Detection of viral DNA and immune responses to the human herpesvirus 6 101-kilodalton virion protein in patients with multiple sclerosis and in controls

From Viral Infection to Autoimmune Reaction: Exploring the Link between Human Herpesvirus 6 and Autoimmune Diseases

The complexity of autoimmunity initiation has been the subject of many studies. Both genetic and environmental factors are essential in autoimmunity development. Among others, environmental factors include infectious agents. HHV-6 is a ubiquitous human pathogen with a high global prevalence. It has several properties suggestive of its contribution to autoimmunity development. HHV-6 has a broad cell tropism, the ability to establish latency with subsequent reactivation and persistence, and a range of immunomodulation capabilities. Studies have implicated HHV-6 in a plethora of autoimmune diseases-endocrine, neurological, connective tissue, and others-with some studies even proposing possible autoimmunity induction mechanisms. HHV-6 can be frequently found in autoimmunity-affected tissues and lesions; it has been found to infect autoimmune-pathology-relevant cells and influence immune responses and signaling. This review highlights some of the most well-known autoimmune conditions to which HHV-6 has been linked, like multiple sclerosis and autoimmune thyroiditis, and summarizes the data on HHV-6 involvement in autoimmunity development.

Human Herpesviruses 6A and 6B in Brain Diseases: Association versus Causation

Human herpesvirus 6A (HHV-6A) and human herpesvirus 6B (HHV-6B), collectively termed HHV-6A/B, are neurotropic viruses that permanently infect most humans from an early age. Although most people infected with these viruses appear to suffer no ill effects, the viruses are a well-established cause of encephalitis in immunocompromised patients. In this review, we summarize the evidence that the viruses may also be one trigger for febrile seizures (including febrile status epilepticus) in immunocompetent infants and children, mesial temporal lobe epilepsy, multiple sclerosis (MS), and, possibly, Alzheimer's disease. We propose criteria for linking ubiquitous infectious agents capable of producing lifelong infection to any neurologic disease, and then we examine to what extent these criteria have been met for these viruses and these diseases.

Search for viral agents in cerebrospinal fluid in patients with multiple sclerosis using real-time PCR and metagenomics

Multiple sclerosis (MS) is a chronic, immune-mediated demyelinating disease of the central nervous system of unclear etiology, but there is some evidence that viral infections could be responsible for triggering autoimmune mechanisms against myelin. We searched for viral RNA and DNA in cerebrospinal fluid (CSF) of 34 MS patients and 13 controls using RT-PCR/PCR against common neurotropic viruses. In addition, shotgun DNA- and RNA-based metagenomics were done in 13 MS patients and 4 controls. Specific quantitative real-time RT-PCR/PCR testing revealed the presence of viral nucleic acid in seven (20.59%) MS patients and in one (7.69%) control patient. In MS patients the most frequently detected was human herpesvirus type 6 (HHV-6; 3 cases; 8.82%); followed by Epstein-Barr virus (EBV; 2 cases; 5.88%), varicella zoster virus (VZV; 1 case; 2.94%) and Enterovirus (EV; 1 case; 2.94%). The single identified virus among controls was EBV (7.69%). DNA and RNA metagenomic assays did not identify any known eukaryotic viruses even though three of the analyzed samples were low-level positive by specific quantitative real-time PCR. In conclusion, we detected the presence of Herpesviridae and occasionally Enteroviridae in CSF from patients with MS but their prevalence was not significantly higher than among controls. Metagenomic analysis seems to be less sensitive than real-time RT-PCR/PCR and it did not detect any potential viral pathogens.

Relationship of human herpes virus 6 and multiple sclerosis: A systematic review and meta-analysis

Infection with human herpes viruses has been suggested to contribute to multiple sclerosis (MS), while interaction between human herpes 6 (HHV6) and MS remain unclear yet. Here, we conducted a meta-analysis on the relationship of HHV6 infection and MS. All related studies were collected from major databases. The analyses were performed by STATA 14 and Comprehensive Meta-Analysis V2.0 softwares. Pooled odds ratios (ORs) and 95%CIs were calculated from the raw data of the including studies by the random effects models when I2 > 50% and fix model when I2 < 50%. Thirty nine studies were included in the meta-analysis that 34 studies used molecular assays and 7 studies used serological assays for diagnosis of HHV6 infected cases. The relationship of HHV6 and MS was significant in healthy control group by yielding a summary OR of (2.23 [1.5-3.3], p = 0.06). A significant HHV6 association with MS were in the studies with >6 score that used serum/blood sample with OR of (6.7 [95%CI 4.8-8.6], p < 0.00001) and in serological studies, IgM positive titer in other neurological diseases (OND) control group was significant with OR of (8.3 [95%CI 3-24.07], p < 0.00001). This study has been showed that there were significant relationship between MS and HHV6 infection.

Cytokine and cellular responses to human herpesvirus-6B in patients with B-acute lymphoblastic leukemia

Primary infection with human herpesvirus-6 (HHV-6), is followed by its lifelong persistence in the host. Most T-cell responses to HHV-6 have been characterized using peripheral blood from healthy adults; however, the role of HHV-6 infection in immune modulation has not been elucidated for some diseases. Therefore, in this study the immune response to HHV-6 infection in patients with B-acute lymphoblastic leukemia (B-ALL) was analyzed. HHV-6 load was quantified in blood samples taken at the time of diagnosis of leukemia and on remission. The same concentrations of anti- and pro-inflammatory cytokines (IL-4, IL-1, IL-6, IL-8, IL-12p70, IL-17a, TNF-α and IFN-γ) were detected in plasma samples from 20 patients with and 20 without detectable HHV-6 virus loads in blood. Characterization of T-cell responses to HHV-6 showed low specific T-cells frequencies of 2.08% and 1.46% in patients with and without detectable viral loads, respectively. IFN-γ-producing T cells were detected in 0.03%-0.23% and in 0%-0.2% of CD4+T cells, respectively. Strong production of IL-6 was detected in medium supernatants of challenged T-cells whatever the HHV-6 status of the patients (973.51 ± 210.06 versus 825.70 ± 210.81 pg/mL). However, concentrations of TNF-α and IFN-γ were low. Thus, no association between plasma concentrations of cytokines and detection of HHV-6 in blood was identified, suggesting that HHV-6 is not strongly associated with development of B-ALL. The low viral loads detected may correspond with latently infected cells. Alternatively, HHV-6B specific immune responses may be below the detection threshold of the assays used.

