Human herpesvirus 6 is latent in peripheral blood of patients with relapsing-remitting multiple sclerosis

The U94 Gene of Human Herpesvirus 6: A Narrative Review of Its Role and Potential Functions

Human herpesvirus 6 (HHV-6) is a β-herpesvirus that is highly prevalent in the human population. HHV-6 comprises two recognized species (HHV-6A and HHV-6B). Despite different cell tropism and disease association, HHV-6A/B show high genome homology and harbor the conserved U94 gene, which is limited to HHV-6 and absent in all the other human herpesviruses. U94 has key functions in the virus life cycle and associated diseases, having demonstrated or putative roles in virus replication, integration, and reactivation. During natural infection, U94 elicits an immune response, and the prevalence and extent of the anti-U94 response are associated with specific diseases. Notably, U94 can entirely reproduce some virus effects at the cell level, including inhibition of cell migration, induction of cytokines and HLA-G expression, and angiogenesis inhibition, supporting a direct U94 role in the development of HHV-6-associated diseases. Moreover, specific U94 properties, such as the ability to modulate angiogenesis pathways, have been exploited to counteract cancer development. Here, we review the information available on this key HHV-6 gene, highlighting its potential uses.

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.

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.

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.

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.

Human herpesvirus 6 and multiple sclerosis: a one-year follow-up study

BACKGROUND

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

MATERIALS AND METHODS

A one-year follow up study was performed analysing peripheral blood mononuclear cells and serum samples of 57 patients with RRMS and 57 healthy blood donors (HBD) by a quantitative real time PCR, to detect HHV-6 and EBV. Clinical data (starting age and EDSS increase) were collected.

RESULTS

We did not find any statistically significant difference for EBV between RRMS patients and HBD. Regarding HHV-6: i) There was a higher prevalence of HHV-6 in RRMS patients than in controls: 80.7% versus 29.8% respectively. ii) HHV-6 active replication seems to be related to exacerbations. iii) Only variant A was detected among RRMS patients with HHV-6 active replication. iv) Although some difference was found when we compared clinical data in RRMS patients with and without HHV-6 active replication, the results did not reach statistical significance.

CONCLUSIONS

A higher HHV-6A frequency of active infection (reactivation or new infection) would lead to a more frequent exposure of HHV-6A antigens to the immune system of RRMS patients; this active replication of HHV-6A seems to be specifically related with the exacerbations in a subset of RRMS patients.

Kaposi's sarcoma-associated herpesvirus: clinical, diagnostic, and epidemiological aspects

Kaposi's sarcoma-associated herpesvirus (KSHI) is one of the few viruses proven to be associated with tumorigenesis in humans. Its causal association with all clinical and epidemiological variants of Kaposi's sarcoma (KS) is well established. KSHV is also involved in the pathogenesis of primary effusion lymphoma (PEL) and a subset of multicentric Castleman's disease (MCD). Possible associations of KSHV with other clinical settings have been extensively examined. The findings from several of these studies are contradictory and are yet to be resolved. Concentrated effort over the last decade, since the initial discovery of KSHV, led to the development of several experimental systems that resulted in a better comprehension of the biological characteristics of KSHV and set the stage for the understanding of mechainisms by which diseases are induced by the virus. The development of molecular, histological, and serological tools for KSHV diagnosis allowed researchers to track the transmission and to study the epidemiology of KSHV. These assays have been applied, in particular in ambiguous cases, in order to confirm clinically and pathologically based diagnoses. Here, we review the advances in the clinical, experimental, diagnostic, and epidemiological research of KSHV.

Human herpesvirus 6 infects the central nervous system of multiple sclerosis patients in the early stages of the disease

The presence and the replicative state of human herpesvirus 6 (HHV-6) were evaluated in clinical samples from multiple sclerosis (MS) patients at the first time of MS diagnosis. HHV-6 variant B was present in peripheral blood mononuclear cells of 5/32 (15%) patients, but persisted with a latent infection. Viral sequences were present also in cerebrospinal fluid (CSF), both free in the liquid (7/32, 22%) and latent in the cellular fraction (3/32, 9%), as shown by analysis of viral transcription. In these cases, variant A was detected. HHV-6 DNA sequences present in the CSF were associated to mature viral particles. In fact, in vitro infectious assays of CSF showed the presence of replication-competent virions. These results show that about 20% of MS patients have active foci of HHV-6 variant A infection in the early stages of the disease and suggest that viral replication takes place within the central nervous system.

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 antibodies directed against human herpesvirus 6 U94/REP in sera of patients affected by multiple sclerosis

The association between human herpesvirus 6 (HHV-6) and multiple sclerosis (MS) is controversial. In fact, it is difficult to establish a causative role of HHV-6, due to the high prevalence of latently infected individuals in the healthy population. Therefore, the presence of virus sequences in tissue biopsy does not support a viral role, and serological assays do not show significant differences between MS patients and control populations. The only viral gene expressed during latency is U94/rep. Therefore, we have developed a serological assay for the detection of antibodies specifically directed against U94/REP protein. Different populations were analyzed by enzyme-linked immunosorbent assay, including healthy controls, MS patients, and subjects with diseases unrelated to HHV-6 infection, including other neurological diseases. The results show statistically significant differences (P > 0.01) between MS patients and control groups, both in antibody prevalence (87 and 43.9%, respectively) and in geometric mean titer (1:515 and 1:190, respectively). The detection of antibodies specific for HHV-6 U94/REP shows that the immune system is exposed to this antigen during natural infection. The higher prevalence and higher titers of antibodies to U94/REP suggest that MS patients and control groups might experience different exposures to HHV-6.

