Increased lymphoproliferative response to human herpesvirus type 6A variant in multiple sclerosis patients

Human herpesvirus 6A and axonal injury before the clinical onset of multiple sclerosis

Recent research indicates that multiple sclerosis is preceded by a prodromal phase with elevated levels of serum neurofilament light chain (sNfL), a marker of axonal injury. The effect of environmental risk factors on the extent of axonal injury during this prodrome is unknown. Human herpesvirus 6A (HHV-6A) is associated with an increased risk of developing multiple sclerosis. The objective of this study was to determine if HHV-6A serostatus is associated with the level of sNfL in the multiple sclerosis prodrome, which would support a causative role of HHV-6A. A nested case-control study was performed by crosslinking multiple sclerosis registries with Swedish biobanks. Individuals with biobank samples collected before the clinical onset of multiple sclerosis were included as cases. Controls without multiple sclerosis were randomly selected, matched for biobank, sex, sampling date and age. Serostatus of HHV-6A and Epstein-Barr virus was analysed with a bead-based multiplex assay. The concentration of sNfL was analysed with single molecule array technology. The association between HHV-6A serology and sNfL was assessed by stratified t-tests and linear regressions, adjusted for Epstein-Barr virus serostatus and sampling age. Within-pair ratios of HHV-6A seroreactivity and sNfL were calculated for each case and its matched control. To assess the temporal relationship between HHV-6A antibodies and sNfL, these ratios were plotted against the time to the clinical onset of multiple sclerosis and compared using locally estimated scatterplot smoothing regressions with 95% confidence intervals (CI). Samples from 519 matched case-control pairs were included. In cases, seropositivity of HHV-6A was significantly associated with the level of sNfL (+11%, 95% CI 0.2-24%, P = 0.045) and most pronounced in the younger half of the cases (+24%, 95% CI 6-45%, P = 0.007). No such associations were observed among the controls. Increasing seroreactivity against HHV-6A was detectable before the rise of sNfL (significant within-pair ratios from 13.6 years versus 6.6 years before the clinical onset of multiple sclerosis). In this study, we describe the association between HHV-6A antibodies and the degree of axonal injury in the multiple sclerosis prodrome. The findings indicate that elevated HHV-6A antibodies both precede and are associated with a higher degree of axonal injury, supporting the hypothesis that HHV-6A infection may contribute to multiple sclerosis development in a proportion of cases.

The Role of Microorganisms in the Etiopathogenesis of Demyelinating Diseases

Multiple sclerosis (MS), neuromyelitis optica (NMO) and myelin oligodendrocyte glycoprotein antibody disease (MOGAD) are inflammatory diseases of the central nervous system (CNS) with a multifactorial aetiology. Environmental factors are important for their development and microorganisms could play a determining role. They can directly damage the CNS, but their interaction with the immune system is even more important. The possible mechanisms involved include molecular mimicry, epitope spreading, bystander activation and the dual cell receptor theory. The role of Epstein-Barr virus (EBV) in MS has been definitely established, since being seropositive is a necessary condition for the onset of MS. EBV interacts with genetic and environmental factors, such as low levels of vitamin D and human endogenous retrovirus (HERV), another microorganism implicated in the disease. Many cases of onset or exacerbation of neuromyelitis optica spectrum disorder (NMOSD) have been described after infection with Mycobacterium tuberculosis, EBV and human immunodeficiency virus; however, no definite association with a virus has been found. A possible role has been suggested for Helicobacter pylori, in particular in individuals with aquaporin 4 antibodies. The onset of MOGAD could occur after an infection, mainly in the monophasic course of the disease. A role for the HERV in MOGAD has been hypothesized. In this review, we examined the current understanding of the involvement of infectious factors in MS, NMO and MOGAD. Our objective was to elucidate the roles of each microorganism in initiating the diseases and influencing their clinical progression. We aimed to discuss both the infectious factors that have a well-established role and those that have yielded conflicting results across various studies.

Role of Microglia in Herpesvirus-Related Neuroinflammation and Neurodegeneration

Neuroinflammation is defined as an inflammatory state within the central nervous system (CNS). Microglia conprise the resident tissue macrophages of the neuronal tissue. Upon viral infection of the CNS, microglia become activated and start to produce inflammatory mediators important for clearance of the virus, but an excessive neuroinflammation can harm nearby neuronal cells. Herpesviruses express several molecular mechanisms, which can modulate apoptosis of infected neurons, astrocytes and microglia but also divert immune response initiated by the infected cells. In this review we also describe the link between virus-related neuroinflammation, and development of neurodegenerative diseases.

Human Herpesvirus 6A Is a Risk Factor for Multiple Sclerosis

The role for human herpesvirus (HHV)-6A or HHV-6B in multiple sclerosis (MS) pathogenesis has been controversial. Possibly because the damage of the virus infection may occur before onset of clinical symptoms and because it has been difficult to detect active infection and separate serological responses to HHV-6A or 6B. Recent studies report that in MS patients the serological response against HHV-6A is increased whereas it is decreased against HHV-6B. This effect seems to be even more pronounced in MS patients prior to diagnosis and supports previous studies postulating a predomination for HHV-6A in MS disease and suggests that the infection is important at early stages of the disease. Furthermore, HHV-6A infection interacts with other factors suspected of modulating MS susceptibility and progression such as infection with Epstein-Barr virus (EBV) and Cytomegalovirus (CMV), tobacco smoking, HLA alleles, UV irradiation and vitamin D levels. The multifactorial nature of MS and pathophysiological role for HHV-6A in inflammation and autoimmunity are discussed.