Virus-Induced Demyelination: The Case for Virus(es) in Multiple Sclerosis

Multiple Sclerosis (MS) is the most common demyelinating disease of man with over 400,000 cases in the United States and over 2.5 million cases worldwide. There are over 64,000 citations in Pubmed dating back as far as 1887. Much has been learned over the past 129 years with a recent burst in therapeutic options (mostly anti-inflammatory) with newer medications in development that are neuroprotective and/or neuroreparative. However, with all these advancements the cause of MS remains elusive. There is a clear interplay of genetic, immunologic, and environmental factors that influences both the development and progression of this disorder. This chapter will give a brief overview of the history and pathogenesis of MS with attention to how host immune responses in genetically susceptible individuals contribute to the MS disease process. In addition, we will explore the role of infectious agents in MS as potential “triggers” of disease. Models of virus-induced demyelination will be discussed, with an emphasis on the recent interest in human herpesviruses and the role they may play in MS disease pathogenesis. Although we remain circumspect as to the role of any microbial pathogen in MS, we suggest that only through well-controlled serological, cellular immune, molecular, and animal studies we will be able to identify candidate agents. Ultimately, clinical interventional trials that either target a specific pathogen or class of pathogens will be required to make definitive links between the suspected agent and MS.

Identification of novel CD8+ T cell epitopes in human herpesvirus 6B U11 and U90

Human herpesvirus 6B (HHV6B) infects over 90% of the population, and normally establishes a latent infection, where episodes of reactivation are asymptomatic. However, in immunocompromised patients HHV6B reactivation is associated with high morbidity and mortality. Cellular immunotherapy has been utilised against other herpesvirus in immunocompromised settings. However, limited information on the immune response against HHV6B has hampered the development of immunotherapy for HHV6B-driven disease. In this study, we have analysed the cellular immune response against four HHV6B antigens in a panel of 30 healthy donors. We show that the base-line level of T cell reactivity in peripheral blood is very low to undetectable. A short-term reactivation step enabled expansion of T cell responses, and all donors responded to at least 1 antigen, but more commonly 3 or 4. A hierarchy of immunogenicity was determined with antigens U90 and U54 being co-dominant, followed by U11 and U39. Putative CD8+ T cell epitopes were mapped to U90 and U11, predicted to be presented in the context of HLA-A1, A29, B39 and C6. T cells reactive against these novel epitopes were able to recognise virus-infected cells. Our data is supportive of the application and on-going development of T cell immunotherapy against HHVB-driven disease in the immunocompromised host.

Immune response to HHV-6 and implications for immunotherapy

Most adults remain chronically infected with HHV-6 after resolution of a primary infection in childhood, with the latent virus held in check by the immune system. Iatrogenic immunosuppression following solid organ transplantation (SOT) or hematopoetic stem cell transplantation (HSCT) can allow latent viruses to reactivate. HHV-6 reactivation has been associated with increased morbidity, graft rejection, and neurological complications post-transplantation. Recent work has identified HHV-6 antigens that are targeted by the CD4+ and CD8+ T cell response in chronically infected adults. T cell populations recognizing these targets can be expanded in vitro and are being developed for use in autologous immunotherapy to control post-transplantation HHV-6 reaction.

Identification of the major HHV-6 antigen recognized by cerebrospinal fluid IgG in multiple sclerosis

BACKGROUND AND PURPOSE

Different data show an association between human herpesvirus 6 (HHV-6) and multiple sclerosis (MS). Intrathecal anti-HHV-6 immunoglobulin G (IgG) was detected in MS patients, but the antigen recognized by cerebrospinal fluid (CSF) IgG has not been characterized yet. Our objective was to identify the HHV-6 antigens recognized by IgG present in the CSF of patients with MS.

METHODS

Cerebrospinal fluid IgG of 15 MS patients and eight patients with other neurological diseases was purified on protein G Sepharose columns. Purified IgG from every patient was linked to a CNBr-activated Sepharose 4B column. Fifty micrograms of viral extract was applied to each column. Bound proteins were eluted and analysed by SDS-PAGE and silver staining. The viral protein was characterized by mass spectrometry.

RESULTS

A protein of 150 kD was eluted from CSF IgG columns of three of eight patients with primary progressive MS and one of seven with relapsing-remitting MS. After digestion and mass spectrometry analysis 10 peptides were found with 100% homology with the major capsid protein of the HHV-6A.

DISCUSSION

These findings confirm the presence of anti-HHV-6 IgG in CSF of MS patients, particularly in progressive forms, and identify major capsid protein as the major antigen recognized by CSF IgG from MS patients.

