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

Differential Microbial Pattern Description in Subjects with Autoimmune-Based Thyroid Diseases: A Pilot Study

The interaction between genetic susceptibility, epigenetic, endogenous, and environmental factors play a key role in the initiation and progression of autoimmune thyroid diseases (AITDs). Studies have shown that gut microbiota alterations take part in the development of autoimmune diseases. We have investigated the possible relationship between gut microbiota composition and the most frequent AITDs. A total of nine Hashimoto's thyroiditis (HT), nine Graves-Basedow's disease (GD), and 11 otherwise healthy donors (HDs) were evaluated. 16S rRNA pyrosequencing and bioinformatics analysis by Quantitative Insights into Microbial Ecology and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) were used to analyze the gut microbiota. Beta diversity analysis showed that gut microbiota from our groups was different. We observed an increase in bacterial richness in HT and a lower evenness in GD in comparison to the HDs. GD showed a significant increase of Fusobacteriaceae, Fusobacterium and Sutterella compared to HDs and the core microbiome features showed that Prevotellaceae and Prevotella characterized this group. Victivallaceae was increased in HT and was part of their core microbiome. Streptococcaceae, Streptococcus and Rikenellaceae were greater in HT compared to GD. Core microbiome features of HT were represented by Streptococcus, Alistipes, Anaerostipes, Dorea and Haemophilus. Faecalibacterium decreased in both AITDs compared to HDs. PICRUSt analysis demonstrated enrichment in the xenobiotics degradation, metabolism, and the metabolism of cofactors and vitamins in GD patients compared to HDs. Moreover, correlation studies showed that some bacteria were widely correlated with autoimmunity parameters. A prediction model evaluated a possible relationship between predominant concrete bacteria such as an unclassified genus of Ruminococcaceae, Sutterella and Faecalibacterium in AITDs. AITD patients present altered gut microbiota compared to HDs. These alterations could be related to the immune system development in AITD patients and the loss of tolerance to self-antigens.

Auto-reactivity against gut bacterial peptides in patients with late-onset diabetes

The depletion of gut mucosal barrier enables exposure of gut microbes/gut microbial products to the host mucosal immunity which may increase the risk of metabolic/inflammatory disorders. These immune responses can lead to the development of mild autoimmunity to metabolic peptides coming from gut bacteria and may result in metabolic diseases like late-onset diabetes (LOD). In the present study, we identified host sera cross-reactivity with gut bacterial peptides similar to host proteins. The interaction between diabetic sera and gut peptides was detected by enzyme-linked immunosorbent assay (ELISA) and results were confirmed using surface plasmon resonance (SPR). The ELISA assay showed a higher level of serum cross-reactivity in LOD patients as compared to non-diabetic controls against three peptides (P-5, P-9, and P-13). SPR analysis confirmed binding-affinity against P-5 and P-13. Also, a significant correlation was observed between inflammatory markers and P-5. This study demonstrates that gut health is important not only for intestinal diseases but also for several late-onset diseases, like, diabetes.

Autoimmune pathogenesis of Chagas heart disease: looking back, looking ahead

Chagas heart disease is an inflammatory cardiomyopathy that develops in approximately one-third of individuals infected with the protozoan parasite Trypanosoma cruzi. Since the discovery of T. cruzi by Carlos Chagas >100 years ago, much has been learned about Chagas disease pathogenesis; however, the outcome of T. cruzi infection is highly variable and difficult to predict. Many mechanisms have been proposed to promote tissue inflammation, but the determinants and the relative importance of each have yet to be fully elucidated. The notion that some factor other than the parasite significantly contributes to the development of myocarditis was hypothesized by the first physician-scientists who noted the conspicuous absence of parasites in the hearts of those who succumbed to Chagas disease. One of these factors-autoimmunity-has been extensively studied for more than half a century. Although questions regarding the functional role of autoimmunity in the pathogenesis of Chagas disease remain unanswered, the development of autoimmune responses during infection clearly occurs in some individuals, and the implications that this autoimmunity may be pathogenic are significant. In this review, we summarize what is known about the pathogenesis of Chagas heart disease and conclude with a view of the future of Chagas disease diagnosis, pathogenesis, therapy, and prevention, emphasizing recent advances in these areas that aid in the management of Chagas disease.

