Classification of HHV-6A and HHV-6B as distinct viruses

HHV-6 in liver transplantation: A literature review

Human herpesvirus 6 (HHV-6A and HHV-6B) can cause primary infection or reactivate from latency in liver transplant recipients, which can result in a variety of clinical syndromes, including fever, hepatitis, encephalitis and higher rates of graft dysfunction as well as indirect effects including increased risks of mortality, CMV disease, hepatitis C progression and greater fibrosis scores. Although HHV-6 infection is currently diagnosed by quantifying viral DNA in plasma or blood, biopsy to demonstrate histopathological effects of HHV-6 remains the gold standard for diagnosis of end-organ disease. HHV-6 reactivation may be restricted to the infected organ with no evidence of active infection in the blood. HHV-6 infections in liver transplant patients are mostly asymptomatic, but clinically significant tissue-invasive infections have been treated successfully with ganciclovir, foscarnet or cidofovir. Inherited chromosomally integrated HHV-6 (ciHHV-6), in either the recipient or the donor organ, may create confusion about systemic HHV-6 infection. Recipients with inherited ciHHV-6 may have an increased risk of opportunistic infection and graft rejection. This article reviews the current scientific data on the clinical effects, risk factors, pathogenesis, diagnosis and treatment of HHV-6 infections in liver transplant recipients.

Hypothesis: Is there a link between the immune response to Human Herpes Virus type 6Α (HHV-6Α) infection and the interaction network (interactome) of the genes encoding the CTSS, PTX3, CHI3L1, Mx1, CXCL16, BIRC3 and BST2 proteins?

Human Herpes Virus type 6 (HHV-6) is a ubiquitous virus consisting of two viral species, HHV-6A and HHV-6B that have been associated with numerous and diverse pathologies. As many other viruses HHV-6 modulates the apoptotic machinery of its host to subvert immune response to infection, yet the exact mechanisms behind this process remain under investigation. The genes encoding the CTSS, PTX3, CHI3L1, Mx1, CXCL16, BIRC3 and BST2 proteins have been linked to HHV-6Α related neurologic diseases whilst also associated with apoptosis. This study aimed at the identification and functional analysis of the gene interaction network (interactome) of CTSS-PTX3-CHI3L1-Mx1-CXCL16-BIRC3-BST2 so as to evaluate the hypothesis of a probable link between the latter and host's immune response to HHV-6A infection.

Cytomegalovirus and Other β-Herpesviruses

Cytomegalovirus (CMV), human herpes virus (HHV)-6, and HHV-7 are ubiquitous β-herpesviruses that can cause opportunistic infection and disease in kidney transplant recipients. Active CMV infection and disease are associated with acute allograft failure and death, and HHV-6 and HHV-7 replication are associated with CMV disease. CMV prevention strategies are used commonly after kidney transplantation, and include prophylaxis with antiviral medications and preemptive treatment upon the detection of asymptomatic viral replication in blood. Both approaches decrease CMV disease and allograft rejection, but CMV prophylaxis is preferred for high-risk patients because it is easy to administer and may be more effective in real-world settings. CMV disease commonly occurs even with current preventive strategies, whereas HHV-6 and HHV-7 diseases are rare. The clinical manifestations of CMV, HHV-6, and HHV-7 are nonspecific, and laboratory confirmation is essential to establishing diagnoses. Although nucleic acid testing has supplanted other diagnostic modalities given its high sensitivity and specificity, histopathologic examination sometimes is necessary to identify disease definitively. Ganciclovir and valganciclovir are the treatments of choice for CMV and HHV-6, and foscarnet can be used to treat HHV-7. Treatment duration should be informed by the initial severity of disease, and subsequent clinical and virologic responses.

Glycoproteins of HHV-6A and HHV-6B

Recently, human herpesvirus 6A and 6B (HHV-6A and HHV-6B) were classified into distinct species. Although these two viruses share many similarities, cell tropism is one of their striking differences, which is partially because of the difference in their entry machinery. Many glycoproteins of HHV-6A/B have been identified and analyzed in detail, especially in their functions during entry process into host cells. Some of these glycoproteins were unique to HHV-6A/B. The cellular factors associated with these viral glycoproteins (or glycoprotein complex) were also identified in recent years. Detailed interaction analyses were also conducted, which could partially prove the difference of entry machinery in these two viruses. Although there are still issues that should be addressed, all the knowledges that have been earned in recent years could not only help us to understand these viruses' entry mechanism well but also would contribute to the development of the therapy and/or prophylaxis methods for HHV-6A/B-associated diseases.

Viruses in chronic progressive neurologic disease

Viruses have long been implicated as triggers of disease onset and progression in multiple sclerosis (MS) and similar neuroinflammatory disorders. Decades of epidemiological, molecular, and pathologic studies have most strongly linked the human herpesviruses Epstein-Barr virus (EBV) and human herpesvirus 6 (HHV-6) with MS. However, these viruses are ubiquitous in the general population and typically acquired decades before disease presentation, complicating the study of how they might contribute to disease. As experimental animal models may help elucidate mechanisms that have linked viruses with MS, we have been studying HHV-6 infections in a small nonhuman primate. We recently demonstrated that the subsequent induction of an MS-like experimental neuroinflammatory disease results in significantly accelerated disease in HHV-6 inoculated marmosets compared to controls. Ultimately, disease intervention in the form of clinical trials with an antiviral agent is the best way to concretely demonstrate a role for HHV-6 or any other virus in MS.

Using Droplet Digital PCR to Detect Coinfection of Human Herpesviruses 6A and 6B (HHV-6A and HHV-6B) in Clinical Samples

Droplet digital™ polymerase chain reaction (ddPCR™) is a unique digital PCR technique that allows for absolute quantification of nucleic acid samples. This technique operates on the basis of amplification within water-oil emulsion droplets and can detect very small quantities of target molecules, yielding extremely precise data. Here, we describe in detail a ddPCR procedure for multiplexed detection of two clinically relevant herpesviruses, HHV-6A and HHV-6B.