Prevalence of human Herpesviridae in cerebrospinal fluid of patients with multiple sclerosis and noninfectious neurological disease in the Netherlands

Prevalence of eight human herpesviruses (HHV1-8) was determined by real-time PCR in cell-rich cerebrospinal fluid (CSF) samples, obtained early after disease symptoms, of Dutch patients with multiple sclerosis (MS) and other noninfectious central nervous system diseases (NIND). Whereas HHV1-8 DNA was undetectable in CSF samples of MS patients, HHV6 DNA was detected in a plexus neuritis case and HHV7 DNA in an ependymoma and a Behçets' disease patient. However, intrathecal HHV infection was not detected. Data indicate that HHV1-8 are rarely detected in CSF of Dutch NIND patients and do not support the role of intrathecal HHV infection early after onset of disease symptoms in MS.

HHV-6 and Multiple Sclerosis

Multiple sclerosis (MS) is an inflammatory demyelinating disease affecting the central nervous system, thought to be an autoimmune disease mediated by autoreactive lymphocytes. The pathogenesis of MS is multifactorial and is thought to be triggered by multiple environmental factors in genetically susceptible individuals. Viruses have long been postulated as potential environmental triggers in MS, and there is increasing evidence of a link between viruses and MS. Some of the most compelling data have been found in human herpesvirus 6 (HHV-6) research. HHV-6 is a ubiquitous, neurotropic herpesvirus; HHV-6 DNA has been found in MS plaques compared to healthy brain tissue. Studies have also shown that MS patients have higher viral titers and higher DNA detection in serum and CSF compared to controls, and that the virus seems to be more actively replicating in MS patients. Potential mechanisms for HHV-6 leading to autoimmunity include molecular mimicry, bystander activation, and epitope spreading, among others.

Viruses and multiple sclerosis

Multiple sclerosis (MS) is a heterogeneous disease that develops as an interplay between the immune system and environmental stimuli in genetically susceptible individuals. There is increasing evidence that viruses may play a role in MS pathogenesis acting as these environmental triggers. However, it is not known if any single virus is causal, or rather several viruses can act as triggers in disease development. Here, we review the association of different viruses to MS with an emphasis on two herpesviruses, Epstein-Barr virus (EBV) and human herpesvirus 6 (HHV-6). These two agents have generated the most impact during recent years as possible co-factors in MS disease development. The strongest argument for association of EBV with MS comes from the link between symptomatic infectious mononucleosis and MS and from seroepidemiological studies. In contrast to EBV, HHV-6 has been found significantly more often in MS plaques than in MS normal appearing white matter or non-MS brains and HHV-6 re-activation has been reported during MS clinical relapses. In this review we also suggest new strategies, including the development of new infectious animal models of MS and antiviral MS clinical trials, to elucidate roles of different viruses in the pathogenesis of this disease. Furthermore, we introduce the idea of using unbiased sequence-independent pathogen discovery methodologies, such as next generation sequencing, to study MS brain tissue or body fluids for detection of known viral sequences or potential novel viral agents.

Immunotherapeutic strategies to prevent and treat human herpesvirus 6 reactivation after allogeneic stem cell transplantation

Human herpesvirus (HHV) 6 causes substantial morbidity and mortality in the immunocompromised host and has no approved therapy. Adoptive transfer of virus specific T cells has proven safe and apparently effective as prophylaxis and treatment of other virus infections in immunocompromised patients; however, extension to subjects with HHV6 has been hindered by the paucity of information on targets of cellular immunity. We now characterize the cellular immune response from 20 donors against 5 major HHV6B antigens predicted to be immunogenic and define a hierarchy of immunodominance of antigens based on the frequency of responding donors and the magnitude of the T-cell response. We identified specific epitopes within these antigens and expanded the HHV6 reactive T cells using a GMP-compliant protocol. The expanded population comprised both CD4(+) and CD8(+) T cells that were able to produce multiple effector cytokines and kill both peptide-loaded and HHV6B wild-type virus-infected target cells. Thus, we conclude that adoptive T-cell immunotherapy for HHV6 is a practical objective and that the peptide and epitope tools we describe will allow such cells to be prepared, administered, and monitored in human subjects.

Specific CD8⁺ T cells recognize human herpesvirus 6B

The importance of human herpesvirus 6 (HHV-6) species as human pathogens is increasingly appreciated. However, we do not understand how infection is controlled in healthy virus carriers, and why control fails in patients with disease. Other persistent viruses are under continuous surveillance by antigen-specific T cells, and specific T-cell repertoires have been well characterized for some of them. In contrast, knowledge on HHV-6-specific T-cell responses is limited, and missing for CD8(+) T cells. Here we identify CD8(+) T-cell responses to HHV-6B, the most widespread HHV-6 species, in healthy virus carriers. HHV-6B-specific CD8(+) T-cell lines and clones recognized HLA-A2-restricted peptides from the viral structural proteins U54 and U11, and displayed various antigen-specific antiviral effector functions. These CD8(+) T cells specifically recognized HHV-6B-infected primary CD4(+) T cells in an HLA-restricted manner, produced antiviral cytokines, and killed infected cells, whereas HHV-6A-infected cells were not recognized. Thus, HHV-6B-specific CD8(+) T cells are likely to contribute to control of infection, overcoming the immunomodulatory effects exerted by the virus. Potentially, HHV-6-associated disease could be addressed by active or passive immunotherapy that reconstitutes virus-specific CD8(+) T-cell responses.

