Recognition of conserved amino acid motifs of common viruses and its role in autoimmunity

Nocardia farcinica brain abscess with torque teno virus co-infection: A case report

Background

Brain abscesses caused by Nocardia are rare and difficult to diagnose. Nocardia farcinica is among the most common species; however, the conventional diagnosis of N. farcinica infection consists of cerebrospinal fluid (CSF) and blood culture and Gram staining. These procedures prolong the time to diagnosis and initiating treatment.

Case presentation

A 69-year-old woman with diabetes mellitus presented with headaches and dizziness persisting for 2 weeks, which was initially diagnosed as a brain abscess. Due to the unusual presentation and rapid progression of symptoms, she underwent surgical resection of the brain abscess. No pathogens were detected in blood or CSF cultures. However, metagenomic next-generation sequencing (mNGS) identified N. farcinica and Torque teno virus in pus extracted from the abscesses. The patient received appropriate antibiotic therapy and recovered fully without any residual neurological deficits.

Conclusion

mNGS useful for prompt diagnosis and selection of antibiotic therapy for brain abscesses caused by Nocardia. Surgical intervention is necessary in some cases.

The mysterious anelloviruses: investigating its role in human diseases

Anelloviruses (AVs) that infect the human population are members of the Anelloviridae family. They are widely distributed in human populations worldwide. Torque teno virus (TTV) was the first virus of this family to be identified and is estimated to be found in the serum of 80-90% of the human population. Sometime after the identification of TTV, Torque teno mini virus (TTMV) and Torque teno midi virus (TTMDV) were also identified and classified in this family. Since identifying these viruses, have been detected in various types of biological fluids of the human body, including blood and urine, as well as vital organs such as the liver and kidney. They can be transmitted from person to person through blood transfusions, fecal-oral contact, and possibly sexual intercourse. Recent studies on these newly introduced viruses show that although they are not directly related to human disease, they may be indirectly involved in initiating or exacerbating some human population-related diseases and viral infections. Among these diseases, we can mention various types of cancers, immune system diseases, viral infections, hepatitis, and AIDS. Also, they likely use the microRNAs (miRNAs) they encode to fulfill this cooperative role. Also, in recent years, the role of proliferation and their viral load, especially TTV, has been highlighted to indicate the immune system status of immunocompromised people or people who undergo organ transplants. Here, we review the possible role of these viruses in diseases that target humans and highlight them as important viruses that require further study. This review can provide new insights to researchers.

Anelloviruses versus human immunity: how do we control these viruses?

One continuous companion and one of the major players in the human blood virome are members of the Anelloviridae family. Anelloviruses are probably found in all humans, infection occurs early in life and the composition (anellome) is thought to remain stable and personal during adulthood. The stable anellome implies a great balance between the host immune system and the virus. However, the lack of a robust culturing system hampers direct investigation of interactions between virus and host cells. Other techniques, however, including next generation sequencing, AnelloScan-antibody tests, evolution selection pressure analysis, and virus protein structures, do provide new insights into the interactions between anelloviruses and the host immune system. This review aims at providing an overview of the current knowledge on the immune mechanisms acting on anelloviruses and the countering viral mechanisms allowing immune evasion.

Microbial peptides activate tumour-infiltrating lymphocytes in glioblastoma

Microbial organisms have key roles in numerous physiological processes in the human body and have recently been shown to modify the response to immune checkpoint inhibitors1,2. Here we aim to address the role of microbial organisms and their potential role in immune reactivity against glioblastoma. We demonstrate that HLA molecules of both glioblastoma tissues and tumour cell lines present bacteria-specific peptides. This finding prompted us to examine whether tumour-infiltrating lymphocytes (TILs) recognize tumour-derived bacterial peptides. Bacterial peptides eluted from HLA class II molecules are recognized by TILs, albeit very weakly. Using an unbiased antigen discovery approach to probe the specificity of a TIL CD4+ T cell clone, we show that it recognizes a broad spectrum of peptides from pathogenic bacteria, commensal gut microbiota and also glioblastoma-related tumour antigens. These peptides were also strongly stimulatory for bulk TILs and peripheral blood memory cells, which then respond to tumour-derived target peptides. Our data hint at how bacterial pathogens and bacterial gut microbiota can be involved in specific immune recognition of tumour antigens. The unbiased identification of microbial target antigens for TILs holds promise for future personalized tumour vaccination approaches.

Epstein-Barr virus and multiple sclerosis: moving from questions of association to questions of mechanism

The link between Epstein-Barr virus (EBV) and multiple sclerosis (MS) has puzzled researchers since it was first discovered over 40 years ago. Until that point, EBV was primarily viewed as a cancer-causing agent, but the culmination of evidence now shows that EBV has a pivotal role in development of MS. Early MS disease is characterised by episodic neuroinflammation and focal lesions in the central nervous system (CNS) that over time develop into progressive neurodegeneration and disability. Risk of MS is vanishingly low in EBV seronegative individuals, history of infectious mononucleosis (acute symptomatic primary infection with EBV) significantly increases risk and elevated antibody titres directed against EBV antigens are well-characterised in patients. However, the underlying mechanism - or mechanisms - responsible for this interplay remains to be fully elucidated; how does EBV-induced immune dysregulation either trigger or drive MS in susceptible individuals? Furthermore, deep understanding of virological and immunological events during primary infection and long-term persistence in B cells will help to answer the many questions that remain regarding MS pathogenesis. This review discusses the current evidence and mechanisms surrounding EBV and MS, which have important implications for the future of MS therapies and prevention.

Revisiting IgG Antibody Reactivity to Epstein-Barr Virus in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Its Potential Application to Disease Diagnosis

Infections by the Epstein-Barr virus (EBV) are often at the disease onset of patients suffering from Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). However, serological analyses of these infections remain inconclusive when comparing patients with healthy controls (HCs). In particular, it is unclear if certain EBV-derived antigens eliciting antibody responses have a biomarker potential for disease diagnosis. With this purpose, we re-analyzed a previously published microarray data on the IgG antibody responses against 3,054 EBV-related antigens in 92 patients with ME/CFS and 50 HCs. This re-analysis consisted of constructing different regression models for binary outcomes with the ability to classify patients and HCs. In these models, we tested for a possible interaction of different antibodies with age and gender. When analyzing the whole data set, there were no antibody responses that could distinguish patients from healthy controls. A similar finding was obtained when comparing patients with non-infectious or unknown disease trigger with healthy controls. However, when data analysis was restricted to the comparison between HCs and patients with a putative infection at their disease onset, we could identify stronger antibody responses against two candidate antigens (EBNA4_0529 and EBNA6_0070). Using antibody responses to these two antigens together with age and gender, the final classification model had an estimated sensitivity and specificity of 0.833 and 0.720, respectively. This reliable case-control discrimination suggested the use of the antibody levels related to these candidate viral epitopes as biomarkers for disease diagnosis in this subgroup of patients. To confirm this finding, a follow-up study will be conducted in a separate cohort of patients.