Cumulative Roles for Epstein-Barr Virus, Human Endogenous Retroviruses, and Human Herpes Virus-6 in Driving an Inflammatory Cascade Underlying MS Pathogenesis

Roles for viral infections and aberrant immune responses in driving localized neuroinflammation and neurodegeneration in multiple sclerosis (MS) are the focus of intense research. Epstein-Barr virus (EBV), as a persistent and frequently reactivating virus with major immunogenic influences and a near 100% epidemiological association with MS, is considered to play a leading role in MS pathogenesis, triggering localized inflammation near or within the central nervous system (CNS). This triggering may occur directly via viral products (RNA and protein) and/or indirectly via antigenic mimicry involving B-cells, T-cells and cytokine-activated astrocytes and microglia cells damaging the myelin sheath of neurons. The genetic MS-risk factor HLA-DR2b (DRB1*1501β, DRA1*0101α) may contribute to aberrant EBV antigen-presentation and anti-EBV reactivity but also to mimicry-induced autoimmune responses characteristic of MS. A central role is proposed for inflammatory EBER1, EBV-miRNA and LMP1 containing exosomes secreted by viable reactivating EBV+ B-cells and repetitive release of EBNA1-DNA complexes from apoptotic EBV+ B-cells, forming reactive immune complexes with EBNA1-IgG and complement. This may be accompanied by cytokine- or EBV-induced expression of human endogenous retrovirus-W/-K (HERV-W/-K) elements and possibly by activation of human herpesvirus-6A (HHV-6A) in early-stage CNS lesions, each contributing to an inflammatory cascade causing the relapsing-remitting neuro-inflammatory and/or progressive features characteristic of MS. Elimination of EBV-carrying B-cells by antibody- and EBV-specific T-cell therapy may hold the promise of reducing EBV activity in the CNS, thereby limiting CNS inflammation, MS symptoms and possibly reversing disease. Other approaches targeting HHV-6 and HERV-W and limiting inflammatory kinase-signaling to treat MS are also being tested with promising results. This article presents an overview of the evidence that EBV, HHV-6, and HERV-W may have a pathogenic role in initiating and promoting MS and possible approaches to mitigate development of the disease.

Cytomegalovirus seropositivity is associated with reduced risk of multiple sclerosis-a presymptomatic case-control study

BACKGROUND AND PURPOSE

Epstein-Barr virus (EBV) and human herpesvirus 6A (HHV-6A) are associated with increased risk of multiple sclerosis (MS). Conversely, infection with cytomegalovirus (CMV) has been suggested to reduce the risk of MS but supporting data from presymptomatic studies are lacking. Here, it was sought to increase the understanding of CMV in MS aetiology.

METHODS

A nested case-control study was performed with presymptomatically collected blood samples identified through crosslinkage of MS registries and Swedish biobanks. Serological antibody response against CMV, EBV and HHV-6A was determined using a bead-based multiplex assay. Odds ratio (OR) with 95% confidence interval (CI) for CMV seropositivity as a risk factor for MS was calculated by conditional logistic regression and adjusted for EBV and HHV-6A seropositivity. Potential interactions on the additive scale were analysed by calculating the attributable proportion due to interaction (AP).

RESULTS

Serum samples from 670 pairs of matched cases and controls were included. CMV seropositivity was associated with a reduced risk for MS (OR = 0.70, 95% CI 0.56-0.88, p = 0.003). Statistical interactions on the additive scale were observed between seronegativity for CMV and seropositivity against HHV-6A (AP 0.34, 95% CI 0.06-0.61) and EBV antigen EBNA-1 (amino acid 385-420) at age 20-39 years (AP 0.37, 95% CI 0.09-0.65).

CONCLUSIONS

Cytomegalovirus seropositivity is associated with a decreased risk for MS. The protective role for CMV infection in MS aetiology is further supported by the interactions between CMV seronegativity and EBV and HHV-6A seropositivity.

The Combination of gQ1 and gQ2 in Human Herpesvirus 6A and 6B Regulates the Viral Tetramer Function for Their Receptor Recognition

Human herpesvirus 6A (HHV-6A) and HHV-6B use different cellular receptors, human CD46 and CD134, respectively and have different cell tropisms although they have 90% similarity at the nucleotide level. An important feature that characterizes HHV-6A/6B is the glycoprotein H (gH)/gL/gQ1/gQ2 complex (a tetramer) that each virus has specifically on its envelope. Here, to determine which molecules in the tetramer contribute to the specificity for each receptor, we developed a cell-cell fusion assay system for HHV-6A and HHV-6B that uses the cells expressing CD46 or CD134. With this system, when we replaced the gQ1 or gQ2 of HHV-6A with that of HHV-6B in the tetramer, the cell fusion activity mediated by glycoproteins via CD46 was lower than that done with the original-type tetramer. When we replaced the gQ1 or the gQ2 of HHV-6A with that of HHV-6B in the tetramer, the cell fusion mediated by glycoproteins via CD134 was not seen. In addition, we generated two types of C-terminal truncation mutants of HHV-6A gQ2 (AgQ2) to examine the interaction domains of HHV-6A gQ1 (AgQ1) and AgQ2. We found that amino acid residues 163 to 185 in AgQ2 are important for interaction of AgQ1 and AgQ2. Finally, to investigate whether HHV-6B gQ2 (BgQ2) can complement AgQ2, an HHV-6A genome harboring BgQ2 was constructed. The mutant could not produce an infectious virus, indicating that BgQ2 cannot work for the propagation of HHV-6A. These results suggest that gQ2 supports the tetramer's function, and the combination of gQ1 and gQ2 is critical for virus propagation.IMPORTANCE Glycoprotein Q2 (gQ2), an essential gene for virus propagation, forms a heterodimer with gQ1. The gQ1/gQ2 complex has a critical role in receptor recognition in the gH/gL/gQ1/gQ2 complex (a tetramer). We investigated whether gQ2 regulates the specific interaction between the HHV-6A or -6B tetramer and CD46 or CD134. We established a cell-cell fusion assay system for HHV-6A/6B and switched the gQ1 or gQ2 of HHV-6A with that of HHV-6B in the tetramer. Although cell fusion was induced via CD46 when gQ1 or gQ2 was switched between HHV-6A and -6B, the activity was lower than that of the original combination. When gQ1 or gQ2 was switched in HHV-6A and -6B, no cell fusion was observed via CD134. HHV-6B gQ2 could not complement the function of HHV-6A's gQ2 in HHV-6A propagation, suggesting that the combination of gQ1 and gQ2 is critical to regulate the specificity of the tetramer's function for virus entry.

Human Herpesvirus 6A Induces Dendritic Cell Death and HMGB1 Release without Virus Replication

Human herpesvirus 6A (HHV-6A) is a common virus that has important immunomodulatory effects. Dendritic cells (DC) are key players in innate and adaptive immunity and are implicated in the pathogenesis of many human diseases, including infections. (1) Background: Previous studies have demonstrated suppressive effects of HHV-6A on key DC functions. (2) Methods: human monocyte derived dendritic cells were inoculated with HHV-6A and viral replication, cell viability, and release of high mobility group box 1 (HMGB1) protein from DC and of the cytokines IL-2, IL-4, IL-6, IL-10, TNF and IFN-γ after co-culture with allogenic CD4+ T cells were assessed. (3) Results: Nonproductive infection of HHV-6A in DC leads to titer-dependent cell death and the release of HMGB1 protein, and a Th2 polarization. (4) Conclusion: These immune responses aimed to clear the infection may also imply risks for inflammatory pathologies associated with HHV-6A such as multiple sclerosis.