Killer-cell immunoglobulin-like receptor expression on lymphocyte subsets in multiple sclerosis patients treated with interferon-β: evaluation as biomarkers for clinical response

BACKGROUND

Both the adaptative and the innate immune systems interplay in multiple sclerosis (MS) pathogeny. Killer-cell immunoglobulin-like receptors (KIRs) are key regulators of the immune response, with activating and inhibitory isoforms.

OBJECTIVE

In this study we analysed whether the expression of KIR isoforms is implicated in MS pathogenesis and in the therapeutic response to interferon (IFN)-β.

METHODS

Peripheral blood samples were collected from 78 IFN-β-treated MS patients and 46 healthy controls (HC). KIR expression was evaluated by flow cytometry on natural killer (NK) and T cells.

RESULTS

The expression of KIRs on NK cells and T lymphocytes did not differ between MS patients and HC. IFN-β therapy decreased the expression of KIR2DL1/2DS1 and increased that of KIR2DL2/3 on NK cells. This therapy also reduced KIR2DL1/2DS1, KIR2DL2/2DL3 and KIR3DL2 expression on CD8(+) T cells. The baseline evaluation of the percentage of circulating CD16(+) NK cells was predictive of the clinical response to IFN-β; however, response to this therapy did not appear related to KIR expression.

CONCLUSIONS

This study shows that expression of KIR isoforms on NK and T lymphocytes correlated in different ways with IFN-β therapy, suggesting that KIR dynamics may be associated with the pathways involved in the mechanisms of action of IFN-β.

Demyelination in multiple sclerosis

This review, focused on demyelination in multiple sclerosis, is divided in two parts. The first part addresses the many and not exclusive mechanisms leading to demyelination in the central nervous system. Although the hypothesis that a primary oligodendrocyte or myelin injury induces a secondary immune response in the central nervous system is still a matter of debate, most recent advances underline the influence of a primary immune response against myelin antigen(s), with a diversity of potential targets. Whereas multiple sclerosis was long considered as a T cell-mediated disease, the role of B lymphocytes is now increasingly recognized, and the influence of antibodies on tissue damage actively investigated. The second part of the review describes the axonal consequences of demyelination. Segmental demyelination results in conduction block or slowing of conduction through adaptative responses, notably related to modifications in the distribution of voltage gated sodium channels along the denuded axon. If demyelination persists, these changes, as well as the loss of trophic and metabolic support, will lead to irreversible axonal damage and loss. In this respect, favouring early myelin repair, during a window of time when axonal damage is still reversible, might pave the way for neuroprotection.

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.

Epitope spreading of the anti-CYP2D6 antibody response in patients with autoimmune hepatitis and in the CYP2D6 mouse model

Autoimmune hepatitis (AIH) is a serious chronic inflammatory disease of the liver with yet unknown etiology and largely uncertain immunopathology. The hallmark of type 2 AIH is the generation of liver kidney microsomal-1 (LKM-1) autoantibodies, which predominantly react to cytochrome P450 2D6 (CYP2D6). The identification of disease initiating factors has been hampered in the past, since antibody epitope mapping was mostly performed using serum samples collected late during disease resulting in the identification of immunodominant epitopes not necessarily representing those involved in disease initiation. In order to identify possible environmental triggers for AIH, we analyzed for the first time the spreading of the anti-CYP2D6 antibody response over a prolonged period of time in AIH patients and in the CYP2D6 mouse model, in which mice infected with Adenovirus-human CYP2D6 (Ad-h2D6) develop antibodies with a similar specificity than AIH patients. Epitope spreading was analyzed in six AIH-2-patients and in the CYP2D6 mouse model using SPOTs membranes containing peptides covering the entire CYP2D6 protein. Despite of a considerable variation, both mice and AIH patients largely focus their humoral immune response on an immunodominant epitope early after infection (mice) or diagnosis (patients). The CYP2D6 mouse model revealed that epitope spreading is initiated at the immunodominant epitope and later expands to neighboring and remote regions. Sequence homologies to human pathogens have been detected for all identified epitopes. Our study demonstrates that epitope spreading does indeed occur during the pathogenesis of AIH and supports the concept of molecular mimicry as a possible initiating mechanism for AIH.