HHV-6A Infection of Endometrial Epithelial Cells Induces Increased Endometrial NK Cell-Mediated Cytotoxicity

Background: We have recently reported the presence of Human herpesvirus-6A (HHV-6A) DNA in the 43% of endometrial epithelial cells from primary idiopathic infertile women, with no positivity in fertile women. To investigate the possible effect of HHV-6A infection in endometrial (e)NK cells functions, we examined activating/inhibitory receptors expressed by eNK cells and the corresponding ligands on endometrial cells during HHV-6A infection.

Methods: Endometrial biopsies and uterine flushing samples during the secretory phase were obtained from 20 idiopathic infertile women and twenty fertile women. HHV-6A infection of endometrial epithelial cells was analyzed by Real-Time PCR, immunofluorescence and flow cytometry. eNKs receptors and endometrial ligands expression were evaluated by immunofluorescence and flow cytometry.

Results: We observed the presence of HHV-6A infection (DNA, protein) of endometrial epithelial cells in the 40% of idiopathic infertile women. The eNK from all the subgroups expressed high levels of NKG2D and NKG2A receptors. Functional studies showed that NKG2D activating receptor and FasL are involved in the acquired cytotoxic function of eNK cells during HHV-6A infection of endometrial epithelial cells. In the presence of HHV-6A infection, eNK cells increased expression of CCR2, CXCR3 and CX3CR1 chemokine receptors (p = 0.01) and endometrial epithelial cells up-modulated the corresponding ligands: MCP1 (Monocyte chemotactic protein 1, CCL2), IP-10 (Interferon gamma-induced protein 10, CXCL10) and Eotaxin-3 (CCL26).

Conclusion: Our results, for the first time, showed the implication of eNK cells in controlling HHV-6A endometrial infection and clarify the mechanisms that might be implicated in female idiopathic infertility.

The Interplay between Natural Killer Cells and Human Herpesvirus-6

Human Herpesvirus 6 (HHV-6) is a set of two closely related herpes viruses known as HHV-6A and HHV-6B. Both are lymphotropic viruses that establish latency in the host. The ability to evade the immune responses of effector cells is likely a major factor contributing to the development of a persistent HHV-6A/B (collectively termed HHV-6) infection. Natural killer (NK) cells are lymphocytes that, along with neutrophils and monocytes/macrophages, participate in the critical innate immune response during viral infections, but can also mediate the antigen-specific memory responses generally associated with adaptive immunity. NK cells compose the first barrier that viruses must break through to continue replication and dissemination, and a weak NK cell response may predispose an individual to chronic viral infections. Both HHV-6A and HHV-6B can interfere with NK cell-mediated anti-viral responses but the mechanisms by which each of these viruses affect NK cell activity differs. In this review, we will explore the nuanced relationships between the two viruses and NK cells, discussing, in addition, relevant disease associations.

Venture from the Interior-Herpesvirus pUL31 Escorts Capsids from Nucleoplasmic Replication Compartments to Sites of Primary Envelopment at the Inner Nuclear Membrane

Herpesviral capsid assembly is initiated in the nucleoplasm of the infected cell. Size constraints require that newly formed viral nucleocapsids leave the nucleus by an evolutionarily conserved vescular transport mechanism called nuclear egress. Mature capsids released from the nucleoplasm are engaged in a membrane-mediated budding process, composed of primary envelopment at the inner nuclear membrane and de-envelopment at the outer nuclear membrane. Once in the cytoplasm, the capsids receive their secondary envelope for maturation into infectious virions. Two viral proteins conserved throughout the herpesvirus family, the integral membrane protein pUL34 and the phosphoprotein pUL31, form the nuclear egress complex required for capsid transport from the infected nucleus to the cytoplasm. Formation of the nuclear egress complex results in budding of membrane vesicles revealing its function as minimal virus-encoded membrane budding and scission machinery. The recent structural analysis unraveled details of the heterodimeric nuclear egress complex and the hexagonal coat it forms at the inside of budding vesicles to drive primary envelopment. With this review, I would like to present the capsid-escort-model where pUL31 associates with capsids in nucleoplasmic replication compartments for escort to sites of primary envelopment thereby coupling capsid maturation and nuclear egress.

HHV-6A/6B Infection of NK Cells Modulates the Expression of miRNAs and Transcription Factors Potentially Associated to Impaired NK Activity

Natural killer (NK) cells have a critical role in controlling virus infections, and viruses have evolved several mechanisms to escape NK cell functions. In particular, Human herpesvirus 6 (HHV-6) is associated with diseases characterized by immune dysregulation and has been reported to infect NK cells. We recently found that HHV-6 in vitro infection of human thyroid follicular epithelial cells and T-lymphocytes modulates several miRNAs associated with alterations in immune response. Since miRNAs are key regulators of many immune pathways, including NK cell functions, we aimed to study the impact of HHV-6A and -6B in vitro infection on the intracellular mediators correlated to NK cell function. To this purpose, a human NK cell line (NK-92) was infected in vitro with HHV-6A or 6B and analyzed for alterations in the expression of miRNAs and transcription factors. The results showed that both viruses establish lytic replication in NK-92 cells, as shown by the presence of viral DNA, expression of lytic transcripts and antigens, and by the induction of an evident cytopathic effect. Notably, both viruses, although with species-specific differences, induced significant modifications in miRNA expression of miRNAs known for their role in NK cell development, maturation and effector functions (miR-146, miR-155, miR-181, miR-223), and on at least 13 miRNAs with recognized role in inflammation and autoimmunity. Also the expression of transcription factors was significantly modified by HHV-6A/6B infection, with an early increase of ATF3, JUN and FOXA2 by both species, whereas HHV-6A specifically induced a 15-fold decrease of POU2AF1, and HHV-6B an increase of FOXO1 and a decrease of ESR1. Overall, our data show that HHV-6A and -6B infections have a remarkable effect on the expression of miRNAs and transcription factors, which might be important in the induction of NK cell function impairment, virus escape strategies and related pathologies.