Identification of B Cell and T Cell Epitopes Using Synthetic Peptide Combinatorial Libraries

This article presents a combinatorial library method that consists of the synthesis and screening of mixture-based synthetic combinatorial libraries of peptide molecules to identify B and T cell epitopes. The protocols employ peptide libraries to identify peptides recognized by MAbs and T cells. The first protocol uses a positional scanning peptide library made up of hexapeptides to identify antigenic determinants recognized by MAbs. The 120 mixtures in the hexapeptide library are tested for their inhibitory activity in a competitive ELISA. The second protocol uses a decapeptide library to identify T cell peptide ligands. The 200 mixtures of the decapeptide library are tested for their ability to induce T cell activation. Support protocols cover optimization of the assay conditions for each MAb or T cell, to achieve the best level of sensitivity and reproducibility, and preparation of a hexapeptide library, along with deconvolution approaches. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Screening peptide library for antibody inhibition Basic Protocol 2: Screening a peptide library to identify CD4⁺ Or CD8⁺ T cell ligands Support Protocol 1: Optimizing antigen and antibody concentrations for screening assay Support Protocol 2: Preparing a positional scanning peptide library.

Delivery Mode Shapes the Composition of the Lower Airways Microbiota in Newborns

Radical alterations in the human microbiota composition are well-known to be associated with many pathological conditions. If these aberrations are established at the time of birth, the risk of developing correlated pathologies throughout life is significantly increased. For this reason, all newborns should begin their lives with a proper microbiota in each body district. The present study aimed at demonstrating a correlation between the mode of delivery and the development of a well-balanced microbiota in the lower airways of newborns. 44 pregnant women were enrolled in this study. Microbiological comparative analysis was carried out on tracheobronchial secretions of babies born through vaginal delivery (VD) or caesarean section (CS). All samples showed the presence of bacterial DNA, regardless of the mode of delivery. No viable cultivable bacteria were isolated from the CS samples. On the contrary, VD allowed colonization of the lower airways by alive cultivable bacteria. The identification of bacterial species revealed that Lactobacillus spp. and Bacteroides vulgatus were the most common microorganisms in the lower airways of vaginally-delivered newborns. Data obtained from quantitative PCRs showed a significantly higher total bacterial load, as well as Firmicutes and Lactobacillus spp. amount, in VD samples than CS ones, while no statistically significant difference was found in Torque Teno Virus (TTV) load between samples. Taken together, our findings confirm the hypothesis that passage through the maternal vaginal canal determines more beneficial colonization of the lower airways in newborns.

Multiple sclerosis: doubling down on MHC

Human leukocyte antigen (HLA)-encoded surface molecules present antigenic peptides to T lymphocytes and play a key role in adaptive immune responses. Besides their physiological role of defending the host against infectious pathogens, specific alleles serve as genetic risk factors for autoimmune diseases. For multiple sclerosis (MS), an autoimmune disease that affects the brain and spinal cord, an association with the HLA-DR15 haplotype was described in the early 1970s. This short opinion piece discusses the difficulties of disentangling the details of this association and recent observations about the functional involvement of not only one, but also the second gene of the HLA-DR15 haplotype. This information is not only important for understanding the pathomechanism of MS, but also for antigen-specific therapies.

Beryllium-specific CD4+ T cells induced by chemokine neoantigens perpetuate inflammation

Discovering dominant epitopes for T cells, particularly CD4+ T cells, in human immune-mediated diseases remains a significant challenge. Here, we used bronchoalveolar lavage (BAL) cells from HLA-DP2-expressing patients with chronic beryllium disease (CBD), a debilitating granulomatous lung disorder characterized by accumulations of beryllium-specific (Be-specific) CD4+ T cells in the lung. We discovered lung-resident CD4+ T cells that expressed a disease-specific public CDR3β T cell receptor motif and were specific to Be-modified self-peptides derived from C-C motif ligand 4 (CCL4) and CCL3. HLA-DP2-CCL/Be tetramer staining confirmed that these chemokine-derived peptides represented major antigenic targets in CBD. Furthermore, Be induced CCL3 and CCL4 secretion in the lungs of mice and humans. In a murine model of CBD, the addition of LPS to Be oxide exposure enhanced CCL4 and CCL3 secretion in the lung and significantly increased the number and percentage of CD4+ T cells specific for the HLA-DP2-CCL/Be epitope. Thus, we demonstrate a direct link between Be-induced innate production of chemokines and the development of a robust adaptive immune response to those same chemokines presented as Be-modified self-peptides, creating a cycle of innate and adaptive immune activation.

Cerebrospinal Fluid Analysis for Viruses by Metagenomic Next-Generation Sequencing in Pediatric Encephalitis: Not Yet Ready for Prime Time?

BACKGROUND

Metagenomic next-generation sequencing offers an unbiased approach to identifying viral pathogens in cerebrospinal fluid of patients with meningoencephalitis of unknown etiology.

METHODS

In an 11-month case series, we investigated the use of cerebrospinal fluid metagenomic next-generation sequencing to diagnose viral infections among pediatric hospitalized patients presenting with encephalitis or meningoencephalitis of unknown etiology. Cerebrospinal fluid from patients with known enterovirus meningitis were included as positive controls. Cerebrospinal fluid from patients with primary intracranial hypertension were included to serve as controls without known infections.

RESULTS

Cerebrospinal fluid metagenomic next-generation sequencing was performed for 37 patients. Among 27 patients with encephalitis or meningoencephalitis, 4 were later diagnosed with viral encephalitis, 6 had non-central nervous system infections with central nervous system manifestations, 6 had no positive diagnostic tests, and 11 were found to have a noninfectious diagnosis. Metagenomic next-generation sequencing identified West Nile virus (WNV) in the cerebrospinal fluid of 1 immunocompromised patient. Among the 4 patients with known enterovirus meningitis, metagenomic next-generation sequencing correctly identified enteroviruses and characterized the viral genotype. No viral sequences were detected in the cerebrospinal fluid of patients with primary intracranial hypertension. Metagenomic next-generation sequencing also identified sequences of nonpathogenic torque Teno virus in cerebrospinal fluid specimens from 13 patients.