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.

The Presence of Human Herpesvirus 6 in the Brain in Health and Disease

The human herpesvirus 6 (HHV-6) -A and -B are two dsDNA beta-herpesviruses infectingalmost the entire worldwide population. These viruses have been implicated in multipleneurological conditions in individuals of various ages and immunological status, includingencephalitis, epilepsy, and febrile seizures. HHV-6s have also been suggested as playing a role inthe etiology of neurodegenerative diseases such as multiple sclerosis and Alzheimer's disease. Theapparent robustness of these suggested associations is contingent on the accuracy of HHV-6detection in the nervous system. The effort of more than three decades of researching HHV-6 in thebrain has yielded numerous observations, albeit using variable technical approaches in terms oftissue preservation, detection techniques, sample sizes, brain regions, and comorbidities. In thisreview, we aimed to summarize current knowledge about the entry routes and direct presence ofHHV-6 in the brain parenchyma at the level of DNA, RNA, proteins, and specific cell types, inhealthy subjects and in those with neurological conditions. We also discuss recent findings relatedto the presence of HHV-6 in the brains of patients with Alzheimer's disease in light of availableevidence.

The role of herpesvirus 6A and 6B in multiple sclerosis and epilepsy

Human herpesvirus 6A (HHV‐6A) and 6B (HHV‐6B) are two closely related viruses that can infect cells of the central nervous system (CNS). The similarities between these viruses have made it difficult to separate them on serological level. The broad term HHV‐6 remains when referring to studies where the two species were not distinguished, and as such, the seroprevalence is over 90% in the adult population. HHV‐6B has been detected in up to 100% of infants with the primary infection roseola infantum, but less is known about the primary infection of HHV‐6A. Both viruses are neurotropic and have capacity to establish lifelong latency in cells of the central nervous system, with potential to reactivate and cause complications later in life. HHV‐6A infection has been associated with an increased risk of multiple sclerosis (MS), whereas HHV‐6B is indicated to be involved in pathogenesis of epilepsy. These two associations show how neurological diseases might be caused by viral infections, but as suggested here, through completely different molecular mechanisms, in an autoimmune disease, such as MS, by triggering an overreaction of the immune system and in epilepsy by hampering internal cellular functions when the immune system fails to eliminate the virus. Understanding the viral mechanisms of primary infection and reactivation and their spectrum of associated symptoms will aid our ability to diagnose, treat and prevent these severe and chronic diseases. This review explores the role of HHV‐6A and HHV‐6B specifically in MS and epilepsy, the evidence to date and the future directions of this field.

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.

Anti-human herpesvirus 6A/B IgG correlates with relapses and progression in multiple sclerosis

OBJECTIVE

To analyze the titers of the IgG and IgM antibodies against human herpesvirus 6A/B (HHV-6A/B) in multiple sclerosis (MS) patients treated with different disease modified therapies (DMTs) along two-years of follow-up.

METHODS

We collected 2163 serum samples from 596 MS; for 301 MS patients a 2-years follow-up was performed. Serum samples of 337 healthy controls were also analyzed. Anti-HHV-6A/B IgG and IgM were analyzed by ELISA (Panbio).

RESULTS

We found that 129/187 (69.0%) MS patients with a decrease of the anti-HHV-6A/B IgG titers after 2-years with DMTs were free of relapses and progression vs. 46/113 (40.7%) of MS patients with an increase of the anti-HHV-6A/B IgG titers (p = 0.0000015); the higher significance was found for natalizumab. Furthermore, we found that anti-HHV-6A/B IgG titers reached their highest value two weeks before the relapse (p = 0.0142), while the anti-HHV-6A/B IgM titers reached their highest value one month before the relapse (p = 0.0344).

CONCLUSION

The measurement of the anti-HHV-6A/B IgG titers could be a good biomarker of clinical response to the different DMTs. The increase of the anti-HHV-6A/B IgG and IgM titers predicts the upcoming clinical relapses. However, further longitudinal studies are needed to validate these results.

Coinfection of human herpesviruses 6A (HHV-6A) and HHV-6B as demonstrated by novel digital droplet PCR assay

The human herpesviruses HHV-6A and HHV-6B have been associated with various neurologic disorders partly due to the detection of elevated viral DNA levels in patients compared to controls. However the reported frequency of these viruses varies widely, likely reflecting differences in PCR methodologies used for detection. Digital droplet PCR (ddPCR) is a third generation PCR technology that enables the absolute quantification of target DNA molecules. Mounting evidence of the biological differences between HHV-6A and HHV-6B has led to their recent reclassification as separate species. As it is now especially relevant to investigate each virus, our objectives were to first design a multiplex HHV-6A and HHV-6B ddPCR assay and then to investigate the incidence of HHV-6A and HHV-6B coinfection in samples from healthy donors and patients with MS, a disease in which HHV-6 is thought to play a role. In our assessment of healthy donors, we observed a heretofore-underappreciated high frequency of coinfection in PBMC and serum, and found that our assay precisely detects both HHV-6A and HHV-6B chromosomally integrated virus, which has important implications in clinical settings. Interestingly, upon comparing the saliva from MS patients and healthy donors, we detected a significantly elevated frequency of coinfection in MS saliva; increased detection of HHV-6A in MS patients is consistent with other studies suggesting that this viral species (thought to be more neurotropic than HHV-6B) is more prevalent among MS patients compared to healthy donors. As the biology and disease associations between these two viral species differ, identifying and quantifying both species of HHV-6 may provide clinically relevant information, as well as enhance our understanding of the roles of each in health and disease.