Human CD4+ T cell response to human herpesvirus 6

Following primary infection, human herpesvirus 6 (HHV-6) establishes a persistent infection for life. HHV-6 reactivation has been associated with transplant rejection, delayed engraftment, encephalitis, muscular dystrophy, and drug-induced hypersensitivity syndrome. The poor understanding of the targets and outcome of the cellular immune response to HHV-6 makes it difficult to outline the role of HHV-6 in human disease. To fill in this gap, we characterized CD4 T cell responses to HHV-6 using peripheral blood mononuclear cell (PBMC) and T cell lines generated from healthy donors. CD4(+) T cells responding to HHV-6 in peripheral blood were observed at frequencies below 0.1% of total T cells but could be expanded easily in vitro. Analysis of cytokines in supernatants of PBMC and T cell cultures challenged with HHV-6 preparations indicated that gamma interferon (IFN-γ) and interleukin-10 (IL-10) were appropriate markers of the HHV-6 cellular response. Eleven CD4(+) T cell epitopes, all but one derived from abundant virion components, were identified. The response was highly cross-reactive between HHV-6A and HHV-6B variants. Seven of the CD4(+) T cell epitopes do not share significant homologies with other known human pathogens, including the closely related human viruses human herpesvirus 7 (HHV-7) and human cytomegalovirus (HCMV). Major histocompatibility complex (MHC) tetramers generated with these epitopes were able to detect HHV-6-specific T cell populations. These findings provide a window into the immune response to HHV-6 and provide a basis for tracking HHV-6 cellular immune responses.

Herpesvirus active replication in multiple sclerosis: a genetic control?

Although the etiology of multiple sclerosis (MS) is unknown, it is generally believed that genetic, immunologic, and environmental factors are involved. The objectives of this study were: 1. to analyze if a genetic control could explain why HHV-6 would be able to actively replicate in a subset of MS patients but not in controls; 2. to study if MS patients with HHV-6 active replication are clinically different from those without HHV-6 active replication. A total of 195 MS patients and 195 controls were analyzed for two SNPs at the MHC2TA locus and two SNPs at the CD46 locus. Furthermore, the MS cohort was analyzed by PCR for the detection of HHV-6 genomes in five serum samples collected every six months along two-year follow-up. We found that 59/195 (30.2%) MS patients had at least one HHV-6 positive serum sample. No statistical significant difference was found for the two genes when the comparison was made between MS patients and controls; however, a statistical significance was found for the two polymorphisms of MHC2TA when we compared MS patients with active replication and controls (p=0.0000004 for rs4774C and p=0.011 for rs3087456G). Furthermore, increased significant differences were found for MHC2TA and CD46 when we compared interferon beta responders and non-responders within MS patients. In conclusion, we describe a gene-environment interaction in MS patients between HHV-6 and MHC2TA and CD46 that should be further studied to clarify if that interaction could be a genetic control. The results show that MS patients without HHV-6 active replication are better responders to interferon beta treatment than those with HHV-6 active replication.

The human microbiome in multiple sclerosis: pathogenic or protective constituents?

The human microbiome is comprised of commensal and pathogenic microorganisms, which exert diverse effects in close proximity to the site of intection as well as in remote tissues through immune-mediated mechanisms. Multiple infectious agents have been implicated in the pathogenesis of multiple sclerosis (MS) with variable findings depending on the agent, techniques, and disease phenotype. Herein, the contributions of individual infectious agents to MS and their effects on the immune and nervous systems are reviewed, focusing on herpes viruses, coronaviruses, retroviruses, and synchronic infections. While infectious agents are often assumed to be pathogenic, their effects might also be beneficial to the host in the long-term, depending on age and the type of immunogen/pathogen exposure, as proposed by the hygiene hypothesis. The human microbiome has potential impact on future diagnostic and therapeutic issues in MS.

Human herpesvirus 6 infection as a trigger of multiple sclerosis

We systematically reviewed the existing evidence to determine whether a relationship exists between infection with human herpesvirus 6 (HHV-6) and multiple sclerosis (MS) and, if so, to define the strength of that relationship. The following terms were used in searches of the Entrez-PubMed database (1966-2009): human herpes virus 6, HHV 6, demyelination, multiple sclerosis, pathogenesis, diagnosis, serology, cerebrospinal fluid, IgG antibodies, IgM antibodies, PCR, and lymphoproliferative techniques. Study quality was assessed using the criteria proposed by Moore and Wolfson and by the classification criteria used by the Canadian Task Force on the Periodic Health Examination. Studies were categorized both by experimental technique and by quality (high [A], intermediate [B], and low [C]) as determined by the Moore and Wolfson criteria. Overall, 25 (41%) of 61 studies, 15 (60%) of which were classified as A quality, reached a statistically significant result. According to the Canadian Task Force classification, all studies were categorized as evidence of quality II-1. Limitations of the available experimental techniques and perspectives for future research are discussed. The current review supports the need for further, objective, evidence-based examination of the relationship between HHV-6 infection and multiple sclerosis.

Association between human herpesvirus 6 and occurrence of multiple sclerosis among Jordanian patients

OBJECTIVES

Multiple sclerosis (MS) is hypothesized to be caused by an infectious agent that initiates an autoimmune reaction. Among the infectious agents linked to MS is human herpesvirus 6 (HHV-6). Due to the high occurrence of MS among Jordanian population and the deficiency of MS studies in Jordan, the prevalence of HHV-6 in sera and cerebrospinal fluids (CSFs) of 36 MS patients was investigated.

MATERIALS AND METHODS

To increase the sensitivity of detection, nested polymerase chain reaction was utilized.

RESULTS

Although we were able to detect HHV-6 DNA in serum samples of 26% MS patients, no significant difference was found when compared to control individuals. In addition, lack of association between MS and presence of viral DNA in CSF samples was observed. Even within the analyzed MS patient population, an association of HHV-6 and MS in terms of gender, type of diagnosis, symptoms and disease score was not identified among Jordanian patients.

CONCLUSIONS

Although these results indicate lack of apparent association between HHV-6 to MS among Jordanian patients, heterogeneity related to genetic polymorphism as well as geographical distribution of the disease and of pathogens may be of significance.