CONCLUSIONS

Our results showed viral detection by cerebrospinal fluid metagenomic next-generation sequencing only in 1 immunocompromised patient and did not offer a diagnostic advantage over conventional testing. Viral phylogenetic characterization by metagenomic next-generation sequencing could be used in epidemiologic investigations of some viral pathogens, such as enteroviruses. The finding of torque Teno viruses in cerebrospinal fluid by metagenomic next-generation sequencing is of unknown significance but may merit further exploration for a possible association with noninfectious central nervous system disorders.

Viral Infections and Systemic Lupus Erythematosus: New Players in an Old Story

A causal link between viral infections and autoimmunity has been studied for a long time and the role of some viruses in the induction or exacerbation of systemic lupus erythematosus (SLE) in genetically predisposed patients has been proved. The strength of the association between different viral agents and SLE is variable. Epstein-Barr virus (EBV), parvovirus B19 (B19V), and human endogenous retroviruses (HERVs) are involved in SLE pathogenesis, whereas other viruses such as Cytomegalovirus (CMV) probably play a less prominent role. However, the mechanisms of viral-host interactions and the impact of viruses on disease course have yet to be elucidated. In addition to classical mechanisms of viral-triggered autoimmunity, such as molecular mimicry and epitope spreading, there has been a growing appreciation of the role of direct activation of innate response by viral nucleic acids and epigenetic modulation of interferon-related immune response. The latter is especially important for HERVs, which may represent the molecular link between environmental triggers and critical immune genes. Virus-specific proteins modulating interaction with the host immune system have been characterized especially for Epstein-Barr virus and explain immune evasion, persistent infection and self-reactive B-cell "immortalization". Knowledge has also been expanding on key viral proteins of B19-V and CMV and their possible association with specific phenotypes such as antiphospholipid syndrome. This progress may pave the way to new therapeutic perspectives, including the use of known or new antiviral drugs, postviral immune response modulation and innate immunity inhibition. We herein describe the state-of-the-art knowledge on the role of viral infections in SLE, with a focus on their mechanisms of action and potential therapeutic targets.

Viruses belonging to Anelloviridae or Circoviridae as a possible cause of chronic fatigue

Chronic fatigue often starts with an acute viral infection-as witnessed in the case of SARS-CoV-2-but indirect consequences of these infections are presumably the actual cause of the condition. As recently reviewed in this journal, the culprit could be a virus already present in the patient. The review covers several types of viruses, but concludes that the question is still open. The focus is on well known, pathogenic viruses for which there are ample diagnostic tools. I argue that there is one lesser-known group of viruses, the related anello- and circoviruses, which ought to be investigated. More or less everyone harbours at least one strain of these viruses in the blood, while not in the spinal fluid. They normally replicate at a low level, but their activity increases in an immune suppressed host; and there are cases where they do reach the brain. The initial infection could facilitate their access to the brain.

Torque teno virus microRNA detection in cerebrospinal fluids of patients with neurological pathologies

BACKGROUND

Torque teno virus (TTV) is a widespread anellovirus that establishes persistent infections in humans and represents the most abundant component of the human virome. TTV encodes microRNAs (miRNA) which are found both in viremic and not viremic subjects being potentially ideal tools for the virus to evade the immune system response and to maintain chronic infection in the host.

OBJECTIVE

To investigate TTV-DNA loads and TTV-miRNAs expression in cerebrospinal fluids (CSF) from subjects under analysis for the assessment of neurological diseases.

STUDY DESIGN

Detection of TTV-DNA and TTV-miRNAs (e. g. miRNA t1a, t3b, and tth8) were carried out from CSF samples of 93 subjects with neurological diseases by using universal real-time PCR, real-time RT-PCR, and next-generation sequencing (NGS) analyses.

RESULTS

TTV-DNA was detected in 11 of 93 (12 %) CSFs with a mean TTV load of 155 copies/mL. Conversely, 29 CSF samples (31 %) were positive for at least one TTV-miRNA, while 15 (16 %) CSFs contained all the TTV-miRNAs examined. Overall, TTV-miRNA tth8 was detected in 62 % of samples, followed by TTV miRNA t3b (56 %), and t1a (29 %). Interestingly, TTV-miRNAs were found in CSF samples that were negative for the presence of TTV-DNA. Next-generation sequencing analysis carried out from 4 TTV-DNA negative CSF samples detected reads mapped in TTV-miRNA sequences region.

CONCLUSIONS

These results shed novel light on the relationship between TTV and the central nervous system and make compelling furthered studies for investigating the potential role of TTV-miRNAs in neurological disorders.

Torque teno viruses in health and disease

Torque teno viruses (TTVs) are small, ubiquitous, viruses with a highly diverse, single-stranded, negative sense DNA genome and wide host range. They are detected at high rates in both healthy and diseased individuals and are considered a significant part of the mammalian virome. Similar to human TTVs, swine TTVs (TTSuVs) are epidemiologically linked to several coinfections including porcine circovirus types 2 and 3 and the porcine reproductive and respiratory disease syndrome virus. Experimental infection of gnotobiotic pigs with TTSuVs resulted in lesions in multiple organs and exacerbation of coinfections, making TTSuVs the only members of the Anelloviridae family with experimental evidence for pathogenicity. However, due to the lack of reliable cell culture and animal models, mechanistic studies on viral immunity and pathogenesis are limited. The objective of this review is to summarize the current status of knowledge regarding the biology, detection, pathogenesis and public health significance of TTSuVs, while identifying gaps in knowledge which limit the field.