Molecular mimicry in multiple sclerosis

Two main etiological components are considered important in human autoimmune diseases including multiple sclerosis (MS), first the immunogenetic background and second environmental factors. Among the latter, infectious organisms are probably the most relevant, and epidemiological studies in MS firmly support that viral infections often precede disease exacerbations or the onset of MS. Infectious agents can contribute to disease development or phenotypic expression in different ways. Our focus will be directed on molecular mimicry, i.e. antigenic similarity between structural epitopes or peptide sequences from infectious organisms with those found in self proteins of the host. The intriguing concept of molecular mimicry has evolved substantially since its introduction over 20 years ago. We will summarize the most important developments and discuss puzzling questions, which remain open despite many claims that molecular mimicry is involved in the development of human autoimmune disease after infections or vaccinations.

Murine monoclonal antibody 26 raised against tetanus toxoid cross-reacts with beta2-glycoprotein I: its characteristics and role in molecular mimicry

PROBLEM

Studies on experimental antiphospholipid syndrome (APS) models proved that molecular mimicry between plasma protein beta(2)-glycoprotein I (beta(2)GPI) and structure within micro-organisms or their products, might be a cause for experimental APS. Considering the heterogeneity of polyclonal antiphospholipid antibodies (aPLs), it is important to define the precise characteristics of pathogenic aPLs. To avoid the influence of polyclonality and to further analyse the connection between molecular mimicry and APS, we produced monoclonal antibodies (MAbs) against tetanus toxoid (TTd) and tested their reactivity against beta(2)GPI.

METHOD OF STUDY

In this report, we analysed the characteristics of MAb26 raised against TTd and cross-reactive with beta(2)GPI: its binding properties in various in vitro immunoassays, its specific interactions with surface epitopes expressed on apoptotic cells and its role in vivo.

RESULTS

We have demonstrated that MAb26: (i) binds beta(2)GPI being immobilized on an appropriate surface: irradiated polystyrene plates, non-irradiated plates pre-coated with anionic phospholipids and polyvinylidene fluoride membrane; (ii) binds specifically to apoptotic but not to viable cells and the binding is beta(2)GPI-dependent; and (iii) induces a pathologic pregnancy outcome when passively injected into BALB/c mice.

CONCLUSION

This study concluded that certain subpopulations of antibodies raised against TTd and cross-reactive with beta(2)GPI, because of the molecular mimicry mechanism, could have pathologic potential.

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 mimicry between neurons and an intracerebral pathogen induces a CD8 T cell-mediated autoimmune disease

To identify basic mechanisms of how infections may induce a neuron-specific autoimmune response, we generated mice expressing OVA as neuronal autoantigen under control of the neuron-specific enolase promoter (NSE-OVA mice). Intracerebral, but not systemic, infection with attenuated Listeria monocytogenes-secreting OVA induced an atactic-paretic neurological syndrome in NSE-OVA mice after bacterial clearance from the brain, whereas wild-type mice remained healthy. Immunization with attenuated Listeria monocytogenes-secreting OVA before intracerebral infection strongly increased the number of intracerebral OVA-specific CD8 T cells aggravating neurological disease. T cell depletion and adoptive transfer experiments identified CD8 T cells as decisive mediators of the autoimmune disease. Importantly, NSE-OVA mice having received OVA-specific TCR transgenic CD8 T cells developed an accelerated, more severe, and extended neurological disease. Adoptively transferred pathogenic CD8 T cells specifically homed to OVA-expressing MHC class I(+) neurons and, corresponding to the clinical symptoms, approximately 30% of neurons in the anterior horn of the spinal cord became apoptotic. Thus, molecular mimicry between a pathogen and neurons can induce a CD8 T cell-mediated neurological disease, with its severity being influenced by the frequency of specific CD8 T cells, and its induction, but not its symptomatic phase, requiring the intracerebral presence of the pathogen.