Human herpes virus 6B: a possible role in epilepsy?

Human herpes virus 6 (HHV6) infection is nearly ubiquitous in childhood and may include central nervous system invasion. There are two variants, HHV6A and HHV6B. Usually asymptomatic, it is associated with the common, self-limited childhood illness roseola infantum and rarely with more severe syndromes. In patients with immune compromise, subsequent reactivation of viral activity may lead to severe limbic encephalitis. HHV6 has been identified as a possible etiologic agent in multiple sclerosis, myocarditis, and encephalitis. A preponderance of evidence supports an association between HHV6 and febrile seizures. An ongoing multicenter study is investigating possible links between HHV6 infection, febrile status epilepticus, and development of mesial temporal sclerosis (MTS). Investigation of temporal lobectomy specimens showed evidence of active HHV6B but not HHV6A replication in hippocampal astrocytes in about two-thirds of patients with MTS but not other causes of epilepsy. It has been suggested that HHV6B may cause "excitotoxicity" by interfering with astrocyte excitatory amino acid transport. Although conventional inflammatory changes are not found in most MTS specimens, inflammatory modulators may play a role in neuronal injury leading to MTS as well. If the link between early viral infection, complex or prolonged febrile seizures, and later development of intractable temporal lobe epilepsy is confirmed, new therapeutic approaches to a common intractable epilepsy syndrome may be possible.

Herpesviruses and human endogenous retroviral sequences in the cerebrospinal fluid of multiple sclerosis patients

OBJECTIVE

To analyze the possible role of human herpesvirus (HHVs) and human endogenous retroviruses (HERVs) infection in multiple sclerosis (MS) pathogenesis.

METHODS

A total of 92 cerebrospinal fluid (CSF) samples were collected: 48 from MS patients at the first clinically evident demyelinating event, 23 from patients with other inflammatory neurological diseases (OINDs) and 21 from patients with other non-inflammatory neurological diseases (ONINDs). Total DNA and RNA were isolated, and the prevalences and viral loads of herpes simplex virus (HSV), varicella-zoster virus (VZV), Epstein-Barr virus (EBV), cytomegalovirus (CMV), HHV-6, HERV-H and HERV-W in the CSF of MS patients and controls were evaluated using a quantitative real-time polymerase chain reaction assay.

RESULTS

(i) For HSV, 1/48 (2.1%, 86 copies/ml of CSF) MS patients and 1/23 (4.3%, 115.2 copies/ml of CSF) OIND patients (a myelitis case) had HSV sequences in the CSF; (ii) for EBV, only 1/48 (2.1%, 72 copies/ml of CSF) MS patients was positive for EBV; (iii) for HHV-6, only 5/48 (10.4%) MS patients had HHV-6 genomes in their CSF (128.1 copies/ml of CSF); (iv) we did not find any positive cases for VZV, CMV, HERV-H and HERV-W among MS patients or controls; (v) no cases of co-infections were found; (vi) the whole prevalence of HHVs was 7/48 (14.6%) for MS patients and 1/44 (2.3%) for controls (p = 0.038).

CONCLUSION

The findings described here show that HHV infection is more frequent in the CSF of MS patients than in patients with other neurological diseases; however, only HHV-6 seems to be involved in the pathogenesis of MS in a subset of patients.

Varicella-zoster virus at relapses of multiple sclerosis

The possible participation of different herpes viruses was studied during exacerbations of multiple sclerosis (MS). We searched for the presence of DNA from the following herpes viruses: varicella zoster virus (VZV), herpes-simplex viruses 1 and 2; Epstein-Barr virus (EBV) and human herpes-virus-6 (HHV6) in mononuclear cells from patients with MS during relapse (n = 40), MS during remission (n = 131) and controls (n = 125). Additionally, immune cells containing viral antigens were quantified by flow cytometry, and VZV load was determined by real time PCR in 2 MS patients at various times during relapse and remission. DNA from VZV was found in 95% of MS patients during relapse and in 17% during remission; all controls were negative; by contrast, DNA from HHV6 was found in 24% of MS patients during relapse and in 2% during remission; DNA from herpes simplex viruses was not found in any subject; and DNA from EBV was found in a similar percentage of subjects from all groups. Sequential quantification of VZV-load showed a curve that increased during relapse and disappeared at remission. Also, VZV antigens were found inside a large number of immune cells from MS patients during relapse as compared with MS patients on remission and controls. In the typical forms of VZV infection, varicella and herpes-zoster, DNA from VZV is found in mononuclear cells exclusively during brief periods at the beginning of the active infection, but not during latency; thus, the conspicuous presence of VZV during relapses of MS may indicate a period of active infection and suggests the participation of VZV in the pathogenesis of MS.

JC virus in cerebrospinal fluid samples of multiple sclerosis patients at the first demyelinating event

Objective To evaluate the possible involvement of JC virus (JCV) in the aetiology of multiple sclerosis (MS), through the comparison of DNA prevalences and viral loads of JCV in cerebrospinal fluid (CSF) of MS patients at the first demyelinating event and subjects suffering from other neurological diseases (OND).

Methods Seventy-three CSF samples (43 from MS patients at the first demyelinating event, and 30 from patients with OND) were collected; all MS cases were followed up from 1 to 6.7 years after they were diagnosed with clinically definite MS. DNA was extracted and analysed by real-time PCR for the detection of JCV genomes.

Results We found JCV DNA in the CSF of two MS patients (4.7%) with a mean viral load of 2.1 and 6.7 copies/mL of CSF. Among the patients of the OND group we did not find any positive sample. We did not find any difference in the course of the disease between MS patients with and without JCV genomes in their CSF along the follow up.