Heterologous immune responses in health and disease

Immunological memory and tolerance represent major achievements and advantages of adaptive immunity. Organisms bearing adaptive immunity display prominent competitive advantages in the fight against infections. Memory immune cells are preserved for decades and are able to repel a second attack of an infectious agent. However, studies performed in the XXI century have shown that even unrelated pathogens may be quickly and effectively destroyed by memory cells. This type of response is called heterologous so that heterologous immune response is mainly typical to viral infections and other intracellular infections, where T-cells play a lead role in protection. This review will discuss various mechanisms involved in implementing T-cell cross-reactivity, describe molecular prerequisites for heterologous T-cell responses. Experimental evidence of memory T-cell potential to heterologous immune response in mouse models and in human infections are also discussed. Heterologous immune response is an important immune arm in adults and the elderly when the yield of naive cells to the periphery declines due to thymus involution. Along with obvious advantages, heterologous immune response leads to imbalanced memory T-cell repertoire, replacement of immunodominant epitopes with minor ones allowing viruses to evade immune response that results in virus persistence, or, conversely, fulminant infection course. Another threat of heterologous immune response due to switch in dominant repertoire of recognizable epitopes is presented by random self-epitope recognition, which can lead to development of autoimmune pathology. Heterologous immunity can also disrupt drug-induced tolerance in organ and tissue transplants and lead to graft rejection. Heterologous immune response should be taken into consideration while developing and using new vaccines, especially in adults and the elderly.

GDP-l-fucose synthase is a CD4+ T cell-specific autoantigen in DRB3*02:02 patients with multiple sclerosis

Multiple sclerosis is an immune-mediated autoimmune disease of the central nervous system that develops in genetically susceptible individuals and likely requires environmental triggers. The autoantigens and molecular mimics triggering the autoimmune response in multiple sclerosis remain incompletely understood. By using a brain-infiltrating CD4⁺ T cell clone that is clonally expanded in multiple sclerosis brain lesions and a systematic approach for the identification of its target antigens, positional scanning peptide libraries in combination with biometrical analysis, we have identified guanosine diphosphate (GDP)-l-fucose synthase as an autoantigen that is recognized by cerebrospinal fluid-infiltrating CD4⁺ T cells from HLA-DRB3*-positive patients. Significant associations were found between reactivity to GDP-l-fucose synthase peptides and DRB3*02:02 expression, along with reactivity against an immunodominant myelin basic protein peptide. These results, coupled with the cross-recognition of homologous peptides from gut microbiota, suggest a possible role of this antigen as an inducer or driver of pathogenic autoimmune responses in multiple sclerosis.

Viremia preceding multiple sclerosis: Two nested case-control studies

Infections have been suggested to be involved in Multiple Sclerosis (MS). We used metagenomic sequencing to detect both known and yet unknown microorganisms in 2 nested case control studies of MS. Two different cohorts were followed for MS using registry linkages. Serum samples taken before diagnosis as well as samples from matched control subjects were selected. In cohort1 with 75 cases and 75 controls, most viral reads were Anelloviridae-related and >95% detected among the cases. Among samples taken up to 2 years before MS diagnosis, Anellovirus species TTMV1, TTMV6 and TTV27 were significantly more common among cases. In cohort2, 93 cases and 93 controls were tested under the pre-specified hypothesis that the same association would be found. Although most viral reads were again related to Anelloviridae, no significant case-control differences were seen. We conclude that the Anelloviridae-MS association may be due to multiple hypothesis testing, but other explanations are possible.

Two new species of betatorqueviruses identified in a human melanoma that metastasized to the brain

The role of viral infections in the etiology of brain cancer remains uncertain. Prior studies mostly focused on transcriptome or viral DNA integrated in tumor cells. To investigate for the presence of viral particles, we performed metagenomics sequencing on viral capsid-protected nucleic acids from 12 primary and 8 metastatic human brain tumors. One brain tumor metastasized from a skin melanoma harbored two new human anellovirus species, Torque teno mini virus Emory1 (TTMV Emory1) and Emory2 (TTMV Emory2), while the remaining 19 samples did not reveal any exogenous viral sequences. Their genomes share 63-67% identity with other TTMVs, and phylogenetic clustering supports their classification within the Betatorquevirus genus. This is the first identification of betatorqueviruses in brain tumors. The viral DNA was in its expected non-integrated circular form, and it is unclear if the viruses contributed to tumor formation. Whether the viruses originated from blood, or the primary skin tumor could not be ascertained. Overall, our results demonstrate the usefulness of viral metagenomics to detect previously unknown exogenous virus in human brain tumors. They further suggest that active viral infections are rare events in brain tumors, but support a follow-up larger scale study to quantify their frequency in different brain tumor subtypes.

Viruses with Circular Single-Stranded DNA Genomes Are Everywhere!

Circular single-stranded DNA viruses infect archaea, bacteria, and eukaryotic organisms. The relatively recent emergence of single-stranded DNA viruses, such as chicken anemia virus (CAV) and porcine circovirus 2 (PCV2), as serious pathogens of eukaryotes is due more to growing awareness than to the appearance of new pathogens or alteration of existing pathogens. In the case of the ubiquitous human circular single-stranded DNA virus family Anelloviridae, there is still no convincing direct causal relation to any specific disease. However, infections may play a role in autoimmunity by changing the homeostatic balance of proinflammatory cytokines and the human immune system, indirectly affecting the severity of diseases caused by other pathogens. Infections with CAV (family Anelloviridae, genus Gyrovirus) and PCV2 (family Circoviridae, genus Circovirus) are presented here because they are immunosuppressive and affect health in domesticated animals. CAV shares genomic organization, genomic orientation, and common features of major proteins with human anelloviruses, and PCV2 DNA may be present in human food and vaccines.

Identification of heterologous Torque Teno Viruses in humans and swine

Torque Teno Viruses (TTVs) are ubiquitous viruses which are highly prevalent in several mammalian species. Human TTV’s are epidemiologically associated with several human disease conditions such as respiratory illnesses, auto-immune disorders and hepatitis. Recently it was found that swine TTV’s (TTSuVs) can act as primary pathogens. The common occurrence of TTVs as environmental contaminants and the increasing interest in the use of swine organs for xenotransplantation lend importance to the question of whether TTV’s can cross-infect across species. In this study, we examined human and swine sera by swine or human TTV-specific PCRs, to determine whether swine TTVs (TTSuV) DNA can be detected in humans and vice versa. Surprisingly, both human and TTSuV DNA were present in a majority of the samples tested. Transfection of human PBMC’s with TTSuV1 genomic DNA resulted in productive viral infection which was sustained for the three serial passages tested. Lymphoproliferative responses in infected human PBMCs were diminished when compared to the controls. Furthermore, mild to moderate antibody responses against the TTSuV1 ORF2 protein was detected in 16 of the 40 human sera by ELISA. Therefore, these study findings provide initial and fundamental evidence for possible cross-species transmission of TTVs.

