEV) engineered to express a naturally occurring Haemophilus influenzae-encoded molecular mimic (HI574-586) of an immunodominant self-myelin proteolipid protein epitope (PLP139-151) induced a rapid-onset demyelinating disease associated with the activation of PLP139-151-specific Th1 responses. The current results extend our previous findings in four critical respects. We show that disease initiation by the H. influenzae mimic is prevented by tolerance to the self PLP139-151 epitope, definitively proving the occurrence of infection-induced molecular mimicry. We demonstrate that the H. influenzae mimic epitope can be processed from the flanking sequences within the native mimic protein. We show that the H. influenzae mimic epitope only induces an immunopathologic self-reactive Th1 response and subsequent clinical disease in the context of the TMEV infection and not when administered in complete Freund's adjuvant, indicating that molecular mimicry-induced disease initiation requires virus-activated innate immune signals. Lastly, we show that the infection of SJL mice with TMEV expressing the H. influenzae mimic can exacerbate a previously established nonprogressive autoimmune disease of the central nervous system. Collectively, these findings illustrate the evolving mechanisms by which virus infections may contribute to both the initiation and exacerbation of autoimmune diseases, and they have important implications for MS pathogenesis.

How an autoimmune reaction triggered by molecular mimicry between streptococcal M protein and cardiac tissue proteins leads to heart lesions in rheumatic heart disease

Molecular mimicry between microbial antigens and host tissue is suggested as a mechanism for post-infectious autoimmune disease. In the present work we describe the autoimmune reactions of two severe rheumatic heart disease (RHD) patients, through an analysis of heart-infiltrating T-cell repertoire, antigen recognition, and cytokine production induced by specific antigens. T-cell clones derived from oligoclonally expanded T cells in the heart cross-recognized M5 peptides, heart tissue-derived proteins, and myosin peptides. We show, using binding affinity assays, that an immunodominant streptococcal peptide (M5(81-96)) is capable of binding to the HLA-DR53 molecule. The same peptide was recognized by an infiltrating T-cell clone from a patient carrying HLA-DR15, DR7, and DR53 molecules. This suggests that this peptide is probably presented to T cells in the context of the HLA-DR53 molecule. Cross-reactive heart-infiltrating T cells activated by the M5 protein and its peptides and by heart tissue-derived proteins produced predominantly inflammatory cytokines. Interleukin (IL)-4 was produced in small amounts by mitral valve intralesional T-cell lines and clones. Altogether, these results suggest that mimicry between streptococcal antigens and heart-tissue proteins, combined with high inflammatory cytokine and low IL-4 production, leads to the development of autoimmune reactions and cardiac tissue damage in RHD patients.

Viral Delivery of an Epitope fromHaemophilus influenzaeInduces Central Nervous System Autoimmune Disease by Molecular Mimicry

Multiple sclerosis (MS) is an autoimmune CNS demyelinating disease in which infection may be an important initiating factor. Pathogen-induced cross-activation of autoimmune T cells may occur by molecular mimicry. Infection with wild-type Theiler's murine encephalomyelitis virus induces a late-onset, progressive T cell-mediated demyelinating disease, similar to MS. To determine the potential of virus-induced autoimmunity by molecular mimicry, a nonpathogenic neurotropic Theiler's murine encephalomyelitis virus variant was engineered to encode a mimic peptide from protease IV of Haemophilus influenzae (HI), sharing 6 of 13 aa with the dominant encephalitogenic proteolipid protein (PLP) epitope PLP(139-151). Infection of SJL mice with the HI mimic-expressing virus induced a rapid-onset, nonprogressive paralytic disease characterized by potent activation of self-reactive PLP(139-151)-specific CD4(+) Th1 responses. In contrast, mice immunized with the HI mimic-peptide in CFA did not develop disease, associated with the failure to induce activation of PLP(139-151)-specific CD4(+) Th1 cells. However, preinfection with the mimic-expressing virus before mimic-peptide immunization led to severe disease. Therefore, infection with a mimic-expressing virus directly initiates organ-specific T cell-mediated autoimmunity, suggesting that pathogen-delivered innate immune signals may play a crucial role in triggering differentiation of pathogenic self-reactive responses. These results have important implications for explaining the pathogenesis of MS and other autoimmune diseases.

TCR affinity and negative regulation limit autoimmunity

Autoimmune diseases are often mediated by self-reactive T cells, which must be activated to cause immunopathology. One mechanism, known as molecular mimicry, proposes that self-reactive T cells may be activated by pathogens expressing crossreactive ligands. Here we have developed a model to investigate how the affinity of the T-cell receptor (TCR) for the activating agent influences autoimmunity. Our model shows that an approximately fivefold difference in the TCR affinity for the activating ligand results in a 50% reduction in the incidence of autoimmunity. A reduction in TCR-ligand affinity to approximately 20 times lower than normal does not induce autoimmunity despite the unexpected induction of cytotoxic T lymphocytes (CTLs) and insulitis. Furthermore, in the absence of a key negative regulatory molecule, Cbl-b, 100% of mice develop autoimmunity upon infection with viruses encoding the lower-affinity ligand. Therefore, autoimmune disease is sensitive both to the affinity of the activating ligand and to normal mechanisms that negatively regulate the immune response.