Inherited Chromosomally Integrated Human Herpesvirus 6 Genomes Are Ancient, Intact, and Potentially Able To Reactivate from Telomeres

The genomes of human herpesvirus 6A (HHV-6A) and HHV-6B have the capacity to integrate into telomeres, the essential capping structures of chromosomes that play roles in cancer and ageing. About 1% of people worldwide are carriers of chromosomally integrated HHV-6 (ciHHV-6), which is inherited as a genetic trait. Understanding the consequences of integration for the evolution of the viral genome, for the telomere, and for the risk of disease associated with carrier status is hampered by a lack of knowledge about ciHHV-6 genomes. Here, we report an analysis of 28 ciHHV-6 genomes and show that they are significantly divergent from the few modern nonintegrated HHV-6 strains for which complete sequences are currently available. In addition, ciHHV-6B genomes in Europeans are more closely related to each other than to ciHHV-6B genomes from China and Pakistan, suggesting regional variation of the trait. Remarkably, at least one group of European ciHHV-6B carriers has inherited the same ciHHV-6B genome, integrated in the same telomere allele, from a common ancestor estimated to have existed 24,500 ± 10,600 years ago. Despite the antiquity of some, and possibly most, germ line HHV-6 integrations, the majority of ciHHV-6B (95%) and ciHHV-6A (72%) genomes contain a full set of intact viral genes and therefore appear to have the capacity for viral gene expression and full reactivation.

IMPORTANCE Inheritance of HHV-6A or HHV-6B integrated into a telomere occurs at a low frequency in most populations studied to date, but its characteristics are poorly understood. However, stratification of ciHHV-6 carriers in modern populations due to common ancestry is an important consideration for genome-wide association studies that aim to identify disease risks for these people. Here, we present full sequence analysis of 28 ciHHV-6 genomes and show that ciHHV-6B in many carriers with European ancestry most likely originated from ancient integration events in a small number of ancestors. We propose that ancient ancestral origins for ciHHV-6A and ciHHV-6B are also likely in other populations. Moreover, despite their antiquity, all of the ciHHV-6 genomes appear to retain the capacity to express viral genes, and most are predicted to be capable of full viral reactivation. These discoveries represent potentially important considerations in immunocompromised patients, in particular in organ transplantation and in stem cell therapy.

Age-Related Macular Degeneration: A Connection between Human Herpes Virus-6A-Induced CD46 Downregulation and Complement Activation?

Viruses are able to interfere with the immune system by docking to receptors on host cells that are important for proper functioning of the immune system. A well-known example is the human immunodeficiency virus that uses CD4 cell surface molecules to enter host lymphocytes and thereby deleteriously destroying the helper cell population of the immune system. A more complicated mechanism is seen in multiple sclerosis (MS) where human herpes virus-6A (HHV-6A) infects astrocytes by docking to the CD46 surface receptor. Such HHV-6A infection in the brain of MS patients has recently been postulated to enable Epstein-Barr virus (EBV) to transform latently infected B-lymphocytes in brain lesions leading to the well-known phenomenon of oligoclonal immunoglobulin production that is widely used in the diagnosis of MS. The cellular immune response to HHV-6A and EBV is one part of the pathogenic mechanisms in MS. A more subtle pathogenic mechanism can be seen in the downregulation of CD46 on astrocytes by the infecting HHV-6A. Since CD46 is central in regulating the complement system, a lack of CD46 can lead to hyperactivation of the complement system. In fact, activation of the complement system in brain lesions is a well-known pathogenic mechanism in MS. In this review, it is postulated that a similar mechanism is central in the development of age-related macular degeneration (AMD). One of the earliest changes in the retina of AMD patients is the loss of CD46 expression in the retinal pigment epithelial (RPE) cells in the course of geographic atrophy. Furthermore, CD46 deficient mice spontaneously develop dry-type AMD-like changes in their retina. It is also well known that certain genetic polymorphisms in the complement-inhibiting pathways correlate with higher risks of AMD development. The tenet is that HHV-6A infection of the retina leads to downregulation of CD46 and consequently to hyperactivation of the complement system in the eyes of susceptible individuals.

Crystal Structure of the DNA-Binding Domain of Human Herpesvirus 6A Immediate Early Protein 2

Immediate early proteins of human herpesvirus 6A (HHV-6A) are expressed at the outset of lytic infection and thereby regulate viral gene expression. Immediate early protein 2 (IE2) of HHV-6A is a transactivator that drives a variety of promoters. The C-terminal region of HHV-6A IE2 is shared among IE2 homologs in betaherpesviruses and is involved in dimerization, DNA binding, and transcription factor binding. In this study, the structure of the IE2 C-terminal domain (IE2-CTD) was determined by X-ray crystallography at a resolution of 2.5 Å. IE2-CTD forms a homodimer stabilized by a β-barrel core with two interchanging long loops. Unexpectedly, the core structure resembles those of the gammaherpesvirus factors EBNA1 of Epstein-Barr virus and LANA of Kaposi sarcoma-associated herpesvirus, but the interchanging loops are longer in IE2-CTD and form helix-turn-helix (HTH)-like motifs at their tips. The HTH and surrounding α-helices form a structural feature specific to the IE2 group. The apparent DNA-binding site (based on structural similarity with EBNA1 and LANA) resides on the opposite side of the HTH-like motifs, surrounded by positive electrostatic potential. Mapping analysis of conserved residues on the three-dimensional structure delineated a potential factor-binding site adjacent to the expected DNA-binding site. The predicted bi- or tripartite functional sites indicate a role for IE2-CTD as an adapter connecting the promoter and transcriptional factors that drive gene expression.IMPORTANCE Human herpesvirus 6A (HHV-6A) and HHV-6B belong to betaherpesvirus subfamily. Both viruses establish lifelong latency after primary infection, and their reactivation poses a significant risk to immunocompromised patients. Immediate early protein 2 (IE2) of HHV-6A and HHV-6B is a transactivator that triggers viral replication and contains a DNA-binding domain shared with other betaherpesviruses such as human herpesvirus 7 and human cytomegalovirus. In this study, an atomic structure of the DNA-binding domain of HHV-6A IE2 was determined and analyzed, enabling a structure-based understanding of the functions of IE2, specifically DNA recognition and interaction with transcription factors. Unexpectedly, the dimeric core resembles the DNA-binding domain of transcription regulators from gammaherpesviruses, showing structural conservation as a DNA-binding domain but with its own unique structural features. These findings facilitate further characterization of this key viral transactivator.

EBV and HHV-6 Circulating Subtypes in People Living with HIV in Burkina Faso, Impact on CD4 T cell count and HIV Viral Load

Epstein Barr Virus (EBV) and Human Herpes Virus 6 (HHV-6) are responsible for severe diseases, particularly in immunocompromised persons. There is limited data of the infection of these opportunistic viruses in Burkina Faso.