In situ expansion of T cells that recognize distinct self-antigens sustains autoimmunity in the CNS

Polyspecific T cells recognizing multiple distinct self-antigens have been identified in multiple sclerosis and other organ-specific autoimmune diseases, but their pathophysiological relevance remains undetermined. Using a mouse model of multiple sclerosis, we show that autoimmune encephalomyelitis induction is strictly dependent on reactivation of pathogenic T cells by a peptide (35-55) derived from myelin oligodendrocyte glycoprotein (MOG). This disease-inducing response wanes after onset. Strikingly, the progression of disease is driven by the in situ activation and expansion of a minority of MOG35-55-specific T cells that also recognize neurofilament-medium (NF-M)15-35, an intermediate filament protein expressed in neurons. This mobilization of bispecific T cells is critical for disease progression as adoptive transfer of NF-M15-35/MOG35-55 bispecific T cell lines caused full-blown disease in wild-type but not NF-M-deficient recipients. Moreover, specific tolerance through injection of NF-M15-35 peptide at the peak of disease halted experimental autoimmune encephalomyelitis progression. Our findings highlight the importance of polyspecific autoreactive T cells in the aggravation and perpetuation of central nervous system autoimmunity.

Central role of Th2/Tc2 lymphocytes in pattern II multiple sclerosis lesions

OBJECTIVE

Multiple sclerosis (MS) is a disease of the central nervous system with marked heterogeneity in several aspects including pathological processes. Based on infiltrating immune cells, deposition of humoral factors and loss of oligodendrocytes and/or myelin proteins, four lesion patterns have been described. Pattern II is characterized by antibody and complement deposition in addition to T-cell infiltration. MS is considered a T-cell-mediated disease, but until now the study of pathogenic T cells has encountered major challenges, most importantly the limited access of brain-infiltrating T cells. Our objective was to identify, isolate, and characterize brain-infiltrating clonally expanded T cells in pattern II MS lesions.

METHODS

We used next-generation sequencing to identify clonally expanded T cells in demyelinating pattern II brain autopsy lesions, subsequently isolated these as T-cell clones from autologous cerebrospinal fluid and functionally characterized them.

RESULTS

We identified clonally expanded CD8(+) but also CD4(+) T cells in demyelinating pattern II lesions and for the first time were able to isolate these as live T-cell clones. The functional characterization shows that T cells releasing Th2 cytokines and able to provide B cell help dominate the T-cell infiltrate in pattern II brain lesions.

INTERPRETATION

Our data provide the first functional evidence for a putative role of Th2/Tc2 cells in pattern II MS supporting the existence of this pathogenic phenotype and questioning the protective role that is generally ascribed to Th2 cells. Our observations are important to consider for future treatments of pattern II MS patients.

B Cells and Autoantibodies in Multiple Sclerosis

While over the past decades T cells have been considered key players in the pathogenesis of multiple sclerosis (MS), it has only recently become evident that B cells have a major contributing role. Our understanding of the role of B cells has evolved substantially following the clinical success of B cell-targeting therapies and increasing experimental evidence for significant B cell involvement. Rather than mere antibody-producing cells, it is becoming clear that they are team players with the capacity to prime and regulate T cells, and function both as pro- and anti-inflammatory mediators. However, despite tremendous efforts, the target antigen(s) of B cells in MS have yet to be identified. The first part of this review summarizes the clinical evidence and results from animal studies pointing to the relevance of B cells in the pathogenesis of MS. The second part gives an overview of the currently known potential autoantigen targets. The third part recapitulates and critically appraises the currently available B cell-directed therapies.

Exploring the origins of grey matter damage in multiple sclerosis

Multiple sclerosis is characterized at the gross pathological level by the presence of widespread focal demyelinating lesions of the myelin-rich white matter. However, it is becoming clear that grey matter is not spared, even during the earliest phases of the disease. Furthermore, grey matter damage may have an important role both in physical and cognitive disability. Grey matter pathology involves both inflammatory and neurodegenerative mechanisms, but the relationship between the two is unclear. Histological, immunological and neuroimaging studies have provided new insight in this rapidly expanding field, and form the basis of the most recent hypotheses on the pathogenesis of grey matter damage.

Human anelloviruses: an update of molecular, epidemiological and clinical aspects

Human torque teno viruses (TTVs) are new, emerging infectious agents, recently assigned to the family Anelloviridae. The first representative of the genus, torque teno virus (TTV), was discovered in 1997, followed by torque teno mini virus (TTMV) in 2000, and torque teno midi virus (TTMDV) in 2007. These viruses are characterized by an extremely high prevalence, with relatively uniform distribution worldwide and a high level of genomic heterogeneity, as well as an apparent pan-tropism at the host level. Although these viruses have a very high prevalence in the general population across the globe, neither their interaction with their hosts nor their direct involvement in the etiology of specific diseases are fully understood. Since their discovery, human anelloviruses, and especially TTV, have been suggested to be associated with various diseases, such as hepatitis, respiratory diseases, cancer, hematological and autoimmune disorders, with few arguments for their direct involvement. Recent studies have started to reveal interactions between TTVs and the host's immune system, leading to new hypotheses for potential pathological mechanisms of these viruses. In this review article, we discuss the most important aspects and current status of human TTVs in order to guide future studies.

Bispecificity for myelin and neuronal self-antigens is a common feature of CD4 T cells in C57BL/6 mice

The recognition of multiple ligands by a single TCR is an intrinsic feature of T cell biology, with important consequences for physiological and pathological processes. Polyspecific T cells targeting distinct self-antigens have been identified in healthy individuals as well as in the context of autoimmunity. We have previously shown that the 2D2 TCR recognizes the myelin oligodendrocyte glycoprotein epitope (MOG)35-55 as well as an epitope within the axonal protein neurofilament medium (NF-M15-35) in H-2(b) mice. In this study, we assess whether this cross-reactivity is a common feature of the MOG35-55-specific T cell response. To this end, we analyzed the CD4 T cell response of MOG35-55-immunized C57BL/6 mice for cross-reactivity with NF-M15-35. Using Ag recall responses, we established that an important proportion of MOG35-55-specific CD4 T cells also responded to NF-M15-35 in all mice tested. To study the clonality of this response, we analyzed 22 MOG35-55-specific T cell hybridomas expressing distinct TCR. Seven hybridomas were found to cross-react with NF-M15-35. Using an alanine scan of NF-M18-30 and an in silico predictive model, we dissected the molecular basis of cross-reactivity between MOG35-55 and NF-M15-35. We established that NF-M F24, R26, and V27 proved important TCR contacts. Strikingly, the identified TCR contacts are conserved within MOG38-50. Our data indicate that due to linear sequence homology, part of the MOG35-55-specific T cell repertoire of all C57BL/6 mice also recognizes NF-M15-35, with potential implications for CNS autoimmunity.