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 neurodegeneration

Neurodegenerative diseases (NDs) are chronic degenerative diseases of the central nervous system (CNS), which affect 37 million people worldwide. As the lifespan increases, the NDs are the fourth leading cause of death in the developed countries and becoming increasingly prevalent in developing countries. Despite considerable research, the underlying mechanisms remain poorly understood. Although the large majority of studies do not show support for the involvement of pathogenic aetiology in classical NDs, a number of emerging studies show support for possible association of viruses with classical neurodegenerative diseases in humans. Space does not permit for extensive details to be discussed here on non-viral-induced neurodegenerative diseases in humans, as they are well described in literature.Viruses induce alterations and degenerations of neurons both directly and indirectly. Their ability to attack the host immune system, regions of nervous tissue implies that they can interfere with the same pathways involved in classical NDs in humans. Supporting this, many similarities between classical NDs and virus-mediated neurodegeneration (non-classical) have been shown at the anatomic, sub-cellular, genomic and proteomic levels suggesting that viruses can explain neurodegenerative disorders mechanistically. The main objective of this review is to provide readers a detailed snapshot of similarities viral and non-viral neurodegenerative diseases share, so that mechanistic pathways of neurodegeneration in human NDs can be clearly understood. Viruses can guide us to unveil these pathways in human NDs. This will further stimulate the birth of new concepts in the biological research, which is needed for gaining deeper insights into the treatment of human NDs and delineate mechanisms underlying neurodegeneration.

Human Herpesvirus 6 and Neuroinflammation

Human herpesvirus (HHV-) 6A and HHV-6B are two distinct β-herpesviruses which have been associated with various neurological diseases, including encephalitis, meningitis, epilepsy, and multiple sclerosis. Although the reactivation of both viruses is recognized as the cause of some neurological complications in conditions of immunosuppression, their involvement in neuroinflammatory diseases in immunocompetent people is still unclear, and the mechanisms involved have not been completely elucidated. Here, we review the available data providing evidence for the capacity of HHV-6A and -6B to infect the central nervous system and to induce proinflammatory responses by infected cells. We discuss the potential role of both viruses in neuroinflammatory pathologies and the mechanisms which could explain virus-induced neuropathogenesis.

Calibrated real-time polymerase chain reaction for specific quantitation of HHV-6A and HHV-6B in clinical samples

The recent classification of human herpesvirus 6 (HHV-6) A and B, previously considered as two variants of the same virus, as two distinct herpesvirus species, emphasizes the need to develop and standardize specific methods for their detection and quantitation for clinical use. The development of two highly sensitive calibrated real-time PCR to quantify HHV-6A and -6B variants in clinical specimen is described. Both assays displayed the same wide linear dynamic range from 10(0) to 10(6) copies of viral DNA in a single reaction and sensitivity of one copy/reaction. These systems allow for HHV-6A/B DNA load quantitation in different types of clinical specimens: blood or tissue cells when combined with the CCR5 assay; cell-free samples (plasma or other biological fluids) in combination with the calibrator technology. Due to the absence of cross-amplification and cross-hybridization, these methods detect minute amounts of one viral species even in the presence of a large excess of the other, allowing a specific quantitation of both viruses in the case of mixed infections. The new qPCR methods provide sensitive and specific tool for monitoring HHV-6A/B DNA load in clinical samples, facilitating the study of these viruses in human diseases.

Novel marmoset (Callithrix jacchus) model of human Herpesvirus 6A and 6B infections: immunologic, virologic and radiologic characterization

Human Herpesvirus 6 (HHV-6) is a ubiquitous virus with an estimated seroprevalence of 95% in the adult population. HHV-6 is associated with several neurologic disorders, including multiple sclerosis, an inflammatory demyelinating disease affecting the CNS. Animal models of HHV-6 infection would help clarify its role in human disease but have been slow to develop because rodents lack CD46, the receptor for cellular entry. Therefore, we investigated the effects of HHV-6 infections in a non-human primate, the common marmoset Callithrix jacchus. We inoculated a total of 12 marmosets with HHV-6A and HHV-6B intravenously and HHV-6A intranasally. Animals were monitored for 25 weeks post-inoculation clinically, immunologically and by MRI. Marmosets inoculated with HHV-6A intravenously exhibited neurologic symptoms and generated virus-specific antibody responses, while those inoculated intravenously with HHV-6B were asymptomatic and generated comparatively lower antibody responses. Viral DNA was detected at a low frequency in paraffin-embedded CNS tissue of a subset of marmosets inoculated with HHV-6A and HHV-6B intravenously. When different routes of HHV-6A inoculation were compared, intravenous inoculation resulted in virus-specific antibody responses and infrequent detection of viral DNA in the periphery, while intranasal inoculation resulted in negligible virus-specific antibody responses and frequent detection of viral DNA in the periphery. Moreover, marmosets inoculated with HHV-6A intravenously exhibited neurologic symptoms, while marmosets inoculated with HHV-6A intranasally were asymptomatic. We demonstrate that a marmoset model of HHV-6 infection can serve to further define the contribution of this ubiquitous virus to human neurologic disorders.

Monitoring of active human herpes virus 6 infection in Iranian patients with different subtypes of multiple sclerosis

Background. Recently, it has been suggested that human herpes virus 6 (HHV6) may play a role in the pathogenesis of multiple sclerosis (MS). Our purpose is to determine the incidence of reactivated HHV6 in MS patients. Methods. Viral sequence analyzed by qPCR in the peripheral blood mononuclear cells (PBMCs), serum, and saliva samples of different subtypes of MS patients (n = 78) and healthy controls (n = 123). HHV6 IgG and IgM antibody levels measured by ELISA technique in the plasma samples of both groups. Likewise, cerebrospinal fluid (CSF) samples of some MS patients (n = 38) were analyzed for viral sequence. Results. Results demonstrate increased levels of anti-HHV6-IgG (78.2% versus 76.4% in controls; P = NS), and IgM (34.6% versus 6.5% in controls; P < 0.05) in MS patients. Furthermore, RRMS and SPMS patients showed relatively higher anti-HHV6 IgG and IgM compared to PPMS (P < 0.001). Moreover, load of cell-free viral DNA was higher in RRMS and SPMS patients and detected in 60.2% (47/78) of MS patients, compared with 14.6% (18/123) of healthy controls (P < 0.001). Moreover, load of cell-free viral DNA was higher in RRMS and SPMS patients and detected in 60.2% (47/78) of MS patients, compared with 14.6% (18/123) of healthy controls (P < 0.001). Conclusions. The results extend the observation of an increased frequency of systemic reactivated HHV6 infection in MS patients with developed stages of disease.