The purpose of this study was to characterize EBV and HHV-6 subtypes and to assess their impact on CD4 T cell count, HIV-1 viral load and antiretroviral treatment in people living with HIV-1. The study population consisted of 238 HIV-positive patients with information on the CD4 T cell count, HIV-1 viral load and HAART. Venous blood samples collected in EDTA tubes were used for EBV and HHV-6 Real Time PCR subtyping.

An infection rate of 6.7% (16/238) and 7.1% (17/238) were found respectively for EBV and HHV-6 in the present study. Among EBV infections, similar prevalence was noted for both subtypes (3.9% (9/238) for EBV-1 vs 4.6% (11/238) for EBV-2) with 2.1% (5/238) of co-infection. HHV-6A infection represented 6.3% (15/238) of the study population against 5.0% (12/238) for HHV-6B. EBV-2 infection was significantly higher in patients with CD4 T cell count ≥ 500 compared to those with CD4 T cell count less than 500 cells (1.65% vs 8.56%, p = 0,011). The prevalence of EBV and HHV-6 infections was almost similar in HAART-naive and HAART-experienced patients.

The present study provides information on the prevalence of EBV and HHV-6 subtypes in people living with HIV-1 in Burkina Faso. The study also suggests that HAART treatment has no effect on infection with these opportunistic viruses in people living with HIV-1.

Chemokines encoded by herpesviruses

Viruses use diverse strategies to elude the immune system, including copying and repurposing host cytokine and cytokine receptor genes. For herpesviruses, the chemokine system of chemotactic cytokines and receptors is a common source of copied genes. Here, we review the current state of knowledge about herpesvirus-encoded chemokines and discuss their possible roles in viral pathogenesis, as well as their clinical potential as novel anti-inflammatory agents or targets for new antiviral strategies.

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.

Telomeres and Telomerase: Role in Marek's Disease Virus Pathogenesis, Integration and Tumorigenesis

Telomeres protect the ends of vertebrate chromosomes from deterioration and consist of tandem nucleotide repeats (TTAGGG)_n that are associated with a number of proteins. Shortening of the telomeres occurs during genome replication, thereby limiting the replication potential of somatic cells. To counteract this shortening, vertebrates encode the telomerase complex that maintains telomere length in certain cell types via de novo addition of telomeric repeats. Several herpesviruses, including the highly oncogenic alphaherpesvirus Marek's disease virus (MDV), harbor telomeric repeats (TMR) identical to the host telomere sequences at the ends of their linear genomes. These TMR facilitate the integration of the MDV genome into host telomeres during latency, allowing the virus to persist in the host for life. Integration into host telomeres is critical for disease and tumor induction by MDV, but also enables efficient reactivation of the integrated virus genome. In addition to the TMR, MDV also encodes a telomerase RNA subunit (vTR) that shares 88% sequence identity with the telomerase RNA in chicken (chTR). vTR is highly expressed during all stages of the virus lifecycle, enhances telomerase activity and plays an important role in MDV-induced tumor formation. This review will focus on the recent advances in understanding the role of viral TMR and vTR in MDV pathogenesis, integration and tumorigenesis.

Complete genome sequence of Ostreid herpesvirus type 1 µVar isolated during mortality events in the Pacific oyster Crassostrea gigas in France and Ireland

Infections with Ostreid herpesvirus 1 (OsHV-1) microvariants in young Pacific oysters are associated with massive mortality events and significant economic losses. Previous studies, focusing on few regions of the genome, have revealed the genomic diversity of these genotypes with respect to the reference type. We used a NGS process to sequence the whole genome of the OsHV-1 µVar in infected individuals, collected during mortality events in France and Ireland. The final genome length of OsHV-1 µVar was approximately 205kbp, shorter than the reference genotype and the overall genome organisation resembled herpes simplex viruses. 94.4% similarity was observed with the OsHV-1 reference genotype. Large indels, including five deletions and three insertions were found to induce the loss and the addition of several ORFs, summed with codon substitutions in 64% of genes shared with the reference type. This diversity raises the question of the exact origin and evolution of OsHV-1 µVar.

Human Herpesviruses 6A, 6B, and 7

Human roseoloviruses include three different species, human herpesviruses 6A, 6B, and 7 (HHV-6A, HHV-6B, HHV-7), genetically related to human cytomegalovirus. They exhibit a wide cell tropism in vivo and, like other herpesviruses, induce a lifelong latent infection in humans. In about 1% of the general population, HHV-6 DNA is covalently integrated into the subtelomeric region of cell chromosomes (ciHHV-6). Many active infections, corresponding to primary infections, reactivations, or exogenous reinfections, are asymptomatic. They also may cause serious diseases, particularly in immunocompromised individuals, including hematopoietic stem-cell transplant (HSCT) and solid-organ transplant recipients, and acquired immunodeficiency syndrome (AIDS) patients. This opportunistic pathogenic role is formally established for HHV-6 infection and less clear for HHV-7. It mainly concerns the central-nervous system, bone marrow, lungs, gastrointestinal tract, skin, and liver. As the best example, HHV-6 causes both exanthema subitum, a benign disease associated with primary infection, and severe encephalitis associated with virus reactivations in HSCT recipients. Diagnosis using serologic and direct antigen-detection methods currently exhibits limitations. The most prominent technique is the quantification of viral DNA in blood, other body fluids, and organs by means of real-time polymerase-chain reaction (PCR). The antiviral compounds ganciclovir, foscarnet, and cidofovir are effective against active infections, but there is currently no consensus regarding the indications of treatment or specifics of drug administration. Numerous questions about HHV-6A, HHV-6B, HHV-7 are still pending, concerning in particular clinical impact and therapeutic options in immunocompromised patients.