Multiple sclerosis and regulatory T cells

INTRODUCTION

Multiple sclerosis (MS) is a complex genetic disease characterized by chronic inflammation of the central nervous system (CNS). The pathology of MS is largely attributed to autoreactive effector T cells that penetrate the blood-brain barrier and become activated within the CNS. As autoreactive T cells are present in the blood of both patients with MS and healthy individuals, other regulatory mechanisms exist to prevent autoreactive T cells from causing immune disorders. Active suppression by regulatory T (Treg) cells plays a key role in the control of self-antigen-reactive T cells and the induction of peripheral tolerance in vivo. In particular, the importance of antigen-specific Treg cells in conferring genetic resistance to organ-specific autoimmunity and in limiting autoimmune tissue damage has been documented in many disease models including MS.

RESULTS

We have found that the frequency of Tregs in MS patients is unchanged from controls, but their function measured in vitro may be diminished, correlating with impaired inhibitory activity in vivo. This review discusses the immunopathology of MS with particular focus given to regulatory T cells and their potential for the development of new therapies to treat this disease.

Avidity maturation of memory CD8 T cells is limited by self-antigen expression

Immune tolerance to self-antigens is a complex process that utilizes multiple mechanisms working in concert to maintain homeostasis and prevent autoimmunity. We developed a system that revealed a population of self-specific CD8 T cells within the endogenous T cell repertoire. Immunization of ovalbumin (OVA)-expressing transgenic mice with recombinant viruses expressing OVA-peptide variants induced self-reactive T cells in vivo that matured into memory T cells able to respond to secondary infection. However, whereas the avidity of memory cells in normal mice increased dramatically with repeated immunizations, avidity maturation was limited for self-specific CD8 T cells. Despite decreased avidity, such memory cells afforded protection against infection, but did not induce overt autoimmunity. Further, up-regulation of self-antigen expression in dendritic cells using an inducible system promoted programmed death-1 expression, but not clonal expansion of preexisting memory cells. Thus, the self-reactive T cell repertoire is controlled by overlapping mechanisms influenced by antigen dose.

Breaking tolerance to the natural human liver autoantigen cytochrome P450 2D6 by virus infection

Autoimmune liver diseases, such as autoimmune hepatitis (AIH) and primary biliary cirrhosis, often have severe consequences for the patient. Because of a lack of appropriate animal models, not much is known about their potential viral etiology. Infection by liver-tropic viruses is one possibility for the breakdown of self-tolerance. Therefore, we infected mice with adenovirus Ad5 expressing human cytochrome P450 2D6 (Ad-2D6). Ad-2D6–infected mice developed persistent autoimmune liver disease, apparent by cellular infiltration, hepatic fibrosis, “fused” liver lobules, and necrosis. Similar to type 2 AIH patients, Ad-2D6–infected mice generated type 1 liver kidney microsomal–like antibodies recognizing the immunodominant epitope WDPAQPPRD of cytochrome P450 2D6 (CYP2D6). Interestingly, Ad-2D6–infected wild-type FVB/N mice displayed exacerbated liver damage when compared with transgenic mice expressing the identical human CYP2D6 protein in the liver, indicating the presence of a stronger immunological tolerance in CYP2D6 mice. We demonstrate for the first time that infection with a virus expressing a natural human autoantigen breaks tolerance, resulting in a chronic form of severe, autoimmune liver damage. Our novel model system should be instrumental for studying mechanisms involved in the initiation, propagation, and precipitation of virus-induced autoimmune liver diseases.

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.