Insight into the role of CRMP2 (collapsin response mediator protein 2) in T lymphocyte migration: the particular context of virus infection

Lymphocyte migration into the central nervous system is a critical step in the physiopathology of a variety of neurological diseases, including multiple sclerosis and virus-induced neuroinflammation. To better understand the molecular mechanisms involved in cells migration, we focused our studies on collapsin response mediator proteins (CRMPs), a group of phosphoproteins that mediate neural cell motility. There is now evidence that collapsin response mediator protein 2 (CRMP2) plays critical roles in the polarization (uropod formation) of T lymphocytes and their subsequent migration. CRMP2 was known to respond to semaphorin, ephrin and neurotrophin signaling in neurons. The link between the chemokine CXCL12, CRMP2 activity and cell migration has been demonstrated in T lymphocytes. These observations and comparisons of the activity of CRMPs in immune and non-immmune cells are summarized here. The ability of a human retrovirus to enhance lymphocyte migration through the modulation of CRMP2 activity is also discussed. In conclusion, viruses have the ability to manipulate the lymphocyte motility machinery, intensifying neural tissue invasion in infected patients.

Identification of human herpesviruses 1 to 8 in Tunisian multiple sclerosis patients and healthy blood donors

Members of the human Herpesviridae family are candidates for representing the macroenvironmental factors associated with multiple sclerosis (MS) pathogenesis. To verify the possible role of human herpesviruses (HHVs) as triggering or aggravating factors in relapsing-remitting multiple sclerosis clinical outcome, we studied the prevalence of all eight human herpesviruses in whole blood samples collected from 51 MS patients and from 51 healthy controls. The presence of DNA of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2), varicella zoster virus (VZV), Epstein-Barr virus (EBV), human cytomegalovirus (HCMV), human herpesvirus 6 (HHV-6), human herpesvirus 7 (HHV-7) and human herpesvirus 8 (HHV-8) was searched by specific nested polymerase chain reaction. HHVs were significantly more prevalent in the blood of MS patients than in those of the controls (P < 10(-4)). HSV-1, HSV-2, HCMV and HHV-8 were negative in both MS patients and controls samples. In MS patients, EBV, HHV-7, HHV-6 and VZV were detected in 31.3%, 33.3%, 5.8% and 7.8% of samples, respectively, compared with 3.9%, 9.8%, 1.96% and 1.96%, respectively, of samples from controls. We found a statistically significant difference only for EBV DNA and for HHV-7 DNA prevalence (P < 0.001 and P = 0.03). Although these results indicate lack of apparent association in terms of gender, type of diagnosis, symptoms, disease score and β interferon treatment between EBV or HHV-7 to MS among Tunisian patients, heterogeneity related to genetic polymorphism as well as geographical distribution of the disease and of pathogens may be of significance.

The molecular biology of human herpesvirus-6 latency and telomere integration

The genomes of herpesviruses establish latency as a circular episome. However, Human herpesvirus-6 (HHV-6) has been shown to specifically integrate into the telomeres of chromosomes during latency and vertically transmit through the germ-line. This review will focus on the telomere integration of HHV-6, the potential viral and cellular genes that mediate integration, and the clinical impact on the host.

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.

Mechanism of neuroinflammation: enhanced cytotoxicity and IL-17 production via CD46 binding

The membrane co-factor protein CD46 is the cellular receptor for a number of pathogens including the human herpesvirus 6 (HHV-6). In addition to its function as an inhibitory complement receptor, engagement of CD46 in the context of T-cell receptor (TCR) signaling influences T-cell activation. Simultaneous cross-linking of the CD3/CD46 molecules led to differentiation of a unique population of CD4+ T-cell subset characterized by enhanced expressions of IFN-gamma, IL-10, granzyme B, adhesion molecule MAdCAM-1 (alpha-4-beta-7), surface-bound cytokine LIGHT, and chemokine receptor CCR9. Multiple sclerosis is a chronic inflammatory neurodegenerative disorder of the central nervous system (CNS) with unknown etiology. The HHV-6 is a candidate pathogen in MS and uses the CD46 molecule as its receptor. We hypothesize that binding of the HHV-6 glycoprotein to CD46 may trigger a pro-inflammatory response that could contribute to CNS tissue damage. To address this question, we examined immunological parameters such as proliferation, cytokine production and cytotoxic functions in CD4+ T cells of healthy individuals and MS patients following CD3/CD46 co-engagement by using anti-CD3 and anti-CD46 monoclonal antibodies as surrogates to mimic T-cell receptor and CD46 signaling. Our results demonstrated that CD3/CD46 cross-linking induced expression of IL-1beta and IL-17A in multiple sclerosis patient T cells. Additionally, increase in transient surface expression of lysosomal associated protein CD107a suggested enhanced CD4+ T-cell cytotoxic functions following CD3/CD46 co-stimulation. Collectively, this study demonstrated evidence to suggest a potential mechanism of virus-induced neuroinflammation that may be involved in MS disease pathogenesis.

A mechanism of virus-induced demyelination

Myelin forms an insulating sheath surrounding axons in the central and peripheral nervous systems and is essential for rapid propagation of neuronal action potentials. Demyelination is an acquired disorder in which normally formed myelin degenerates, exposing axons to the extracellular environment. The result is dysfunction of normal neuron-to-neuron communication and in many cases, varying degrees of axonal degeneration. Numerous central nervous system demyelinating disorders exist, including multiple sclerosis. Although demyelination is the major manifestation of most of the demyelinating diseases, recent studies have clearly documented concomitant axonal loss to varying degrees resulting in long-term disability. Axonal injury may occur secondary to myelin damage (outside-in model) or myelin damage may occur secondary to axonal injury (inside-out model). Viral induced demyelination models, has provided unique imminent into the cellular mechanisms of myelin destruction. They illustrate mechanisms of viral persistence, including latent infections, virus reactivation and viral-induced tissue damage. These studies have also provided excellent paradigms to study the interactions between the immune system and the central nervous system (CNS). In this review we will discuss potential cellular and molecular mechanism of central nervous system axonal loss and demyelination in a viral induced mouse model of multiple sclerosis.

HHV-6 infection in multiple sclerosis. A clinical and laboratory analysis

BACKGROUND AND PURPOSE

To elucidate the role of human herpesvirus-6 (HHV-6) in the development of multiple sclerosis (MS).

PATIENTS AND METHODS

Nine patients with MS and with acute or chronic HHV-6 infection were evaluated.