Expression of dual-specificity phosphatase 5 pseudogene 1 (DUSP5P1) in tumor cells

Sequencing of individual clones from a newly established cDNA library from the chemoresistant Hodgkin's lymphoma cell line L-1236 led to the isolation of a cDNA clone corresponding to a short sequence from chromosome 1. Reverse transcriptase-polymerase chain reaction indicated high expression of this sequence in Hodgkin's lymphoma derived cell lines but not in normal blood cells. Further characterization of this sequence and the surrounding genomic DNA revealed that this sequence is part of a human endogenous retrovirus locus. The sequence of this endogenous retrovirus is interrupted by a pseudogene of the dual specificity phosphatase 5 (DUSP5). Reverse transcriptase-polymerase chain reaction revealed high expression of this pseudogene (DUSP5P1) in HL cell lines but not in normal blood cells or Epstein-Barr virus-immortalized B cells. Cells from other tumor types (Burkitt's lymphoma, leukemia, neuroblastoma, Ewing sarcoma) also showed a higher DUSP5P1/DUSP5 ratio than normal cells. Furthermore, we observed that higher expression of DUSP5 in relation to DUSP5P1 correlated with the expression of the pro-apoptotic factor B cell leukemia/lymphoma 2-like 11 (BCL2L11) in peripheral blood cells and HL cells. Knock-down of DUSP5 in HL cells resulted in down-regulation of BCL2L11. Thus, the DUSP5/DUSP5P1 system could be responsible for regulation of BCL2L11 leading to inhibition of apoptosis in these tumor cells.

A molecular view of multiple sclerosis and experimental autoimmune encephalitis: what can we learn from the epitope data?

An analysis to inventory all immune epitope data related to multiple sclerosis (MS) was performed using the Immune Epitope Database (IEDB). The analysis revealed that MS related data represent >20% of all autoimmune data, and that studies of EAE predominate; only 22% of the references describe human data. To date, >5800 unique peptides, analogs, mimotopes, and/or non-protein epitopes have been reported from 861 references, including data describing myelin-containing, as well as non-myelin antigens. This work provides a reference point for the scientific community of the universe of available data for MS-related adaptive immunity in the context of EAE and human disease.

Tracing environmental markers of autoimmunity: introducing the infectome

We recently introduced the concept of the infectome as a means of studying all infectious factors which contribute to the development of autoimmune disease. It forms the infectious part of the exposome, which collates all environmental factors contributing to the development of disease and studies the sum total of burden which leads to the loss of adaptive mechanisms in the body. These studies complement genome-wide association studies, which establish the genetic predisposition to disease. The infectome is a component which spans the whole life and may begin at the earliest stages right up to the time when the first symptoms manifest, and may thus contribute to the understanding of the pathogenesis of autoimmunity at the prodromal/asymptomatic stages. We provide practical examples and research tools as to how we can investigate disease-specific infectomes, using laboratory approaches employed from projects studying the “immunome” and “microbiome”. It is envisioned that an understanding of the infectome and the environmental factors that affect it will allow for earlier patient-specific intervention by clinicians, through the possible treatment of infectious agents as well as other compounding factors, and hence slowing or preventing disease development.

HLA-DR15-derived self-peptides are involved in increased autologous T cell proliferation in multiple sclerosis

The HLA-DR15 haplotype confers the largest part of the genetic risk to develop multiple sclerosis, a prototypic CD4+ T cell-mediated autoimmune disease. The mechanisms how certain HLA-class II molecules functionally contribute to autoimmune diseases are still poorly understood, but probably involve shaping an autoimmune-prone T cell repertoire during central tolerance in the thymus and subsequently maintaining or even expanding it in the peripheral immune system. Self-peptides that are presented by disease-associated HLA-class II molecules most likely play important roles during both processes. Here, we examined the functional involvement of the HLA-DR15 haplotype in autologous proliferation in multiple sclerosis and the contribution of HLA-DR15 haplotype-derived self-peptides in an in vitro system. We observe increased autologous T cell proliferation in patients with multiple sclerosis in relation to the multiple sclerosis risk-associated HLA-DR15 haplotype. Assuming that the spectrum of self-peptides that is presented by the two HLA-DR15 allelic products is important for sustaining autologous proliferation we performed peptide elution and identification experiments from the multiple sclerosis-associated DR15 molecules and a systematic analysis of a DR15 haplotype-derived self-peptide library. We identify HLA-derived self-peptides as potential mediators of altered autologous proliferation. Our data provide novel insights about perturbed T cell repertoire dynamics and the functional involvement of the major genetic risk factor, the HLA-DR15 haplotype, in multiple sclerosis.

Infectome: a platform to trace infectious triggers of autoimmunity

The "exposome" is a term recently used to describe all environmental factors, both exogenous and endogenous, which we are exposed to in a lifetime. It represents an important tool in the study of autoimmunity, complementing classical immunological research tools and cutting-edge genome wide association studies (GWAS). Recently, environmental wide association studies (EWAS) investigated the effect of environment in the development of diseases. Environmental triggers are largely subdivided into infectious and non-infectious agents. In this review, we introduce the concept of the "infectome", which is the part of the exposome referring to the collection of an individual's exposures to infectious agents. The infectome directly relates to geoepidemiological, serological and molecular evidence of the co-occurrence of several infectious agents associated with autoimmune diseases that may provide hints for the triggering factors responsible for the pathogenesis of autoimmunity. We discuss the implications that the investigation of the infectome may have for the understanding of microbial/host interactions in autoimmune diseases with long, pre-clinical phases. It may also contribute to the concept of the human body as a superorganism where the microbiome is part of the whole organism, as can be seen with mitochondria which existed as microbes prior to becoming organelles in eukaryotic cells of multicellular organisms over time. A similar argument can now be made in regard to normal intestinal flora, living in symbiosis within the host. We also provide practical examples as to how we can characterise and measure the totality of a disease-specific infectome, based on the experimental approaches employed from the "immunome" and "microbiome" projects.