Conclusion JCV seems to be only a bystander in the pathology of MS, and the presence of cell-free viral particles could be related to the immunological activation of the disease, mainly during relapses. Multiple Sclerosis 2007; 13: 590-595. http://msj.sagepub.com

Virus-mediated autoimmunity in Multiple Sclerosis

Epidemiological data suggest the notion that in Multiple Sclerosis (MS) is an acquired autoimmune disease and the cause may be an environmental factor(s), probably infectious, in genetically susceptible individuals. Several cases of viral induced demyelinatimg encephalomyelitis in human beings and in experimental models as well as the presence of IgG oligoclonal bands in the cerebrospinal fluid indicate that the infectious factor may be viral. However, the absence of a specific virus identification in MS central nervous system may hardly support this notion. On the other hand, the partial response of patients with MS to immunosuppressive and immunomodulatory therapy support the evidence of an autoimmune etiology for MS. However, the autoimmune hypothesis shares the same criticism with the infectious one in that no autoantigen(s) specific to and causative for MS has ever been identified. Nevertheless, the absence of identifiable infectious agent, especially viral does not rule out its presence at a certain time – point and the concomitant long term triggering of an autoimmune cascade of events thereafter. Several concepts have emerged in an attempt to explain the autoimmune mechanisms and ongoing neurodegeneration in MS on the basis of the infectious – viral hypothesis.

Human herpesvirus 6 (HHV-6) U94/REP protein inhibits betaherpesvirus replication

Human herpesvirus 6 (HHV-6) is the only human herpesvirus encoding U94/rep, homologue to the parvovirus non-structural gene rep68/78. Results to date suggest that HHV-6 U94/rep might regulate viral gene expression and have a role in viral latency. To determine the effect of U94/REP upon viral replication, the protein was produced. The purified U94/REP retained the characteristic immunological features. It was internalized and localized in the nucleus of human cells, showing marked inhibitory activity on the replication of HHV-6 (both variants A and B). The effect of U94/REP was dose-dependent and sensitive to treatment with single-stranded but not double-stranded DNA. U94/REP inhibited the replication of other betaherpesviruses, HHV-7 and human cytomegalovirus, but had no effect on herpes simplex virus. These results confirm the action of U94/rep latency gene in the regulation of HHV-6 replication with implications for co-reactivations and latency of human betaherpesviruses.

Co-purification of soluble membrane cofactor protein (CD46) and human herpesvirus 6 variant A genome in serum from multiple sclerosis patients

The association of human herpesvirus 6 (HHV-6) and multiple sclerosis (MS) has been supported by several immunological and molecular studies. Recently, membrane cofactor protein (CD46) has been identified as the cellular receptor for the A and B variants of HHV-6. Elevated levels of soluble CD46 (sCD46) have been reported in the serum and CSF of MS patients. The aim of this study was to investigate a possible correlation between elevated levels of soluble CD46 and the presence of serum HHV-6 DNA in MS patients. An immunoaffinity column comprised of immobilized monoclonal antibodies to CD46 was developed to isolate sCD46 from cell free body fluids of MS patients and controls. After immunoaffinity purification, DNA was extracted from anti-CD46 column eluates and subjected to PCR amplification. Of the 42 MS samples tested, 4 serum samples were HHV-6 positive, 3 of which were typed as HHV-6A. The co-purification of sCD46 and HHV-6 DNA from MS sera indicates that HHV-6 is tightly connected to its receptor, CD46, in the serum of MS patients.

Distribution and quantification of human herpesvirus 6 in multiple sclerosis and control brains

Multiple sclerosis (MS) is thought to be precipitated by environmental factors, potentially including viruses, in genetically susceptible individuals and recently human herpesvirus 6 (HHV-6) has been associated with the disease. We have analysed post mortem brain for the presence, variant type and quantity of HHV-6 by PCR. A total of 124 samples from seven anatomically defined regions of brain were tested from MS cases and controls. HHV-6 DNA was detected in 41% and 44% of MS case and control samples. The median viral loads were 11 and 9 genome copies/microg DNA in cases and controls respectively and the viral load was not increased in lesions. Except in one instance, the HHV-6 DNA detected was variant B. There was no apparent difference in the distribution of HHV-6 DNA in the brains of MS cases versus controls, nor between normal appearing and lesional tissue in MS cases. Periventricular regions of the brain were more frequently positive for HHV-6 DNA in both MS cases and controls, although this difference was not statistically significant. These studies confirm the neurotropism of HHV-6 but do not demonstrate differences in the distribution, variant type or quantity of HHV-6 in brains from patients with MS versus controls.

Early and late HHV-6 gene transcripts in multiple sclerosis lesions and normal appearing white matter

Multiple sclerosis is an inflammatory demyelinating disease of the CNS, the aetiology of which is believed to have both genetic and environmental components. We have investigated one of the candidate viruses for the environmental component of multiple sclerosis, the neurotropic human herpesvirus 6 (HHV-6). Utilizing fluorescent in situ hybridization (FISH) techniques, we have examined human post-mortem tissues for the presence of immediate early and late viral gene expression in multiple sclerosis patient normal appearing white matter (NAWM), lesional tissue and normal control brain samples. HHV-6 gene transcription was detected in all tissue samples and was restricted to oligodendrocytes, as determined by double mRNA FISH analysis. Quantitative analysis of viral mRNA expression indicated that both NAWM and lesional multiple sclerosis samples exhibited significantly higher levels of HHV-6 expression compared with the normal control samples. Lesional samples exhibited the highest levels of viral gene expression, with NAWM exhibiting an intermediate level between lesional and control tissues. Immunofluorescence against early and late HHV-6 proteins verified active translation of HHV-6 viral mRNA in oligodendrocytes. Southern blot analysis of nested polymerase chain reactions using extracted genomic DNA and cDNA confirmed the presence of the HHV-6 genome in all individuals, with the active expression profile mirroring the FISH results. The frequent high level of HHV-6 infection in multiple sclerosis samples suggests a possible role in pathogenesis.

