Lymphoproliferative responses to human herpesvirus-6 variant A and variant B in healthy adults

Human Herpesvirus 6B Greatly Increases Risk of Depression by Activating Hypothalamic-Pituitary -Adrenal Axis during Latent Phase of Infection

Little is known about the effect of latent-phase herpesviruses on their host. Human herpesvirus 6B (HHV-6B) is one of the most ubiquitous herpesviruses, and olfactory astrocytes are one of the most important sites of its latency. Here, we identified SITH-1, an HHV-6B latent protein specifically expressed in astrocytes. Mice induced to produce SITH-1 in their olfactory astrocytes exhibited olfactory bulb apoptosis, a hyper-activated hypothalamic-pituitary-adrenal (HPA) axis and depressive symptoms. The binding of SITH-1 to the host protein calcium-modulating ligand (CAML) to form an activated complex promoted the influx of extracellular calcium. The serum antibody titers for depressive patients with respect to this activated complex were significantly higher than for normal controls (p = 1.78 × 10⁻¹⁵), when the antibody positive rates were 79.8% and 24.4%, respectively, and the odds ratio was 12.2. These results suggest that, in the latent phase, HHV-6B may be involved in the onset of depression.

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We identified SITH-1, a new protein specific to HHV-6B latent infection

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Mice expressing SITH-1 at HHV-6B latent infection site had depressive symptoms

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Depressive symptoms due to SITH-1 were associated with a hyper-activated HPA axis

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SITH-1-specific antibody detection significantly greater in depressive patients

Latency, Integration, and Reactivation of Human Herpesvirus-6

Human herpesvirus-6A (HHV-6A) and human herpesvirus-6B (HHV-6B) are two closely related viruses that infect T-cells. Both HHV-6A and HHV-6B possess telomere-like repeats at the terminal regions of their genomes that facilitate latency by integration into the host telomeres, rather than by episome formation. In about 1% of the human population, human herpes virus-6 (HHV-6) integration into germline cells allows the viral genome to be passed down from one generation to the other; this condition is called inherited chromosomally integrated HHV-6 (iciHHV-6). This review will cover the history of HHV-6 and recent works that define the biological differences between HHV-6A and HHV-6B. Additionally, HHV-6 integration and inheritance, the capacity for reactivation and superinfection of iciHHV-6 individuals with a second strain of HHV-6, and the role of hypomethylation of human chromosomes during integration are discussed. Overall, the data suggest that integration of HHV-6 in telomeres represent a unique mechanism of viral latency and offers a novel tool to study not only HHV-6 pathogenesis, but also telomere biology. Paradoxically, the integrated viral genome is often defective especially as seen in iciHHV-6 harboring individuals. Finally, gaps in the field of HHV-6 research are presented and future studies are proposed.

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.

Cord-blood hematopoietic stem cell transplant confers an increased risk for human herpesvirus-6-associated acute limbic encephalitis: a cohort analysis

Human herpesvirus-6 (HHV-6) frequently reactivates after allogeneic hematopoietic stem cell transplantation (HSCT); its most severe manifestation is the syndrome of posttransplantation acute limbic encephalitis (HHV-6-PALE). The epidemiology, risk factors, and characteristics of HHV-6-PALE after unrelated cord-blood transplantation (UCBT) are not well characterized. We analyzed 1344 patients undergoing allogeneic HSCT between March 2003 and March 2010 to identify risk factors and characteristics of HHV-6-PALE. The cohort included 1243 adult-donor HSCT and 101 UCBT recipients. All patients diagnosed with HHV-6-PALE had HHV-6 DNA in cerebrospinal fluid (CSF) specimens in addition to symptoms and studies indicating limbic encephalitis. Nineteen cases (1.4%) of HHV-6-PALE were identified during this study: 10 after UCBT (9.9%) and 9 after adult-donor HSCT (0.7%), for an incidence rate of 1.2 cases/1000 patient-days compared to 0.08 cases/1000 patient-days (P < .001), respectively. Risk factors for HHV-6-PALE on multivariable Cox modeling were UCBT (adjusted hazard ratio [aHR], 20.0; 95% confidence interval [CI], 7.3-55.0; P < .001), time-dependent acute graft-versus-host disease (aGVHD) grades II to IV (aHR, 7.5; 95% CI, 2.8-19.8; P < .001), and adult-mismatched donor (aHR, 4.3; 95% CI, 1.1-17.3; P = .04). Death from HHV-6-PALE occurred in 50% of affected patients undergoing UCBT and no recipients of adult-donor cells. Patients receiving UCBT have increased risk for HHV-6-PALE and greater morbidity from this disease.