Human herpes virus 6 and multiple sclerosis

OBJECTIVES

To systematically review the published evidence for a relationship between human herpes virus 6 (HHV-6) and multiple sclerosis (MS).

MATERIALS AND METHODS

The medical literature was searched using MEDLINE and the Cochrane database. Retrieved studies are presented according to the experimental technique(s) used. The studies are rated for quality using a priori defined criteria.

RESULTS

Twenty-eight studies were retrieved. A total of 12 different experimental techniques were used. Four of these techniques provided evidence for a relationship between HHV-6 and MS, but none were able to show a causative relationship.

CONCLUSIONS

The available literature provides some support for a relationship between HHV-6 and MS. The limitations of the available studies and directions for future research are discussed.

Prevalence of herpesvirus DNA in MS patients and healthy blood donors

OBJECTIVES

The aim of this study is to determine the DNA prevalence of different members of Herpesviridae in multiple sclerosis (MS) patients and to describe the possible effect of beta-interferon treatment on such prevalence.

MATERIAL AND METHODS

With a nested polymerase chain reaction (PCR) assay we have studied the DNA of the peripheral blood mononuclear cells (PBMCs) of 204 whole blood samples, [102 from patients with relapsing-remitting MS (RRMS), of which 62 were treated with beta-interferon, and 102 from healthy blood donors].

RESULTS

We only found a statistically significant difference for human herpesvirus type 6 (HHV-6) DNA prevalence (P < 0.0001): HHV-6 is 2.26 times more frequent in MS patients than in healthy donors. There was no difference in the HHV-6 prevalence between beta-interferon treated and untreated patients.

CONCLUSION

1. Among the herpesviruses, HHV-6 was the only one showing altered prevalence. This either indicates that HHV-6 is involved in the pathogenesis of MS, or it simply indicates that MS influences latency or reactivation of HHV-6 without any direct involvement of HHV-6 in the disease process of MS. 2. Treatment with beta-interferon does not make a difference on the DNA prevalence of the herpesviruses studied in our MS patients.

Human herpesvirus 6

The development of techniques for the culture of lymphoid cells and the isolation of viruses that infect these cells led to the discovery of human herpesvirus (HHV) 6 in 1986. At the time, HHV-6 was the first new human herpesvirus to be discovered in roughly a quarter of a century, and its isolation marked the beginning of an era of discovery in herpesvirology, with the identification of HHV-7 and HHV-8 (Kaposi's sarcoma-associated herpesvirus) during the following decade. Like most human herpesviruses, HHV-6 is ubiquitous and capable of establishing a lifelong, latent infection of its host. HHV-6 is particularly efficient at infecting infants and young children, and primary infection with the virus is associated with roseola infantum (exanthem subitum) and, most commonly, an undifferentiated febrile illness. Viral reactivation in the immunocompromised host has been linked to a variety of diseases, including encephalitis, and HHV-6 has been tentatively associated with multiple sclerosis. This article discusses the major properties of HHV-6, its association with human disease, and the pathobiological significance of viral reactivation.

Human herpesvirus 6 and multiple sclerosis: systemic active infections in patients with early disease

By means of immunohistochemical staining, cells actively infected with human herpesvirus 6 (HHV-6) were found in central nervous system tissues from 8 (73%) of 11 patients with definite multiple sclerosis (MS). Interestingly, 17 (90%) of 19 tissue sections showing active demyelination were positive for HHV-6-infected cells compared with only 3 (13%) of 23 tissue sections free of active disease (P<.0001). Central nervous system tissues from 2 of 28 normal persons and patients with other inflammatory demyelinative diseases were positive for HHV-6-infected cells (P<.0001), and the 2 positive cases were diagnosed as having HHV-6 leukoencephalitis. By use of a rapid culture assay, blood samples from 22 (54%) of 41 patients with definite MS were found to contain active HHV-6 infections, compared with 0 of 61 normal controls (P<.0001). No significant difference was found between HHV-6 viremia-positive and HHV-6 viremia-negative MS patients with respect to type of disease (relapsing/remitting or progressive). In contrast, patients with active HHV-6 viremia were significantly younger and had shorter durations of disease than did HHV-6 viremia-negative patients.

Susceptibility to multiple sclerosis: interplay between genes and environment

Multiple sclerosis is a complex trait of unknown etiology. Epidemiological data have shown that susceptibility to multiple sclerosis is determined by both genetic and environmental factors. It is unknown whether the clinical subcategories of multiple sclerosis are separate diseases with separate etiologies and causes. Recent theories of the pathogenesis of multiple sclerosis and candidate genes are discussed. Other potential nonchromosomal factors involved in multiple sclerosis susceptibility such as mitochondrial DNA and viral factors such as Chlamydia pneumoniae are reviewed.