Update on human herpesvirus 6 biology, clinical features, and therapy

Human herpesvirus 6 (HHV-6) is a betaherpesvirus that is closely related to human cytomegalovirus. It was discovered in 1986, and HHV-6 literature has expanded considerably in the past 10 years. We here present an up-to-date and complete overview of the recent developments concerning HHV-6 biological features, clinical associations, and therapeutic approaches. HHV-6 gene expression regulation and gene products have been systematically characterized, and the multiple interactions between HHV-6 and the host immune system have been explored. Moreover, the discovery of the cellular receptor for HHV-6, CD46, has shed a new light on HHV-6 cell tropism. Furthermore, the in vitro interactions between HHV-6 and other viruses, particularly human immunodeficiency virus, and their relevance for the in vivo situation are discussed, as well as the transactivating capacities of several HHV-6 proteins. The insight into the clinical spectrum of HHV-6 is still evolving and, apart from being recognized as a major pathogen in transplant recipients (as exemplified by the rising number of prospective clinical studies), its role in central nervous system disease has become increasingly apparent. Finally, we present an overview of therapeutic options for HHV-6 therapy (including modes of action and resistance mechanisms).

Beta-Interferon Treatment Reduces Human Herpesvirus-6 Viral Load in Multiple Sclerosis Relapses but Not in Remission

To determine whether the DNA prevalence of human herpesvirus-6 (HHV-6), the viral load and the prevalence of both HHV-6 variants in relapsing-remitting multiple sclerosis (RRMS) patients in exacerbation are altered by beta-interferon (IFN-beta) treatment, in comparison with RRMS patients in remission, we analyzed HHV-6 (A and B) genomes in 189 serum samples by quantitative real-time polymerase chain reaction: 105 of the RRMS patients were receiving IFN-beta treatment (48 in exacerbation) and 84 were untreated (36 in relapse). The results were as follows. (1) Prevalence decrease because of IFN-beta treatment was not significant: 25% of RRMS patients in relapse vs. 15.9% in remission (p = 0.45). (2) Viral load was twice as much in untreated patients in relapse than in treated ones. (3) We only found variant A. Since IFN-beta treatment is able to significantly reduce HHV-6 viral load in RRMS patients in relapse, but not in remission, we suggest a role for HHV-6 in the pathogenesis of multiple sclerosis exacerbations and an antiviral role for IFN-beta treatment in RRMS.

Increased CD8+ cytotoxic T cell responses to myelin basic protein in multiple sclerosis

Autoreactive T cells of CD4 and CD8 subsets recognizing myelin basic protein (MBP), a candidate myelin autoantigen, are thought to contribute to and play distinct roles in the pathogenesis of multiple sclerosis (MS). In this study we identified four MBP-derived peptides that had high binding affinity to HLA-A2 and HLA-A24 and characterized the CD8(+) T cell responses and their functional properties in patients with MS. There were significantly increased CD8(+) T cell responses to 9-mer MBP peptides, in particular MBP(111-119) and MBP(87-95) peptides that had high binding affinity to HLA-A2, in patients with MS compared with healthy individuals. The resulting CD8(+) T cell lines were of the Th1 phenotype, producing TNF-alpha and IFN-gamma and belonged to a CD45RA(-)/CD45RO(+) memory T cell subset. Further characterization indicated that the CD8(+) T cell lines obtained were stained with MHC class I tetramer (HLA-A2/MBP(111-119)) and exhibited specific cytotoxicity toward autologous target cells pulsed with MBP-derived peptides in the context of MHC class I molecules. These cytotoxic CD8(+) T cell lines derived from MS patients recognized endogenously processed MBP and lysed COS cells transfected with genes encoding MBP and HLA-A2. These findings support the potential role of CD8(+) CTLs recognizing MBP in the injury of oligodendrocytes expressing both MHC class I molecules and MBP.

Human herpesvirus 6 infection of the central nervous system

Human herpesvirus (HHV) 6 infects all children, usually during the first year of life. High fever is the hallmark of primary infection, with febrile seizures the most common complication. After primary infection, HHV-6 remains latent or persistent at multiple sites, with intermittent reactivation. Many disorders of the central nervous system (CNS) have been linked to HHV-6 reactivation, including chronic seizure disorders, encephalitis, and demyelinating disorders including multiple sclerosis. Although multiple studies have pieced together an understanding of the molecular organization, viral characteristics, immunology, and epidemiology of HHV-6, the true role of this virus in diseases of the CNS is still unfolding.