Molecular mimicry and auto-immunity

The term "molecular mimicry" was coined by R. Damian in 1964, who was first to suggest that antigenic determinants of micro-organisms may resemble antigenic determinants of their host. Damian suggested that this similarity served as a defense mechanism of a microorganism from the host's immune system and prevented the development of immune response to the micro-organism, thereby protecting it from host defense. Years later, the term "molecular mimicry" was attributed a different meaning-namely, antigenic determinants of microorganisms might elicit an auto-immune response that harms the host. The concept of molecular mimicry is based on a structural similarity between a pathogen or metabolite and self-structures. The similarity could be expressed as shared amino acid sequences (linear or mimotope) or similar conformational structure between a pathogen and self-antigen. "Molecular mimicry" has become a very popular explanation for the frequent association of infection with auto-immune disease.

Pathogenic epitopes, heterologous immunity and vaccine design

Vaccine strategies are focused on developing protective responses to immunogenic peptide epitopes of pathogens that are normally recognized by T and B cells. However, some epitopes stimulate crossreactive T-cell responses between pathogens and can prime a host to damaging pathology on infection with the crossreactive pathogen. The removal of potentially pathogenic epitopes from vaccines might enhance prophylaxis and reduce the risk of side effects of vaccine-associated disease.

Substantial research has been directed towards the development of a new generation of vaccines that are based on the inclusion of immunogenic epitopes in recombinant vectors. Here we examine the evidence that under certain conditions immunogenic epitopes can do more harm than good and might therefore be considered pathogenic. We suggest that the specific removal of such pathogenic epitopes from vaccines might increase their prophylactic potential, while minimizing the risk of side-effects from vaccine use.

Cross-reactivity between peptide mimics of the immunodominant myelin proteolipid protein epitope PLP139-151: comparison of peptide priming in CFA vs. viral delivery

Epidemiological evidence suggests that pathogens may trigger the development of autoimmune diseases such as multiple sclerosis (MS). Pathogens may trigger disease via molecular mimicry, wherein T cells generated against foreign epitopes are also cross-reactive with self-epitopes. Five pathogen-derived molecular mimics of PLP(139-151) (the immunodominant CD4(+) T cell myelin epitope in SJL mice) were previously identified. This study examines the degree of cross-reactivity between the different mimics, comparing mice primed with mimic peptide in CFA with mice infected with recombinant mimic-expressing viruses. The pattern of in vitro reactivity and ability to induce CNS disease differs between peptide priming and virus infection.

Molecular mimicry in multiple sclerosis

One of the most common demyelinating central nervous system (CNS) diseases in humans is multiple sclerosis (MS). The disease can be very debilitating with vision loss, motor and sensory disturbances, and cognitive impairment. The clinical course may present as a relapsing-remitting disease course, a progressive disease course, or a combination thereof. The etiology of MS is unknown. Though many viruses have been shown to be associated with MS, no one virus has ever been demonstrated to be the cause of MS. In addition, MS is thought to have an autoimmune component. Molecular mimicry is one hypothesis put forth which could reconcile the diverse pathology and etiology of MS. Molecular mimicry occurs when peptides from pathogens share sequence or structural similarities with self-antigens. Infection with various pathogens, each with its individual molecular mimic to a CNS antigen, may explain the inability of investigators to link one specific virus to MS. Molecular mimicry may be mediated through human leukocyte antigen class I- and class II-restricted T cells and antibodies, which may explain the diversity in phenotype. Aspects of molecular mimicry will be discussed in relation to each of these immune system components. Examples of various molecular mimics will be discussed with a particular focus on the CNS and MS. Molecular mimicry alone may not be able to induce disease; priming of the immune system by infection with a pathogen that carries a molecular mimic to self may have to be followed by a later nonspecific immunologic challenge in order for disease to be initiated. Recent research into this priming and triggering of disease will be discussed in relation to an animal model for MS.