RESULTS

Intrathecal antibody production to HHV-6 and oligoclonal IgG bands in the cerebrospinal fluid (CSF) was observed in two patients with a clinically definite MS and chronic HHV-6 infection (based on the presence of HHV-6 specific antibodies in the CSF). A temporal association between the symptoms of clinically possible MS and acute primary HHV-6A infection (based on avidity of HHV-6 specific antibodies) was observed in two patients.

CONCLUSIONS

Human herpesvirus-6 infection may be an associated agent in some MS cases. Viral studies are needed to identify a possible viral etiology and give specific therapy.

HHV-6A infection induces expression of HERV-K18-encoded superantigen

BACKGROUND

The human endogenous retrovirus K-18 (HERV-K18) encodes a superantigen that causes deregulation of the immune system. This provirus is transcriptionally silent, but can be induced by Epstein-Barr virus (EBV) infection and IFN-alpha treatment.

OBJECTIVES

Since the herpesvirus EBV induces HERV-K18 expression in human B cells, it was of interest to determine if other herpesviruses would have similar HERV-K18 transactivation properties. Human herpesvirus (HHV)-6A, a neurotropic virus associated with multiple sclerosis, was a logical candidate for these studies.

STUDY DESIGN

HSB2 cells (HHV-6-negative control), HSB2-ML cells (containing latent HHV-6A genome) and HSB2/HHV-6A cells (HSB-2 cells productively infected with HHV-6A) were compared for their level of HERV-K18 transcription, using quantitative RT-PCR.

RESULTS

Latently infected HSB2-ML cells showed a significant increase in HERV-K18 RNA compared to the control cells. HERV-K18 expression was even greater in HSB2 cells productively infected with HHV-6A for 78h.

CONCLUSION

These results imply that HHV-6A, either in latent form or during acute infection, directly transactivates HERV-K18. This HERV-K18 induction may be mediated through IFN-alpha that is produced by the HHV-6A-infected cells. The functional implications of superantigen expression are discussed.

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.

Reactivation of human herpesvirus-6 in natalizumab treated multiple sclerosis patients

The alpha(4) integrin antagonist natalizumab was shown to be effective in patients with immune-mediated disorders but was unexpectedly associated with JC polyomavirus associated progressive multifocal leukoencephalopathy (PML) in two multiple sclerosis (MS) and one Crohn's disease patients. Impaired immune surveillance due to natalizumab treatment may have contributed to the JCV reactivation. As HHV-6 has been suggested to play a role in MS, we asked whether this virus could also have been reactivated during natalizumab therapy. Matched sera and CSF from a limited set of MS patients treated with and without natalizumab were examined for evidence of HHV-6. In addition, we also superinfected a persistent JC virus infected glial cell with HHV-6A to determine if JC virus can be increased. Elevated serum HHV6 IgG and HHV-6A DNA was detected in the CSF of a subset of patients but not controls. We confirmed that superinfection with HHV-6 of a JC virus infected glial cells increased expression of JCV. These results support the hypothesis that treatment with natalizumab may be associated with reduced immune surveillance resulting in reactivation of viruses associated with MS pathogenesis.

Infection of murine oligodendroglial precursor cells with Human Herpesvirus 6 (HHV-6)--establishment of a murine in vitro model

BACKGROUND

Human Herpesvirus 6 was previously demonstrated to infect human oligodendroglial precursor cells (OPCs) in vitro causing cell cycle arrest and premature differentiation with consequent loss of the precursor pool.

OBJECTIVES

To develop an in vitro murine OPC model to study the cell cycle and differentiation effects of HHV-6 in more readily available, genetically well-defined cells free of the risk of contamination with human herpesviruses.

STUDY DESIGN

Murine OPCs were exposed to infectious HHV-6A or HHV-6B and analyzed for production of viral transcripts, particles, and replicating virus. FACS analysis and specific markers were used to evaluate effects on cell cycling and differentiation.

RESULTS

HHV-6 infection of murine OPCs resulted in production of both immediate-early and some late transcripts but no replicating virus by TaqMan quantitative PCR or electron microscopy. Both a specific G1/S cell cycle arrest and premature loss of OPCs through differentiation into oligodendrocytes as previously seen with human precursors were recapitulated.

CONCLUSIONS

Infection of murine OPCs by HHV-6 reproduces the critical phenotypes of cell cycle arrest and altered differentiation seen in human cells. The murine system provides a highly defined, accessible, and reproducible source of cells permitting the elucidation of specific viral and cell cycle genes involved in CNS viral infections of OPCs.

Activation of endogenous retrovirus reverse transcriptase in multiple sclerosis patient lymphocytes by inactivated HSV-1, HHV-6 and VZV

Human endogenous retroviruses (HERVs) and herpesviruses have been associated with the development of multiple sclerosis (MS). These virus groups interact with each other and have been shown to induce synergistic immune responses. Here, we focus on the possible role of herpesviruses as contributing factors in HERV activation. We demonstrate the ability of HSV-1, HHV-6, and VZV antigens to induce higher RT activity in peripheral lymphocytes from MS patients vs. controls during the first 6 days post-antigen stimulation. On subsequent days, only VZV can sustain the increase in the RT expression in cells from MS patients. The RT induction does not depend on herpes replication.

Clinical parameters and HHV-6 active replication in relapsing—remitting multiple sclerosis patients

BACKGROUND

Although the etiology of multiple sclerosis (MS) remains uncertain, clinical, epidemiological, and laboratory findings suggest that environmental factors may be involved in the disease.

OBJECTIVE

This study was undertaken in order to investigate the possible relation of human herpesvirus-6 (HHV-6) in relapsing-remitting MS (RRMS).

STUDY DESIGN

A one-year follow-up study was performed analyzing serum samples of 63 patients with RRMS and 63 healthy blood donors (HBD) by a quantitative real time PCR, to measure HHV-6 prevalence and viral load. Clinical data (starting age and EDSS increase) were collected.

RESULTS

(i) We found 25.4% of RRMS patients with at least one positive serum sample along the one year follow-up. (ii) 19.1% of RRMS samples in relapse had HHV-6 active infection vs. 7.9% of RRMS samples in remission. (iii) We only found variant A. (iv) RRMS patients with HHV-6 active replication initiated the disease 1.9 years earlier, and they had a higher EDSS increase.