Identification of B cell and T cell epitopes using synthetic peptide combinatorial libraries

This unit presents a combinatorial library method that consists of the synthesis and screening of mixture-based synthetic combinatorial libraries of peptide molecules. The protocols employ peptide libraries to identify peptides recognized by MAbs and T cells. The first protocol uses a positional scanning peptide library made up of hexapeptides to identify antigenic determinants recognized by MAbs. The 120 mixtures in the hexapeptide library are tested for their inhibitory activity in a competitive ELISA. The second protocol uses a decapeptide library to identify T cell peptide ligands. The 200 mixtures of the decapeptide library are tested for their ability to induce T cell activation. Support protocols cover optimization of the assay conditions for each MAb or T cell, to achieve the best level of sensitivity and reproducibility, and preparation of a hexapeptide library, along with deconvolution approaches.

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

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

T lymphocyte priming by neutrophil extracellular traps links innate and adaptive immune responses

Polymorphonuclear neutrophils constitute the first line of defense against infections. Among their strategies to eliminate pathogens they release neutrophil extracellular traps (NETs), being chromatin fibers decorated with antimicrobial proteins. NETs trap and kill pathogens very efficiently, thereby minimizing tissue damage. Furthermore, NETs modulate inflammatory responses by activating plasmacytoid dendritic cells. In this study, we show that NETs released by human neutrophils can directly prime T cells by reducing their activation threshold. NETs-mediated priming increases T cell responses to specific Ags and even to suboptimal stimuli, which would not induce a response in resting T cells. T cell priming mediated by NETs requires NETs/cell contact and TCR signaling, but unexpectedly we could not demonstrate a role of TLR9 in this mechanism. NETs-mediated T cell activation adds to the list of neutrophil functions and demonstrates a novel link between innate and adaptive immune responses.

Cumulative autoimmunity: T cell clones recognizing several self-epitopes exhibit enhanced pathogenicity

T cell receptor (TCR) recognition is intrinsically polyspecific. In the field of autoimmunity, recognition of both self- and microbial peptides by a single TCR has led to the concept of molecular mimicry. However, findings made by our group and others clearly demonstrate that a given TCR can also recognize multiple distinct self-peptides. Based on experimental data we argue that recognition of several self-peptides increases the pathogenicity of an autoreactive T cell; a property we refer to as “cumulative autoimmunity.” The mechanisms of such increased pathogenicity, and the implications of cumulative autoimmunity regarding the pathophysiology of T cell-mediated autoimmune diseases will be discussed.

GM-CSF production allows the identification of immunoprevalent antigens recognized by human CD4+ T cells following smallpox vaccination

The threat of bioterrorism with smallpox and the broad use of vaccinia vectors for other vaccines have led to the resurgence in the study of vaccinia immunological memory. The importance of the role of CD4+ T cells in the control of vaccinia infection is well known. However, more CD8+ than CD4+ T cell epitopes recognized by human subjects immunized with vaccinia virus have been reported. This could be, in part, due to the fact that most of the studies that have identified human CD4+ specific protein-derived fragments or peptides have used IFN-γ production to evaluate vaccinia specific T cell responses. Based on these findings, we reasoned that analyzing a large panel of cytokines would permit us to generate a more complete analysis of the CD4 T cell responses. The results presented provide clear evidence that TNF-α is an excellent readout of vaccinia specificity and that other cytokines such as GM-CSF can be used to evaluate the reactivity of CD4+ T cells in response to vaccinia antigens. Furthermore, using these cytokines as readout of vaccinia specificity, we present the identification of novel peptides from immunoprevalent vaccinia proteins recognized by CD4+ T cells derived from smallpox vaccinated human subjects. In conclusion, we describe a “T cell–driven” methodology that can be implemented to determine the specificity of the T cell response upon vaccination or infection. Together, the single pathogen in vitro stimulation, the selection of CD4+ T cells specific to the pathogen by limiting dilution, the evaluation of pathogen specificity by detecting multiple cytokines, and the screening of the clones with synthetic combinatorial libraries, constitutes a novel and valuable approach for the elucidation of human CD4+ T cell specificity in response to large pathogens.

The diversity of torque teno viruses: in vitro replication leads to the formation of additional replication-competent subviral molecules

The family Anelloviridae comprises torque teno viruses (TTVs) diverse in genome structure and organization. The isolation of a large number of TTV genomes (TTV Heidelberg [TTV-HD]) of 26 TTV types is reported. Several isolates from the same type indicate sequence variation within open reading frame 1 (ORF1), resulting in considerably modified open reading frames. We demonstrate in vitro replication of 12 full-length genomes of TTV-HD in 293TT cells. Propagation of virus was achieved by several rounds of infections using supernatant and frozen whole cells of initially infected cells. Replication of virus was measured by PCR amplification and transcription analyses. Subgenomic molecules (μTTV), arising early during propagation and ranging in size from 401 to 913 bases, were cloned and characterized. Propagation of these μTTV in in vitro cultures was demonstrated in the absence of full-length genomes.

Torque teno mini virus infection and multiple sclerosis

Multiple sclerosis (MS) is a disease of young adults which is characterized by autoimmune demyelination of the central nervous system. Interaction of genetics and environmental factors are required to cause MS. Among the proposed environmental factors for MS, viral infections are thought to play a role in the pathogenesis of the disease. Torque teno mini virus (TTMV), which has recently been shown to infect humans, is a member of circoviridae, and has a circular DNA with 2860 nucleotides. Since there are a few data about the pathogenicity of this virus, this study sought to investigate the presence of TTMV in sera from MS patients and healthy individuals. We studied 149 serum samples from MS patients and 150 sera of healthy individuals. Serum DNA was extracted using phenol-chloroform and was subjected to nested polymerase chain reaction. TTMV-DNA was detected in 24 (16%) sera of the healthy blood donors and in 21 (14.1%) samples of the MS patients, where the difference did not reach significance (p > .05). The result of this study could not establish an association between TTMV infection and MS.