Stabilization of Telomere G-Quadruplexes Interferes with Human Herpesvirus 6A Chromosomal Integration

Human herpesviruses 6A and 6B (HHV-6A/B) can integrate their genomes into the telomeres of human chromosomes using a mechanism that remains poorly understood. To achieve a better understanding of the HHV-6A/B integration mechanism, we made use of BRACO-19, a compound that stabilizes G-quadruplex secondary structures and prevents telomere elongation by the telomerase complex. First, we analyzed the folding of telomeric sequences into G-quadruplex structures and their binding to BRACO-19 using G-quadruplex-specific antibodies and surface plasmon resonance. Circular dichroism studies indicate that BRACO-19 modifies the conformation and greatly stabilizes the G-quadruplexes formed in G-rich telomeric DNA. Subsequently we assessed the effects of BRACO-19 on the HHV-6A initial phase of infection. Our results indicate that BRACO-19 does not affect entry of HHV-6A DNA into cells. We next investigated if stabilization of G-quadruplexes by BRACO-19 affected HHV-6A's ability to integrate its genome into host chromosomes. Incubation of telomerase-expressing cells with BRACO-19, such as HeLa and MCF-7, caused a significant reduction in the HHV-6A integration frequency (P < 0.002); in contrast, BRACO-19 had no effect on HHV-6 integration frequency in U2OS cells that lack telomerase activity and elongate their telomeres through alternative lengthening mechanisms. Our data suggest that the fluidity of telomeres is important for efficient chromosomal integration of HHV-6A and that interference with telomerase activity negatively affects the generation of cellular clones containing integrated HHV-6A.IMPORTANCE HHV-6A/B can integrate their genomes into the telomeres of infected cells. Telomeres consist of repeated hexanucleotides (TTAGGG) of various lengths (up to several kilobases) and end with a single-stranded 3' extension. To avoid recognition and induce a DNA damage response, the single-stranded overhang folds back on itself and forms a telomeric loop (T-loop) or adopts a tertiary structure, referred to as a G-quadruplex. In the current study, we have examined the effects of a G-quadruplex binding and stabilizing agent, BRACO-19, on HHV-6A chromosomal integration. By stabilizing G-quadruplex structures, BRACO-19 affects the ability of the telomerase complex to elongate telomeres. Our results indicate that BRACO-19 reduces the number of clones harboring integrated HHV-6A. This study is the first of its kind and suggests that telomerase activity is essential to restore a functional telomere of adequate length following HHV-6A integration.

HHV-6A/B Integration and the Pathogenesis Associated with the Reactivation of Chromosomally Integrated HHV-6A/B

Unlike other human herpesviruses, human herpesvirus 6A and 6B (HHV-6A/B) infection can lead to integration of the viral genome in human chromosomes. When integration occurs in germinal cells, the integrated HHV-6A/B genome can be transmitted to 50% of descendants. Such individuals, carrying one copy of the HHV-6A/B genome in every cell, are referred to as having inherited chromosomally-integrated HHV-6A/B (iciHHV-6) and represent approximately 1% of the world's population. Interestingly, HHV-6A/B integrate their genomes in a specific region of the chromosomes known as telomeres. Telomeres are located at chromosomes' ends and play essential roles in chromosomal stability and the long-term proliferative potential of cells. Considering that the integrated HHV-6A/B genome is mostly intact without any gross rearrangements or deletions, integration is likely used for viral maintenance into host cells. Knowing the roles played by telomeres in cellular homeostasis, viral integration in such structure is not likely to be without consequences. At present, the mechanisms and factors involved in HHV-6A/B integration remain poorly defined. In this review, we detail the potential biological and medical impacts of HHV-6A/B integration as well as the possible chromosomal integration and viral excision processes.

Human herpes virus 6 infection in pediatric organ transplant patients

Transplant patients need lifelong immunosuppressive medication, but this reduces their defense mechanisms, making them prone to viral infections and reactivations. We aimed to clarify the prevalence and clinical manifestations of the human herpes virus 6 (HHV-6) infection in children after pediatric solid organ transplants. Clinical findings and viral loads were compared between primary HHV-6 infections and reactivations. The study comprised 47 kidney, 25 liver, and 12 heart transplant patients who underwent surgery from 2009 to 2014. HHV-6 antibodies were analyzed before surgery, and HHV-6 DNAemia tests were regularly carried out after the transplant using a real-time quantitative polymerase chain reaction method. We found the primary HHV-6 infection in 19 of 22 (86%) seronegative patients, and it was more common in patients under 3 years of age (79%) than over 3 (38%, P=.0002). Post-transplant HHV-6 DNAemia affected 48 of 84 (57%) patients and was significantly higher in primary infections than reactivations (P=.001), and 17 of 48 (35%) patients had symptoms when it was detected at a median of 2 weeks post-transplant. The HHV-6 infection was common after solid organ transplants, especially under 3 years of age, and it typically started 2 weeks after surgery. Testing for HHV-6 DNAemia is recommended shortly after transplantation, especially in patients with fever, diarrhea, rash, seizures, or abnormal liver enzyme tests.

Human Herpesvirus 6A Exhibits Restrictive Propagation with Limited Activation of the Protein Kinase R-eIF2α Stress Pathway

The eIF2α protein plays a critical role in the regulation of translation. The production of double-stranded RNA (dsRNA) during viral replication can activate protein kinase R (PKR), which phosphorylates eIF2α, leading to inhibition of the initial step of translation. Many viruses have evolved gene products targeting the PKR-eIF2a pathway, indicating its importance in antiviral defense. In the present study, we focused on alternations of PKR-eIF2a pathway during human herpesvirus 6A (HHV-6A) infection while monitoring viral gene expression and infectious viral yields. We have found increased phosphorylated PKR as well as phosphorylated eIF2α coincident with accumulation of the late gp82-105 viral protein. The level of total PKR was relatively constant, but it decreased by 144 h postinfection. The phosphorylation of eIF2a led to a moderate increase in activating transcription factor 4 (ATF4) accumulation, indicating moderate inhibition of protein translation during HHV-6A infection. The overexpression of PKR led to decreased viral propagation coincident with increased accumulation of phosphorylated PKR and phosphorylated eIF2a. Moreover, addition of a dominant negative PKR mutant resulted in a moderate increase in viral replication. HHV-6A exhibits relatively low efficiency of propagation of progeny virus secreted into the culture medium. This study suggests that the replicative strategy of HHV-6A involves a mild infection over a lengthy life cycle in culture, while preventing severe activation of the PKR-eIF2α pathway.