The human CMV-UL86 peptide 981–1003 shares a crossreactive T-cell epitope with the encephalitogenic MOG peptide 34–56, but lacks the capacity to induce EAE in rhesus monkeys

Rhesus monkeys immunized with MOG(34-56), a dominant T-cell epitope from myelin/oligodendrocyte glycoprotein, develop an acute neurological disease resembling acute disseminated encephalomyelitis (ADEM) in humans. The typical large demyelinated lesions and mononuclear infiltrates in the monkey brains are caused by MOG(34-56) T-cells. We show that MOG(34-56)-reactive CD4+ and CD8+ T-cells are induced in monkeys immunized with a peptide from the human CMV major capsid protein (UL86; 981-1003), that shares sequence similarity with MOG(34-56). Monkeys sensitized against the viral peptide and subsequently challenged with MOG(34-56) display histological signs of encephalitis, but do not show overt neurological signs.

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.

When T cells recognize a pattern, they might cause trouble

The mechanisms of self and non-self discrimination by T cells remain a fascinating topic for immunologists. How the immune system achieves protection of the host against an ever-changing realm of pathogens using a rather limited repertoire of T-cell receptors and at the same time avoids inflicting damage against its own tissues is equally puzzling. Although a better understanding of these questions has come from studies of the extent of cross reactivity of T-cell clones specific for foreign or self antigens, and also from examination of the different antigen avidities by which they recognize either type of antigen, many details are still lacking. Recently, there has been investigation into how T cells of the adaptive immune system can recognize functional protein domains or amino acid patterns. This type of T-cell reactivity is reminiscent of the pattern recognition that is firmly established as an important function of innate immune receptors such as Toll-like receptors. Many functional protein domains are conserved in evolution and are shared by a wide spectrum of pathogens, as well as by proteins of animals and humans. Hence, pattern recognition by adaptive immune cells might represent an efficient mechanism for host protection by the above-mentioned limited number of T-cell receptors. However, the fact that such functional domains occur so frequently in nature also implies that pattern recognition by T cells might cause autoimmunity, and recent data support this hypothesis.

Proteomic definition of a desmoglein linear determinant common to Pemphigus vulgaris and Pemphigus foliaceous

Background

A number of autoimmune diseases have been clinically and pathologically characterized. In contrast, target antigens have been identified only in a few cases and, in these few cases, the knowledge of the exact epitopic antigenic sequence is still lacking. Thus the major objective of current work in the autoimmunity field is the identification of the epitopic sequences that are related to autoimmune reactions. Our labs propose that autoantigen peptide epitopes able to evoke humoral (auto)immune response are defined by the sequence similarity to the host proteome. The underlying scientific rationale is that antigen peptides acquire immunoreactivity in the context of their proteomic similarity level. Sequences uniquely owned by a protein will have high potential to evoke an immune reaction, whereas motifs with high proteomic redundancy should be immunogenically silenced by the tolerance phenomenon. The relationship between sequence redundancy and peptide immunoreactivity has been successfully validated in a number of experimental models. Here the hypothesis has been applied to pemphigus diseases and the corresponding desmoglein autoantigens.

Methods

Desmoglein 3 sequence similarity analysis to the human proteome followed by dot-blot/NMR immunoassays were carried out to identify and validate possible epitopic sequences.

Results

Computational analysis led to identifying a linear immunodominant desmoglein-3 epitope highly reactive with the sera from Pemphigus vulgaris as well as Pemphigus foliaceous. The epitopic peptide corresponded to the amino acid REWVKFAKPCRE sequence, was located in the extreme N-terminal region (residues 49 to 60), and had low redundancy to the human proteome. Sequence alignment showed that human desmoglein 1 and 3 share the REW-KFAK–RE sequence as a common motif with 75% residue identity.

Conclusion

This study 1) validates sequence redundancy to autoproteome as a main factor in shaping desmoglein peptide immunogenicity; 2) offers a molecular mechanicistic basis in analyzing the commonality of autoimmune responses exhibited by the two forms of pemphigus; 3) indicates possible peptide-immunotherapeutical approaches for pemphigus diseases.