CONCLUSIONS

A higher HHV-6A frequency of active infection seems to be related with the exacerbations in a subset of RRMS patients. Regarding the relationship between HHV-6A active infection and the clinical data in RRMS patients, further investigations are needed.

Sympathetic nervous system and neurotransmitters: their possible role in neuroimmunomodulation of multiple sclerosis and some other autoimmune diseases

Multiple sclerosis is still a disease without a cure. Although intensive research efforts have led to the development of drugs that modify the activity of the disease, most of them have various side effects and are expensive. At the same time it is becoming apparent that some remedies usually used to treat somatic and psychic disorders also have immunomodulating properties, and may help manage multiple sclerosis and other autoimmune diseases. We describe here the role of the sympathetic nervous system in the neuro-immune interaction in multiple sclerosis and other immune diseases with increased cellular immunity as well as neurochemical disturbances that take place in these disorders.

Differential HHV-6A gene expression in T cells and primary human astrocytes based on multi-virus array analysis

Human herpesvirus 6 (HHV-6) is a ubiquitous virus that has been associated with a wide spectrum of diseases, such as exanthem infantum, multiple sclerosis, seizures, encephalitis/meningitis, and more recently, mesial temporal lobe sclerosis. Although HHV-6 is known to predominately infect CD4+ T lymphocytes, its ability to infect neural glial cells has been demonstrated both in vitro and in vivo. Reactivation of latent HHV-6 infection in the brain has recently been suggested to play a role in the development of neuropathogenesis. To investigate the association of viral gene expression and disease pathogenesis, we developed a multi-virus array containing all open reading frames of the HHV-6 virus and other pathogenically related viruses (EBV, HBV, HHV-8, HIV-1, HTLV-1, HTLV-2) to study expression of viral gene transcripts. In this study, we infected CD4+ T lymphocytes and primary human astrocytes derived from brain biopsy material in vitro with the more neurotropic HHV-6A strain. Hierarchal cluster analysis based on gene expression over time suggested a temporally regulated herpesvirus transcription process. Furthermore, we compared viral gene expression in CD4+ T lymphocytes and primary human astrocytes at peak viral load levels (>10(8) copies of virus/10(6) cells) at 5 days post-infection. Differential expression of HHV-6A genes was observed between CD4+ T lymphocytes and primary human astrocytes. Absence of a number of HHV-6 genes detected at 5 days post-infection in primary human astrocytes suggests an alternative replication strategy used by HHV-6 to evade immune detection and allow establishment of persistent infection in neural glial cells.

Identification and Characterization of U83A Viral Chemokine, a Broad and Potent β-Chemokine Agonist for Human CCRs with Unique Selectivity and Inhibition by Spliced Isoform

Leukotropic human herpesvirus 6 (HHV-6) establishes a persistent infection associated with inflammatory diseases and encodes chemokines that could chemoattract leukocytes for infection or inflammation. HHV-6 variant A encodes a distant chemokine homolog, U83A, and a polymorphism promoting a secreted form was identified. U83A and three N-terminal modifications were expressed and purified, and activities were compared with a spliced truncated isoform, U83A-Npep. U83A efficiently and potently induced calcium mobilization in cells expressing single human CCR1, CCR4, CCR6, or CCR8, with EC50 values <10 nM. U83A also induced chemotaxis of Th2-like leukemic cells expressing CCR4 and CCR8. High-affinity binding, 0.4 nM, was demonstrated to CCR1 and CCR5 on monocytic/macrophage cells, and pretreatment with U83A or modified forms could block responses for endogenous ligands. U83A-Npep acted only as antagonist, efficiently blocking binding of CCL3 to CCR1 or CCR5 on differentiated monocytic/macrophage leukemic cells. Furthermore, CCL3 induction of calcium signaling via CCR1 and CCL1 induced chemotaxis via CCR8 in primary human leukocytes was inhibited. Thus, this blocking by the early expressed U83A-Npep could mediate immune evasion before finishing the replicative cycle. However, late in infection, when full-length U83A is made, chemoattraction of CCR1-, CCR4-, CCR5-, CCR6-, and CCR8-bearing monocytic/macrophage, dendritic, and T lymphocyte cells can facilitate dissemination via lytic and latent infection of these cells. This has further implications for neuroinflammatory diseases such as multiple sclerosis, where both cells bearing CCR1/CCR5 plus their ligands, as well as HHV-6A, have been linked. Applications also discussed include novel vaccines/immunotherapeutics for cancer and HIV as well as anti-inflammatories.

Differential tropism of human herpesvirus 6 (HHV-6) variants and induction of latency by HHV-6A in oligodendrocytes

Human herpesvirus 6 (HHV-6) is a ubiquitous β-herpesvirus associated with a number of clinical disorders. Two closely but biologically distinct variants have been described. HHV-6 variant B causes the common childhood disease exhanthem subitum, and although the pathologic characteristics for HHV-6 variant A are less well defined, HHV-6A has been suggested to be more neurotropic. We studied the effect of both HHV-6 variants in an oligodendrocyte cell line (MO3.13). Infection of M03.13 was monitored by cytopathic effect (CPE), quantitative TaqMan PCR for viral DNA in cells and supernatant, reverse transcriptase-polymerase chain reaction (RT-PCR) to detect viral RNA, and indirect immunofluorescence (IFA) to detect viral protein expression. HHV-6A infection induced significantly more CPE than infection with HHV-6B. HHV-6B induced an abortive infection associated with a decrease of the initial viral DNA load over time, early RNA expression, and no expression of viral antigen. In contrast, infection with HHV-6A DNA persisted in cells for at least 62 days. During the acute phase of infection with HHV-6A, intracellular and extracellular viral load increased and cells expressed the viral protein IE-2 and gp116/54/64. No HHV-6A RNA or protein was expressed after 30 days post infection, suggesting that HHV-6A formed a latent infection. These studies provide in vitro support to the hypothesis that HHV-6 can actively infect oligodendrocytes. Our results suggest that HHV-6A and HHV-6B have different tropism in MO3.13 cells and that an initially active HHV-6A infection can develop latency. Differences between HHV-6A and -6B infection in different neural cell types may be associated with different neurological diseases.