IMPORTANCE Human herpesvirus 6A (HHV-6A) and HHV-6B are common, widely prevalent viruses, causing from mild to severe disease. Our study focused on the PKR-eIF2α stress pathway, which limits viral replication. The HHV-6 genome carries multiple genes transcribed from the two strands, predicting accumulation of dsRNAs which can activate PKR and inhibition of protein synthesis. We report that HHV-6A induced the accumulation of phosphorylated PKR and phosphorylated eIF2α and a moderate increase of activating transcription factor 4 (ATF4), which is known to transcribe stress genes. Overexpression of PKR led to increased eIF2α phosphorylation and decreased viral replication, whereas overexpression of a dominant negative PKR mutant resulted in a moderate increase in viral replication. These results suggest that the HHV-6A replication strategy involves restricted activation of the PKR-eIF2α pathway, partial translation inhibition, and lower yields of infectious virus. In essence, HHV-6A limits its own replication due to the inability to bypass the eIF2α phosphorylation.

Purification, Crystallization and X-ray Diffraction Study of the C-terminal Domain of Human Herpesvirus 6A Immediate Early Protein 2

Human herpesvirus 6A (HHV-6A) starts its replication cycle following the action of immediate early proteins that transactivate viral promoters. Immediate early protein 2 (IE2) of HHV-6A is a 1500 amino acid polypeptide with a C-terminal region that is conserved among beta-herpesvirus subfamily members. In this study, a structural domain in the homologous C-terminal region was subjected to secondary structure prediction, and residues 1324-1500 were subsequently designated as the C-terminal domain of IE2 (IE2-CTD). The gene fragment encoding IE2-CTD was inserted into an E. coli expression vector and expressed as a fusion protein with maltose binding protein (MBP) at the N-terminus. IE2-CTD has a theoretical isoelectric point (pI) of 9.29, and strong cation exchange column chromatography was effective for purification. Needle-shaped crystals of IE2-CTD were obtained using the sitting-drop vapour diffusion method, and larger selenomethionine-labelled crystals of space group P2₁ diffracted X-rays to 2.5 Å resolution using synchrotron radiation. Data were collected at the selenium absorption peak wavelength for experimental phasing by the single anomalous dispersion method. The resulting electron density map clearly shows the protein backbone, and full structural determination and refinement are in progress.

Detection of inherited chromosomally integrated HHV-6 (ciHHV-6) in a marker chromosome

OBJECTIVES

Inherited chromosomally integrated human herpesvirus-6 (ciHHV-6) is characterised by the complete HHV-6 genome integration into the host germ line genome and is vertically transmitted with a Mendelian inheritance. By now, the only relationship between ciHHV-6 and diseases seems to be with angina pectoris.

METHODS

We report a case of an 82-year-old man diagnosed with diffuse large B-cell lymphoma (DLBCL) on October 2014. To substantiate the suspicion of ciHHV-6, we analysed peripheral blood mononuclear cells, bone marrow biopsy and pleural effusion-derived mesothelial cells with PCR, RT-PCR and FISH.

RESULTS

Virological routine screening by PCR showed the absence of HHV-8 and EBV infections, while the presence of HHV-6 DNA (ie, U22, U42 and U94 HHV-6 genes), with a viral load of about 1.0 genome per cell, strongly suggests ciHHV-6. The RT-PCR showed the positivity only for the immediate-early U94, at low levels of transcription (100±15 transcripts/1 μg RNA). FISH analysis reported a case of inherited ciHHV-6 in 17p chromosome region and, for the first time, in a marker chromosome.

CONCLUSIONS

This is the first case of inherited ciHHV-6 in a marker chromosome, possibly elucidating the role of this abnormality in the biology of DLBCL.

Increased interleukin-1β and basic fibroblast growth factor levels in the cerebrospinal fluid during human herpesvirus-6B (HHV-6B) encephalitis

Human herpesvirus 6B (HHV-6B) causes exanthema subitum in infants and is known to be mildly pathogenic. However, HHV-6B infection can induce febrile seizures in a high percentage of patients, and in rare cases, result in encephalitis. We detected higher levels of interleukin (IL)-1β and basic fibroblast growth factor (bFGF) in the cerebrospinal fluid (CFS) of patients with HHV-6B encephalitis when compared to those in patients with non-HHV-6B-induced febrile seizures. In vitro, IL-1β and bFGF enhanced HHV-6B gene expression in infected U373 astrocytes during the initial and maintenance phases of infection, respectively. These findings indicated that IL-1β and bFGF contribute to HHV-6B growth and the onset of encephalitis.

Human herpesvirus 6 lymphadenitis in drug rash with eosinophilia and systemic symptoms syndrome: a lymphoma mimic

AIMS

Lymphadenopathy, haematological abnormalities and constitutional symptoms are among the non-specific manifestations seen in drug rash with eosinophilia and systemic symptoms (DRESS), an uncommon but potentially fatal cutaneous adverse drug reaction. The ubiquitous human herpesvirus 6 (HHV-6) plays a unique role in the pathogenesis of DRESS, with emerging data suggesting that reactivation occurs in most cases and contributes to the clinical manifestations, including lymphadenopathy. Further, in the appropriate clinical context, demonstration of HHV-6 reactivation may lend support to a diagnosis of DRESS. The histopathology of DRESS-associated HHV-6 lymphadenitis is reported rarely, with morphologic and immunophenotypic characteristics concerning for T cell lymphoma. The aim is to characterize the histopathology of HHV-6 lymphadenitis in the context of DRESS and to highlight this as an important cause of lymphadenopathy that may be a clinical, morphologic and immunophenotypic mimic of lymphoma.

METHODS AND RESULTS

We describe a case of lymphoma-mimicking lymphadenitis in which the histopathological demonstration of reactivation of HHV-6 infection lent support to the clinical diagnosis of DRESS.

CONCLUSION

Lymph node biopsies concerning for T cell lymphoma should be evaluated for HHV-6 involvement in a clinical context suggestive of DRESS.

Multiple sclerosis: an example of pathogenic viral interaction?