Reshaping the past: Strategies for modulating T-cell memory immune responses

Memory T cells are generated following an initial encounter with antigen, persist over the lifetime of an individual, and mediate rapid and robust functional responses upon antigenic recall. While immune memory is generally associated with protective immune response to pathogens, memory T cells can be generated to diverse types of antigens including autoantigens and alloantigens through homologous or crossreactive priming and comprise the majority of circulating T cells during adulthood. Memory T cells can therefore play critical roles in propagating and perpetuating autoimmune disease and in mediating allograft rejection, although the precise pathways for regulation of memory immune responses remain largely undefined. Moreover, evaluating and designing strategies to modulate memory T-cell responses are challenging given the remarkable heterogeneity of memory T cells, with different subsets predominating in lymphoid versus non-lymphoid tissue sites. In this review, we discuss what is presently known regarding the effect of current immunomodulation strategies on the memory T-cell compartment and potential strategies for controlling immunological recall.

Mechanisms of immunopathology in murine models of central nervous system demyelinating disease

Many disorders of the CNS, such as multiple sclerosis (MS), are characterized by the loss of the myelin sheath surrounding nerve axons. MS is associated with infiltration of inflammatory cells into the brain and spinal cord, which may be the primary cause of demyelination or which may be induced secondary to axonal damage. Both the innate and adaptive arms of the immune system have been reported to play important roles in myelin destruction. Numerous murine demyelinating models, both virus-induced and/or autoimmune, are available, which reflect the clinical and pathological variability seen in human disease. This review will discuss the immunopathologic mechanisms involved in these demyelinating disease models.

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.

T cell mimicry and epitope specificity of cross-reactive T cell clones from rheumatic heart disease

Mimicry between streptococcal M protein and cardiac myosin is important in the pathogenesis of rheumatic heart disease. M protein-specific human T cell clones derived from rheumatic carditis were cross-reactive with human cardiac myosin, and laminin, a valve protein. Among the 11 CD4(+) and CD8(+) cross-reactive T cell clones, at least 6 different reactivity patterns were distinguished, suggesting different degrees of cross-reactivity and a very diverse T cell repertoire. The latter was confirmed by a heterogeneous Vbeta gene and CDR3 usage. HLA restriction and Th1 cytokine production in response to rM6 protein were preserved when the T cell clones were stimulated by human cardiac myosin or other alpha-helical proteins, such as tropomyosin and laminin. The cross-reactive human T cell clones proliferated to B2 and B3A, dominant peptide epitopes in the B repeat region of streptococcal M protein. In human cardiac myosin, epitopes were demonstrated in the S2 and light meromyosin regions. In our study, T cell mimicry was defined as recognition of structurally related Ags involved in disease and recognized by the same T cell. Mimicry in our study was related to alpha-helical coiled coil proteins which have a repetitive seven-aa residue periodicity that maintains alpha-helical structure and thus creates a high number of degenerate possibilities for recognition by T cells. The study of human T cell clones from rheumatic heart disease revealed potential sites of T cell mimicry between streptococcal M protein and human cardiac myosin and represents some of the most well-defined T cell mimicry in human autoimmune disease.

Infections and autoimmunity--good or bad?

The relationship between infections and autoimmunity is complex. Current evidence indicates that microbes can initiate, enhance, or, conversely, abrogate autoimmunity. In this paper, we will review experimental examples illustrating mechanisms involved in these three scenarios. Microbial infections can act as environmental triggers inducing or promoting autoimmunity resulting in clinical manifestations of autoimmune disease in genetically predisposed individuals. However, increasing evidence suggests the opposite outcome, which is the prevention or amelioration of autoimmune processes following microbial encounters. These latter observations support conceptually the "hygiene hypothesis," suggesting that cleaner living conditions will lead to enhanced incidence of autoimmune disorders, asthma, and allergies. Because proof of concept in humans is difficult to obtain, we will discuss relevant animal model data in context with likely or proven human associations. Knowledge of mechanisms that underlie either positive or negative effects of infections on autoimmunity will facilitate exploration of molecular details for prospective clinical studies in the future.

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.