Post-mortem diagnosis of encephalitis in a 75-year-old man associated with human herpesvirus-6 variant A

An HHV-6 variant A infection is described in a 75 year-old man in association with meningoencephalitis identified at autopsy. The patient presented with fever and anorexia, then he developed altered consciousness, motor weakness, progressive lethargy, and coma, and died 21 days after hospital admission. Histopathological examination showed perivascular lymphocytic infiltrates in the central nervous system (CNS). Serum and cerebral spinal fluid (CSF) samples drawn from the patient were tested for viruses by a nested polymerase chain reaction (nPCR). HHV-6 primers A and C [Aubin et al., 1991: J Clin Microb 29: 367-372] and HS6AE and HS6AF from [Dewhurst et al. (1993): J Clin Microb 31: 416-418] disclosed a 750 bp genomic product of HHV-6 in both types of biological samples. Restricted site analysis showed that the HHV-6 DNA amplified belonged to the variant A of the virus. Short sequences of HHV-6 DNA could also be detected in the DNA extracted from formalin-fixed, paraffin-embedded sections of CNS tissues by use of one (GM5 and GM6) of three pairs of HHV-6 primers that were selected. Immunohistochemical examination of brain sections, employing a specific monoclonal antibody directed against the HHV-6 gp 102 protein, detected the viral antigen in neurons and glial cells.

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.

Variant-specific tropism of human herpesvirus 6 in human astrocytes

Though first described as a lymphotropic virus, human herpesvirus 6 (HHV-6) is highly neuropathogenic. Two viral variants are known: HHV-6A and HHV-6B. Both variants can infect glial cells and have been differentially associated with central nervous system diseases, suggesting an HHV-6 variant-specific tropism for glial cell subtypes. We have performed infections with both viral variants in human progenitor-derived astrocytes (HPDA) and monitored infected cell cultures for cytopathic effect (CPE), intra- and extracellular viral DNA load, the presence of viral particles by electronic microscopy, mRNA transcription, and viral protein expression. HHV-6A established a productive infection with CPE, visible intracellular virions, and high virus DNA loads. HHV-6B-infected HPDA showed no morphological changes, intracellular viral particles, and decreasing intra- and extracellular viral DNA over time. After long-term passage, HHV-6B-infected HPDA had stable but low levels of intracellular viral DNA load with no detectable viral mRNA. Our results demonstrate that HHV-6A and HHV-6B have differential tropisms and patterns of infection for HPDA in vitro, where HHV-6A results in a productive lytic infection. In contrast, HHV-6B was associated with a nonproductive infection. These findings suggest that HHV-6 variants might be responsible for specific infection patterns in glial cells in vivo. Astrocytes may be an important reservoir for this virus in which differential tropism of HHV-6A and HHV-6B may be associated with different disease outcomes.

Immunology of multiple sclerosis

Multiple sclerosis (MS) develops in young adults with a complex predisposing genetic trait and probably requires an inciting environmental insult such as a viral infection to trigger the disease. The activation of CD4+ autoreactive T cells and their differentiation into a Th1 phenotype are a crucial events in the initial steps, and these cells are probably also important players in the long-term evolution of the disease. Damage of the target tissue, the central nervous system, is, however, most likely mediated by other components of the immune system, such as antibodies, complement, CD8+ T cells, and factors produced by innate immune cells. Perturbations in immunomodulatory networks that include Th2 cells, regulatory CD4+ T cells, NK cells, and others may in part be responsible for the relapsing-remitting or chronic progressive nature of the disease. However, an important paradigmatic shift in the study of MS has occurred in the past decade. It is now clear that MS is not just a disease of the immune system, but that factors contributed by the central nervous system are equally important and must be considered in the future.

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.

Detection of human herpesvirus-6 in mesial temporal lobe epilepsy surgical brain resections

BACKGROUND

Human herpesvirus-6 (HHV-6), a ubiquitous beta-herpesvirus, is the causative agent of roseola infantum and has been associated with a number of neurologic disorders including seizures, encephalitis/meningitis, and multiple sclerosis. Although the role of HHV-6 in human CNS disease remains to be fully defined, a number of studies have suggested that the CNS can be a site for persistent HHV-6 infection.

OBJECTIVE

To characterize the extent and distribution of HHV-6 in human glial cells from surgical brain resections of patients with mesial temporal lobe epilepsy (MTLE).

METHOD

Brain samples from eight patients with MTLE and seven patients with neocortical epilepsy (NE) undergoing surgical resection were quantitatively analyzed for the presence of HHV-6 DNA using a virus-specific real-time PCR assay. HHV-6 expression was also characterized by western blot analysis and in situ immunohistochemistry (IHC). In addition, HHV-6-reactive cells were analyzed for expression of glial fibrillary acidic protein (GFAP) by double immunofluorescence.

RESULTS

DNA obtained from four of eight patients with MTLE had significantly elevated levels of HHV-6 as quantified by real-time PCR. HHV-6 was not amplified in any of the seven patients with NE undergoing surgery. The highest levels of HHV-6 were demonstrated in hippocampal sections (up to 23,079 copies/10(6) cells) and subtyped as HHV-6B. Expression of HHV-6 was confirmed by western blot analysis and IHC. HHV-6 was co-localized to GFAP-positive cells that morphologically appeared to be astrocytes.

CONCLUSIONS

HHV-6B is present in brain specimens from a subset of patients with MTLE and localized to astrocytes in the absence of inflammation. The amplification of HHV-6 from hippocampal and temporal lobe astrocytes of MTLE warrants further investigation into the possible role of HHV-6 in the development of MTLE.

Quantitative analysis of human herpesvirus 6 cell tropism

Although HHV-6A and -6B are known to replicate preferably in human T-lymphocytes, in vitro infection of several other cell types has been described. Also, the finding that both variants use the ubiquitous molecule CD46 as a membrane receptor fully supports the possibility of a broad cellular tropism. However, productive infection, which requires complete progression through the viral replication cycle, depends on multiple cellular processes. Our studies were aimed at determining the differences in replication efficiency according to the cell type infected and at relating these differences to the sequential transcriptional events preceding DNA replication. A strong expression of immediate-early, early, and late genes was only seen in the T-lymphoblastoma lines. In the other cell lines, there was no clear correlation between the level of transcription and the final outcome of replication. Finally, we investigated the cytopathic effects of HHV-6 on different cell types of neural origin (oligodendrocytes, astrocytes, and neurons) in greater detail, and found that although all three sustained HHV-6 replication, HHV-6A was more neurovirulent than HHV-6B. This was confirmed in primary human oligodendrocyte cultures.