A hypothesis is formulated on viral interaction between HHV-6A and EBV as a pathogenic mechanism in Multiple Sclerosis (MS). Evidence of molecular and genetic mechanisms suggests a link between HHV-6A infection and EBV activation in the brain of MS patients leading to intrathecal B-cell transformation. Consequent T-cell immune response against the EBV-infected cells is postulated as a pathogenic basis for inflammatory lesion formation in the brain of susceptible individuals. A further link between HHV-6A and EBV involves their induction of expression of the human endogenous retrovirus HERV-K18-encoded superantigen. Such virally induced T-cell responses might secondarily also lead to local autoimmune phenomena. Finally, research recommendations are formulated for substantiating the hypothesis on several levels: epidemiologically, genetically, and viral expression in the brain.

Roseolovirus-associated encephalitis in immunocompetent and immunocompromised individuals

The roseoloviruses, human herpesvirus (HHV)-6A, HHV-6B, and HHV-7, can cause severe encephalitis or encephalopathy. In immunocompetent children, primary HHV-6B infection is occasionally accompanied by diverse clinical forms of encephalitis. Roseolovirus coinfections with heterologous viruses and delayed primary HHV-7 infection in immunocompetent adults result in very severe neurological and generalized symptoms. Recovery from neurological sequelae is slow and sometimes incomplete. In immunocompromised patients with underlying hematological malignancies and transplantation, frequent single or simultaneous reactivation of roseoloviruses elicit severe, lethal organ dysfunctions, including damages in the limbic system, brain stem, and hippocampus. Most cases have been due to HHV-6B with HHV-6A accounting for 2-3%. The most severe manifestation of HHV-6B reactivation is post-transplantation limbic encephalitis. Seizures, cognitive problems, and abnormal EEG are common. Major risk factors for HHV-6B-associated encephalitis include unrelated cord blood cell transplantation and repeated hematopoietic stem cell transplantation. Rare genetic disorders, male gender, certain HLA constellation, and immune tolerance to replicating HHV-6 in persons carrying chromosomally integrated HHV-6 might also predispose an individual to roseolovirus-associated brain damage. At this time, little is known about the risk factors for HHV-7-associated encephalitis. Intrathecal glial cell destruction due to virus replication, overexpression of proinflammatory cytokines, and viral mimicry of chemokines all contribute to brain dysfunction. High virus load in the cerebrospinal fluid, hippocampal astrogliosis, and viral protein expression in HHV-6B-associated cases and multiple microscopic neuronal degeneration in HHV-7-associated cases are typical laboratory findings. Early empirical therapy with ganciclovir or foscarnet might save the life of a patient with roseolovirus-associated encephalitis.

HHV-6A in vitro infection of thyrocytes and T cells alters the expression of miRNA associated to autoimmune thyroiditis

Background

Human herpesviruses have been hypothesized as environmental triggers in the development of autoimmune thyroid diseases (AITD), and in particular active human herpesvirus 6A (HHV-6A) infection was detected in thyrocytes of Hashimoto’s thyroiditis (HT) patients, who also show specific anti-viral immune responses. On the other hand, AITD patients display modulation of specific miRNAs in thyroid tissue and blood. We wanted to ascertain whether HHV-6A infection might be correlated to the miRNA dysregulation observed in AITD.

Methods

Human thyroid and T-cell lines were infected in vitro with HHV-6A,-6B or −7, and analysed for miRNAs expression, either by microarray or by specific RT-PCR assays detecting miRNAs associated with AITD in vivo.

Results

HHV-6A infection, but not -6B or −7 infections, induced a decrease in miR-155_2 expression and an increase in miR-1238 expression in thyrocytes, as well as an increase in the expression levels of several autoimmunity-associated miRNAs in T lymphocytes, including miR-16_1, miR34a, miR-130a, miR-143_1, miR-202, miR-301b, miR-302c, miR-449b, miR-451_1, and miR-1238_2.

Conclusions

HHV-6A infection modulates miRNAs expression in the cell types involved in the development of AITD. Notably, our in vitro findings correlate with what observed in AITD patients, further supporting the association between HHV-6A infection and AITD development. Moreover, these effects are 6A-specific, emphasizing the differences between the two HHV-6 virus species, and suggesting diverse virus mechanisms of action and therapeutic approaches.

Divergent tropism of HHV-6AGS and HHV-6BPL1 in T cells expressing different CD46 isoform patterns

CD46 is a receptor for HHV-6A, but its role as a receptor for HHV-6B is controversial. The significance of CD46 isoforms for HHV-6A and HHV-6B tropism is unknown. HHV-6A_GS was able to initiate transcription of the viral genes U7 and U23 in the CD46⁺CD134^- T-cell lines Peer, Jurkat, Molt3, and SupT1, whereas HHV-6B_PL1 was only able to do so in Molt3 and SupT1, which expressed a CD46 isoform pattern different from Peer and Jurkat. The HHV-6B_PL1-susceptible T-cell lines were characterized by low expression of the CD46 isoform BC2 and domination of isoforms containing the cytoplasmic tail, CYT-1. A HHV-6B_PL1 susceptible cell line, Be13, changed over time its CD46 isoform pattern to resemble Peer and Jurkat and concomitantly lost its susceptibility to HHV-6B_PL1 but not HHV-6A_GS infection. We propose that isoforms of CD46 impact on HHV-6B infection and thereby in part explain the distinct tropism of HHV-6A_GS and HHV-6B_PL1.

Update on infections with human herpesviruses 6A, 6B, and 7

Human herpesviruses 6A, 6B, and 7 (HHV-6A, HHV-6B, HHV-7) are genetically related to cytomegalovirus. They belong to the Roseolovirus genus and to the Betaherpesvirinae subfamily. They infect T cells, monocytes-macrophages, epithelial cells, and central nervous system cells. These viruses are ubiquitous and are responsible for lifelong chronic infections, most often asymptomatic, in the vast majority of the general adult population. HHV-6B is responsible for exanthema subitum, which is a benign disease of infants. HHV-6A and HHV-6B also cause opportunistic infections in immunocompromised patients: encephalitis, hepatitis, bone marrow suppression, colitis, and pneumonitis. Their etiological role in chronic diseases such as multiple sclerosis, cardiomyopathy, and thyroiditis is still controversial. The pathogenicity of HHV-7 is less clear and seems to be much more restricted. Chromosomal integration of HHV-6A and HHV-6B is transmissible from parents to offspring and observed in about 1% of the general population. This integration raises the question of potential associated diseases and can be a confounding factor for the diagnosis of active infections by both viruses. The diagnosis of HHV-6A, HHV-6B, and HHV-7 infections is rather based on gene amplification (PCR), which allows for the detection and quantification of the viral genome, than on serology, which is mainly indicated in case of primary infection. Ganciclovir, foscarnet, and cidofovir inhibit the replication of HHV-6A, HHV-6B, and HHV-7. Severe infections may thus be treated but these therapeutic indications are still poorly defined.