CD4 T-cell memory

CD4 T-cell memory is in some ways more enigmatic than CD8 T-cell memory. This is mostly due to the fact that CD4 T cells tend to expand far less in response to antigenic stimuli, thereby thwarting attempts at their detection during the course of an immune response. Nevertheless, there is a wide range of experimental models that have provided information regarding the survival and maintenance of CD4 memory cells, their functional capacities, their differentiation states and program of development following activation. The emerging picture is one of great versatility and functional heterogeneity as befits their central position within the immune system.

Novel insights in the regulation of the immune system: a report on the FASEB summer research conference on autoimmunity (June 14-19, 2003, Saxton's River, Vermont, USA)

The bi-annual FASEB autoimmunity conference organized last year by Betty Diamond and Stephen Miller brought together some 150 delegates studying various aspects of autoimmune diseases such as lupus, rheumatoid arthritis and autoimmune diabetes. The conference provided numerous insights into the latest research on autoimmunity and answered many basic research type questions that are important for understanding the complex nature of these diseases. Because some time has elapsed since the conference, data from a number of talks has already been published. Thus, I will present an overview of some of the most interesting and at the same time, still unpublished data on T cells presented at the conference. The balance between tolerance and immunity is controlled through a variety of mechanisms such as the presence or absence of co-stimulation or negative regulation of a T cell response. CD4+ CD25+ regulatory T cells were also a focus of interest. Talks that I will discuss focused on the role of molecules such as GITR, Foxp3 and B7 for the development and function of regulatory T cells and the importance of these molecules in the prevention of autoimmunity. As well, a novel form of CTLA-4 and the use of 4-1BB co-stimulation blockade for the control of autoimmunity will be discussed.

Gene therapy in autoimmune, demyelinating disease of the central nervous system

Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system (CNS), where suspected autoimmune attack causes nerve demyelination and progressive neurodegeneration and should benefit from both anti-inflammatory and neuroprotective strategies. Although neuroprotection strategies are relatively unexplored in MS, systemic delivery of anti-inflammatory agents to people with MS has so far been relatively disappointing. This is most probably because of the limited capacity of these molecules to enter the target tissue, because of exclusion by the blood-brain barrier. The complex natural history of MS also means that any therapeutic agents will have to be administered long-term. Gene therapy offers the possibility of site-directed, long-term expression, and is currently being preclinically investigated in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. While some immune effects may be targeted in the periphery using DNA vaccination, strategies both viral and nonviral are being developed to target agents into the CNS either via direct delivery or using the trafficking properties of cell-carrier systems. Targeting of leucocyte activation, cytokines and nerve growth factors have shown some promising benefit in animal EAE systems, the challenge will be their application in clinical use.

Hit-Hit and hit-Run: viruses in the playing field of multiple sclerosis

Viruses have been major players in the search for the cause of multiple sclerosis (MS). In support of the viral theory is the predominance of CD8+ T cells and class-I major histocompatibility complex in lesions, the powerful therapeutic effects of beta interferons, the ease of inducing demyelination in experimental models following virus challenge, and the documented examples of several human demyelinating diseases conclusively demonstrated to be of viral origin. We propose two hypotheses of how viruses may cause MS. In the "Hit-Hit" hypothesis, the virus persists or may be reactivated in the central nervous system (CNS). Injury is the result of direct viral damage and by an attempt of the immune response to clear the infectious agent. In the "Hit-Run" hypothesis, virus infects the periphery but never enters the CNS. The virus sets up an abnormal immunologic milieu for subsequent autoimmunity. In both scenarios, knowing the inciting virus would be expected to eliminate disease if the population were vaccinated to prevent infection. In the treatment of patients with fully established disease, the Hit-Hit hypothesis would require that antiviral agents enter the CNS and stop replication. In the case of the Hit-Run hypothesis, treatment of patients with established disease with antiviral agents would be futile.

Immunoregulation of a viral model of multiple sclerosis using the synthetic cannabinoid R+WIN55,212

Theiler murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) is a mouse model of chronic-progressive multiple sclerosis (MS) characterized by Th1-mediated CNS demyelination and spastic hindlimb paralysis. Existing MS therapies reduce relapse rates in 30% of relapsing-remitting MS patients, but are ineffective in chronic-progressive disease, and their effects on disability progression are unclear. Experimental studies demonstrate cannabinoids are useful for symptomatic treatment of spasticity and tremor in chronic-relapsing experimental autoimmune encephalomyelitis. Cannabinoids, however, have reported immunosuppressive properties. We show that the cannabinoid receptor agonist, R+WIN55,212, ameliorates progression of clinical disease symptoms in mice with preexisting TMEV-IDD. Amelioration of clinical disease is associated with downregulation of both virus and myelin epitope-specific Th1 effector functions (delayed-type hypersensitivity and IFN-gamma production) and the inhibition of CNS mRNA expression coding for the proinflammatory cytokines, TNF-alpha, IL1-beta, and IL-6. Clinical trials investigating the therapeutic potential of cannabinoids for the symptomatic treatment of MS are ongoing, and this study demonstrates that they may also have potent immunoregulatory properties.