Human herpesvirus type 6 indirectly enhances oligodendrocyte cell death

Accumulating evidence suggests that human herpesvirus type 6 (HHV-6) plays a pathogenic role in diseases of the central nervous system including multiple sclerosis (MS). Recent studies have indicated that HHV-6 DNA is detected with high frequency in MS lesions compared to normal-appearing white matter, implicating a role for HHV-6 in MS pathogenesis. It appears that T cells, which infiltrate into the brain in MS patients, and resident oligodendrocytes harbor HHV-6 virus in MS lesions. Because T cells infected with HHV-6 have elevated proinflammatory gene expression, we hypothesized that HHV-6 could be indirectly cytotoxic to glial cells, including oligodendrocytes. Supernatants from SupT1 cells infected with HHV-6 variant A (GS or U1102) or variant B (Z29) significantly reduced MO3.1 cell proliferation by 75% +/- 10%, 78% +/- 8% or 51% +/- 9%, respectively. HHV-6 viral supernatants (GS or U1102 or Z29) significantly increased MO3.1 or primary human oligodendrocyte precursor cells (OPCs) cell death, whereas primary human fetal astrocytes were not affected. Removal of HHV-6 virions or proteins by trypsin treatment from culture supernatants did not reverse the loss in oligodendrocyte proliferation or viability. Supernatants from HHV-6 GS or U1102 cultures were significantly more cytotoxic to MO3.1 cells or OPCs compared to supernatants from T cells infected with Z29. Dying oligodendrocytes did not have an apoptotic-like phenotype and toxicity was not inhibited by general inhibitor of apoptosis, ZVAD. Further, oligodendrocytes had minimal caspase-3 activation even in the presence of staurosporine, suggesting that cell death followed caspase-independent pathways. These results indicate that HHV-6 is indirectly cytotoxic to oligodendrocytes and that cell death is driven primarily by caspase-independent pathways.

Infectious agents and multiple sclerosis--are Chlamydia pneumoniae and human herpes virus 6 involved?

A good deal of evidence suggests an infectious component in the development of multiple sclerosis (MS) and, to date, some 20 bacteria and viruses have been associated with the disease. Recent independent sets of studies have implicated the respiratory bacterium Chlamydia pneumoniae and human herpes virus 6 (HHV-6) in the pathogenesis of MS. However, as is the case for essentially all earlier microbial associations, experimental evidence linking either this bacterium or this virus to MS is equivocal. We review the published reports concerning involvement of C. pneumoniae and HHV-6 in MS, and data relating to possession of the APOE epsilon 4 allele, which some studies indicate might influence how these or other pathogens affect disease genesis. Based on the large set of inconsistent observations available and given important new information regarding the neuropathology of MS, we contend that no conclusion is possible at this point regarding the potential role of either C. pneumoniae or HHV-6 in MS. We therefore propose future studies that should clarify whether, and if so how, these and other organisms function in the pathogenesis of this disease.

Cross-reactivity with myelin basic protein and human herpesvirus-6 in multiple sclerosis

Viral infections are though to play an important role in the pathogenesis of multiple sclerosis (MS) potentially through molecular mimicry. An identical sequence was found in both myelin basic protein (MBP, residues 96-102), a candidate autoantigen for MS, and human herpesvirus-6 (HHV-6 U24, residues 4-10) that is a suspected viral agent associated with MS. In this study, we showed that greater than 50% of T cells recognizing MBP(93-105) cross-reacted with and could be activated by a synthetic peptide corresponding to residues 1 to 13 of HHV-6 U24 in MS patients. The estimated precursor frequency of these cross-reactive T cells recognizing both peptides, MBP(93-105) and HHV-6 (U24)(1-13), was significantly elevated in MS patients compared with that in healthy controls. These cross-reactive CD4+ T cells represented the same Th1 phenotype as that of monospecific T cells recognizing MBP(93-105). There were increased antibody titers for both peptide HHV-6 (U24)(1-13) and peptide MBP(93-105) in the same patients with MS compared with those in healthy controls, suggesting B-cell sensitization to the antigens in MS patients. The study provides important evidence in the understanding of the potential role of HHV-6 infection/reactivation in the activation of autoimmune reactivity to MBP and its implication in the pathogenesis of MS.

Human herpesvirus 6 and Chlamydia pneumoniae as etiologic agents in multiple sclerosis - a critical review

Multiple sclerosis (MS) is thought by many investigators to have an infectious component, and several microorganisms have been associated with the disease during the last three decades. Recent studies have implicated both human herpesvirus 6 (HHV-6) and the obligate intracellular bacterium Chlamydia pneumoniae in the etiology of MS. As with earlier studies of other potential agents, however, evidence linking either of these organisms to the disease is equivocal. In this article, we review data for and against involvement of HHV-6 and C. pneumoniae in MS, as well as evidence concerning auxiliary factors, such as possession of the APOE epsilon4 allele, which may influence the role of these organisms in pathogenesis. Further, we suggest several lines of investigation that should clarify whether either or both pathogens are associated meaningfully with this disease.

Identification and characterization of the gene products of open reading frame U86/87 of human herpesvirus 6

The human herpesvirus 6 (HHV-6) immediate early-A locus (IE-A) locates in the position analogous to the human cytomegalovirus (HCMV) major IE (MIE) locus that is well-known to play critical roles in viral infection. Similarly to HCMV MIE, HHV-6 IE-A consists of two genetic units, IE1 and IE2, corresponding to open reading frames U90-U89 and U90-U86/87, respectively. However, the HHV-6 IE-A locus exhibits limited sequence homology with the HCMV MIE locus. In this study, to characterize HHV-6 IE2 gene products, polyclonal antibodies against four domains of the U86/87 open reading frame were generated by immunization of rabbits with bacterially-expressed proteins. Three polypeptides derived from the U86/87 region with apparent molecular masses of 100, 85 and 55 kD were detected in HHV-6-infected cells 3 days after infection, while IE1 polypeptides with apparent molecular mass greater than 170 kD were detectable as early as 8 h. Mapping of the IE2 gene products with the antibodies suggests differential splicing and alternative translation initiation in the IE2 genetic unit. The IE2 products show a mixed cytoplasmic and nuclear localization pattern. In addition, the 437 amino acid carboxyl-terminus domain bound to a DNA fragment containing the putative IE-A promoter. These results suggest that HHV-6 IE2 plays a critical role in transcriptional regulation and viral growth as does HCMV IE2, although it is likely that HHV-6 IE2 has expression kinetics different from HCMV IE2.