Environmental triggers of multiple sclerosis

Multiple sclerosis is a chronic immune-mediated disease of the central nervous system that develops in young adults with a complex genetic predisposition. Similar to other autoimmune disease, HLA-DR and -DQ alleles within the HLA class II region on chromosome 6p21 are by far the strongest risk-conferring genes. Less robust susceptibility effects have been reported for non-MHC related genetic variants. Improvements in the design of epidemiological studies helped to identify consistent environmental risk-associations such as the increased susceptibility for MS in individuals with a history of infectious mononucleosis, a symptomatic primary infection with the human γ-herpesvirus Epstein-Barr virus (EBV). Sun exposure and serum vitamin D levels are emerging non-infectious environmental risk factors that may have independent roles. The analysis of environmental effects will likely expand in the next few years and will allow for the generation of testable hypotheses as to how environmental insults interact with genetic factors to jointly determine the susceptibility to MS. Insights gained from these studies might facilitate the development of prevention strategies and more effective treatments for MS.

Human anelloviruses and the central nervous system

Torque teno virus and related anelloviruses are a recent addition to the list of agents that cause chronic productive infections and high levels of plasma viraemia in humans. Many aspects of the natural history and pathogenesis of these under many respects surprising viruses are still poorly understood. In this review, we briefly outline the general properties of anelloviruses, examine what is currently known about the interactions they establish with the central nervous system (CNS), and discuss the possible pathological consequences.

Heterologous immunity: immunopathology, autoimmunity and protection during viral infections

Heterologous immunity is a common phenomenon present in all infections. Most of the time it is beneficial, mediating protective immunity, but in some individuals that have the wrong crossreactive response it leads to a cascade of events that result in severe immunopathology. Infections have been associated with autoimmune diseases such as diabetes, multiple sclerosis and lupus erythematosis, but also with unusual autoimmune like pathologies where the immune system appears dysregulated, such as, sarcoidosis, colitis, panniculitis, bronchiolitis obliterans, infectious mononucleosis and even chronic fatigue syndrome. Here we review the evidence that to better understand these autoreactive pathologies it requires an evaluation of how T cells are regulated and evolve during sequential infections with different pathogens under the influence of heterologous immunity.

Therapeutic approaches to multiple sclerosis: an update on failed, interrupted, or inconclusive trials of immunomodulatory treatment strategies

Multiple sclerosis (MS) continues to be a therapeutic challenge, and much effort is being made to develop new and more effective immune therapies. Particularly in the past decade, neuroimmunologic research has delivered new and highly effective therapeutic options, as seen in the growing number of immunotherapeutic agents and biologics in development. However, numerous promising clinical trials have failed to show efficacy or have had to be halted prematurely because of unexpected adverse events. Some others have shown results that are of unknown significance with regard to a reliable assessment of true efficacy versus safety. For example, studies of the highly innovative monoclonal antibodies that selectively target immunologic effector molecules have not only revealed the impressive efficacy of such treatments, they have also raised serious concerns about the safety profiles of these antibodies. These results add a new dimension to the estimation of risk-benefit ratios regarding acute or long-term adverse effects. Therapeutic approaches that have previously failed in MS have indicated that there are discrepancies between theoretical expectations and practical outcomes of different compounds. Learning from these defeats helps to optimize future study designs and to reduce the risks to patients. This review summarizes trials on MS treatments since 2001 that failed or were interrupted, attempts to analyze the underlying reasons for failure, and discusses the implications for our current view of MS pathogenesis, clinical practice, and design of future studies. In order to maintain clarity, this review focuses on anti-inflammatory therapies and does not include studies on already approved and effective disease-modifying therapies, albeit used in distinct administration routes or under different paradigms. Neuroprotective and alternative treatment strategies are presented elsewhere.

Viral triggers of multiple sclerosis

Genetic and environmental factors jointly determine the susceptibility to develop Multiple Sclerosis (MS). Collaborative efforts during the past years achieved substantial progress in defining the genetic architecture, underlying susceptibility to MS. Similar to other autoimmune diseases, HLA-DR and HLA-DQ alleles within the HLA class II region on chromosome 6p21 are the highest-risk-conferring genes. Less-robust susceptibility effects have been identified for MHC class I alleles and for non-MHC regions. The role of environmental risk factors and their interaction with genetic susceptibility alleles are much less well defined, despite the fact that infections have long been associated with MS development. Current data suggest that infectious triggers are most likely ubiquitous, i.e., highly prevalent in the general population, and that they require a permissive genetic trait which predisposes for MS development. In this review article, we illustrate mechanisms of infection-induced immunopathologies in experimental animal models of autoimmune CNS inflammation, discuss challenges for the translation of these experimental data into human immunology research, and provide future perspectives on how novel model systems could be utilized to better define the role of viral pathogens in MS.

Heterologous immunity between viruses

Immune memory responses to previously encountered pathogens can sometimes alter the immune response to and the course of infection of an unrelated pathogen by a process known as heterologous immunity. This response can lead to enhanced or diminished protective immunity and altered immunopathology. Here, we discuss the nature of T-cell cross-reactivity and describe matrices of epitopes from different viruses eliciting cross-reactive CD8(+) T-cell responses. We examine the parameters of heterologous immunity mediated by these cross-reactive T cells during viral infections in mice and humans. We show that heterologous immunity can disrupt T-cell memory pools, alter the complexity of the T-cell repertoire, change patterns of T-cell immunodominance, lead to the selection of viral epitope-escape variants, alter the pathogenesis of viral infections, and, by virtue of the private specificity of T-cell repertoires within individuals, contribute to dramatic variations in viral disease. We propose that heterologous immunity is an important factor in resistance to and variations of human viral infections and that issues of heterologous immunity should be considered in the design of vaccines.

Potential triggers of MS

MS is an immune mediated disease of the central nervous system (CNS) characterized by demyelination, axonal damage and neurologic disability. The primary cause of this CNS disease remains elusive. Here we will address our current understanding of the role of viruses as potential environmental triggers for MS. Virus infections can act peripherally (outside the CNS) or within the CNS. The association of viral infections with demyelinating disease, in both animals and humans, will be discussed, as will the potential contributions of peripheral infection with Torque Teno virus, infection outside of and/or within the CNS with Epstein-Barr virus and infection within the CNS with Human Herpesvirus 6 to MS. An experimental animal model, Theiler's murine encephalomyelitis virus infection of susceptible strains of mice is an example of viral infections of the CNS as a prerequisite for demyelination. Finally, the proposition that multiple virus infections are required, which first prime the immune system and then trigger the disease, as a model where infections outside of the CNS lead to inflammatory changes within the CNS, for the development of a MS-like disease is explored.