HHV-6A in syncytial giant-cell hepatitis

Syncytial giant-cell hepatitis is a rare but severe form of hepatitis that is associated with autoimmune diseases, drug reactions, and viral infections. We used serologic, molecular, and immunohistochemical methods to search for an infectious cause in a case of syncytial giant-cell hepatitis that developed in a liver-transplant recipient who had latent infection with variant B of human herpesvirus 6 (HHV-6B) and who had received the organ from a donor with variant A latent infection (HHV-6A). At the onset of the disease, the detection of HHV-6A (but not HHV-6B) DNA in plasma, in affected liver tissue, and in single micromanipulated syncytial giant cells with the use of two different polymerase-chain-reaction (PCR) assays indicated the presence of active HHV-6A infection in the patient. Expression of the HHV-6A-specific early protein, p41/38, but not of the HHV-6B-specific late protein, p101, was demonstrated only in liver syncytial giant cells in the absence of other infectious pathogens. The same markers of HHV-6A active infection were documented in serial follow-up samples from the patient and disappeared only at the resolution of syncytial giant-cell hepatitis. Neither HHV-6B DNA nor late protein was identified in the same follow-up samples from the patient. Thus, HHV-6A may be a cause of syncytial giant-cell hepatitis.

Time course characteristics of human herpesvirus 6 specific cellular immune response and natural killer cell activity in patients with exanthema subitum

The time-course of cell-mediated immunity in exanthema subitum is not well documented. The lymphoproliferative response to purified human herpesvirus 6 (HHV-6) antigen and to phytohemagglutinin was measured and natural killer (NK) cell activities determined in three consecutive specimens obtained biweekly from 18 young children and infants with exanthema subitum. Virus isolation and PCR detection of virus DNA and determination of neutralization antibody to HHV-6 and -7 were also carried out. The magnitude of the HHV-6 specific lymphoproliferative response varied; however, in most cases the time course kinetics revealed a low response in the acute phase with a subsequent gradual increase. In contrast, NK cell activities were high in the acute phase and declined gradually during convalescence. The lymphoproliferative response to phytohemagglutinin did not show a consistent trend in kinetics of time; however, dynamic changes in activity were observed in patients during the acute and convalescent periods. The results suggest that NK cells play a major role in resolving acute phase infection while specific lymphocyte activity develops later. The cause of the delayed development of HHV-6 specific lymphoproliferative response is unknown. The lymphoproliferative response to phytohemagglutinin ratios implied that HHV-6 infection has some impact on host T-cell immunity during the course of exanthema subitum.

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).

Development and evaluation of a flow-cytometric assay of specific cell-mediated immune response in activated whole blood for the detection of cell-mediated immunity against varicella-zoster virus

A new assay for the detection of specific cell-mediated immune (CMI) responses is described. Whole blood, diluted 1/10 in medium, was cultured in the presence or the absence of specific antigens. Results were assessed by flow cytometric analysis with or without immunophenotyping to detect proliferating lymphoblasts among cultured cells. Interferon-gamma, IL-10, and IL-5 in culture supernatants are measured by ELISAs. The assay was evaluated using samples from 37 VZV-antibody-positive children with a history of chickenpox and samples from 15 seronegative children without a history of chickenpox; it displayed a sensitivity of 95% and a specificity of 100% for the detection of varicella-zoster virus (VZV)-specific CMI. The intraassay and interassay variations of the new test were lower than with the conventional assay for CMI, detecting thymidine incorporation in peripheral blood mononuclear cells (PBMCs). Cytokines were detected in only 70% of cultures from VZV-antibody-positive subjects. The cytokine response was restricted to IFN-gamma in most cases. The Flow-cytometric Assay of Specific Cell-mediated Immune response in Activated whole blood (FASCIA) is a precise and accurate yet simple and convenient test that can be readily employed for the examination of single samples as well as for large-scale studies.

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 and distribution of human herpesvirus 6 variants A and B in adult human brain

The presence of human herpesvirus 6 (HHV-6) in brain tissues of 40 consecutive post-mortem cases was examined. For each case, autopsy samples were collected from the cerebellum, frontal, temporal, parietal and occipital lobes of both sides of the brain. HHV-6 DNA was detected by nested polymerase chain reaction and characterised into variants A and B. Overall, 97/400 (24.3%) samples were positive for HHV-6 DNA with 16 being variant A and 81 being variant B, but none of the samples harboured both variants. When analysed by patient, 34/40 (85%) had HHV-6 DNA detected in the brain. The viral DNA positivity did not show significant variation with gender and age. Four patients harboured variant A, 23 harboured variant B, and seven had both variants at different positions. The results indicate that both HHV-6A and HHV-6B are neurotropic and human brain may be another site for latency. HHV-6B was detected in brain tissues of a majority (75%) of the studied population and with a widespread distribution within the brain. Although the observed prevalence of HHV-6A in brain is lower (27.5%), in view of its lower seroprevalence, the neuroinvasive potential of variant A may be comparable to that of variant B. Although both variants are potential pathogens for the nervous system, the fact that they can exist, probably for most of the time, as commensals in human brain needs to be considered when interpreting their roles in neuropathology.

Role of viruses in etiology and pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is the most prevalent demyelinating disease of young adults, affecting an estimated 300,000 individuals in the United States alone. The majority of affected individuals have a relapsing–remitting course while a smaller subset has a more chronic–progressive presentation. Women are affected more often than men, a phenomenon associated with a number of auto-immune diseases. Although the etiology of MS is unknown, it is generally believed that genetic, immunologic, and environmental factors are involved. This chapter discusses these issues as they suggest that exogenous factors are associated with the pathogenesis of this disorder. Recently, the human herpes virus 6 (HHV-6) has received considerable attention as an infectious agent candidate that might be associated with the pathogenesis of MS. The chapter focuses on this agent and the data that support the role of this virus in MS disease pathogenesis. A model is proposed, whereby in genetically susceptible individuals, multiple viruses may trigger either a virus-specific or a cross-reactive auto-immune response that results in clinical MS. Epidemiologic evidence suggests that it is a multifactorial disease that develops as a result of host genetics, immune response, and environment.

Presence of human herpesviruses 6, 7, and 8 DNA sequences in normal brain tissue

The three novel human herpesviruses (HHV) 6, 7, and 8 are predominantly, but not exclusively, lymphotropic. In an attempt to elucidate their neurotropism in vivo, viral DNA sequences present in fresh autopsy cortical brain tissues obtained from 84 consecutive Chinese subjects (mean age, 66.9 years; range, 21-98 years) were detected by a nested polymerase chain reaction. These patients were apparently immunocompetent and free of clinical signs of viral diseases. HHV-6 DNA was detected in 36 of 84 (42.9%) patients, and the DNA-positive and -negative groups did not show a significant difference in age or sex distribution. Of the 36 HHV-6 DNA-positive cases, 9 (25%) were variant A and 27 (75%) were variant B. In view of the lower prevalence of variant A than variant B in the adult population, the two variants may share a comparable neuroinvasive potential. HHV-7 and HHV-8 DNA were detected respectively in three and two patients. The low positive rates of HHV-7 and HHV-8 may represent a relatively lower neuroinvasive potential of the viruses. Alternatively, the localization of HHV-7 and HHV-8 may be more restricted and the sampled cortical tissues may not represent the most abundant site of persistence in the nervous system. The results provide molecular evidence of the presence of the three newly identified herpesviruses in brain tissue. The pathogenic role for HHV-7 and HHV-8, as with HHV-6, in neurological diseases should not be overlooked.

Similar humoral and cellular immunological reactivities to human herpesvirus 6 in patients with multiple sclerosis and controls

Several studies have suggested an association between human herpesvirus 6 (HHV-6) and multiple sclerosis (MS). We have previously studied intrathecal production of antibody to lymphotropic herpesviruses in MS patients and the presence of human herpesvirus 1 to 7 DNAs in cerebrospinal fluid (CSF). In the present study anti-HHV-6 immunoglobulin M (IgM) in serum and anti-HHV-6 IgG subclasses in serum and CSF were examined and the lymphoproliferative response to HHV-6 was analyzed. The PCR examination was refined by purifying DNA from CSF and retesting the samples for HHV-6 DNA. There were no statistically significant differences between the groups concerning IgM positivity, distribution of IgG subclasses, or lymphoproliferative response to HHV-6. The purification of DNA increased the number of PCR-positive samples from 0 of 71 to 4 of 68. The study does not give additional support to the possibility that HHV-6 is a common cause of MS, but a role for the virus in a subset of patients cannot be excluded.