Human Herpesvirus 6B Downregulates Expression of Activating Ligands during Lytic Infection To Escape Elimination by Natural Killer Cells

The Herpesviridae family consists of eight viruses, most of which infect a majority of the human population. One of the less-studied members is human herpesvirus 6 (HHV-6) (Roseolovirus), which causes a mild, well-characterized childhood disease. Primary HHV-6 infection is followed by lifelong latency. Reactivation frequently occurs in immunocompromised patients, such as those suffering from HIV infection or cancer or following transplantation, and causes potentially life-threatening complications. In this study, we investigated the mechanisms that HHV-6 utilizes to remain undetected by natural killer (NK) cells, which are key participants in the innate immune response to infections. We revealed viral mechanisms which downregulate ligands for two powerful activating NK cell receptors: ULBP1, ULBP3, and MICB, which trigger NKG2D, and B7-H6, which activates NKp30. Accordingly, this downregulation impaired the ability of NK cells to recognize HHV-6-infected cells. Thus, we describe for the first time immune evasion mechanisms of HHV-6 that protect lytically infected cells from NK elimination.

IMPORTANCE

Human herpesvirus 6 (HHV-6) latently infects a large portion of the human population and can reactivate in humans lacking a functional immune system, such as cancer or AIDS patients. Under these conditions, it can cause life-threatening diseases. To date, the actions and interplay of immune cells, and particularly cells of the innate immune system, during HHV-6 infection are poorly defined. In this study, we aimed to understand how cells undergoing lytic HHV-6 infection interact with natural killer (NK) cells, innate lymphocytes constituting the first line of defense against viral intruders. We show that HHV-6 suppresses the expression of surface proteins that alert the immune cells by triggering two major receptors on NK cells, NKG2D and NKp30. As a consequence, HHV-6 can replicate undetected by the innate immune system and potentially spread infection throughout the body. This study advances the understanding of HHV-6 biology and the measures it uses to successfully escape immune elimination.

CD4+ T Cells Coexpressing CD134 (OX40) Harbor Significantly Increased Levels of Human Herpesvirus 6B DNA Following Umbilical Cord Blood Transplantation

Human herpesvirus 6B (HHV-6B) commonly reactivates after umbilical cord blood transplantation (UCBT) and is associated with delayed engraftment, fever, rash, and central nervous system dysfunction. Recently, CD134 (OX40) has been implicated as a potential viral entry receptor. We evaluated CD4⁺CD134⁺/^neg-lo and CD8⁺CD134⁺/^neg-lo cells at day 28 after UCBT in 20 subjects with previously documented HHV-6 reactivation and persistent viremia. Analysis of CD4⁺CD134⁺ cells as compared to CD4⁺CD134^neg-lo cells showed 0.308 versus 0.129 copies of HHV-6B/cell (P = .0002). CD8⁺CD134^+/neg-lo cells contained little to no HHV-6B copies. Following UCBT, CD4⁺CD134⁺ cells harbor significantly increased levels of HHV-6B, suggesting that CD134 (OX40) may facilitate viral entry.

Association of active human herpesvirus-6 (HHV-6) infection with autoimmune thyroid gland diseases

OBJECTIVES

Viral infections frequently have been cited as important environmental factors implicated in the onset of autoimmune thyroiditis (AIT). The aim of this study was to determine the involvement of HHV-6 infection in the development of autoimmune thyroiditis.

METHODS

This study included 45 patients (42 female and 3 male; median age 47.00 IQR 38.50-57.00) with histologically, laboratory, and clinically confirmed autoimmune thyroiditis, as well as 30 autopsied subjects (26 female and 4 male; median age 58.50, IQR 51.50-67.00) without thyroid pathologies and 30 healthy blood donors (25 female and 5 male; median age 33.50, IQR 27.75-44.25) as controls. Results were obtained by applying molecular virology and immunohistochemistry techniques.

RESULTS

The presence of persistent HHV-6 infection in AIT patients was significantly higher (p 0.0058) than in the control group (44/45 (98%) vs. 23/30 (77%), respectively). Also, a significantly higher frequency of HHV-6 activation marker (U79/80 mRNA) was found in patients' thyroid gland tissue samples with AIT in comparison with the control group (18/44 (41%) vs. 1/17 (6%), respectively; p 0.0118). The median HHV-6 load was found to be higher in patients with active viral infection than in patients without it (2147, IQR 971-4188 vs. 551, IQR 145-1589 copies/1×10⁶ cells; p 0.003). The presence of HHV-6 antigen expression was demonstrated in intrafollicular cellular clusters and immunohistochemistry indicated thyrocytes in the follicle wall.

CONCLUSIONS

These findings provide evidence of strong HHV-6 infection association with AIT development.

Monitoring of human herpesviruses-6 and -7 DNA in saliva samples during the acute and convalescent phases of exanthem subitum

The amounts of the DNAs of human herpesviruses-6 (HHV-6) and -7 (HHV-7) in saliva samples were monitored during the acute and convalescent phases of exanthem subitum (ES) to elucidate the kinetics of virus shedding after ES. A total of 247 saliva samples were collected from 17 children (5 males and 12 females: 8-31 months old at onset). The monitoring period ranged from 152 to 721 days after onset, and in 15 children it was longer than 1 year. Among the 17 cases, 16 were attributed to HHV-6B, while a single case was attributed to HHV-7. Detection rates and average amounts of HHV-6 DNA in saliva samples after ES attributed to HHV-6B were low in the acute phase, increased to the maximum in the convalescent phase at 3-7 months, and then decreased. In addition, to investigate the source of infection, saliva samples from the older siblings (age 3-9 years) and parents of ES patients and children with a history of ES were also examined. The detection rate of HHV-6 DNA in saliva samples from 3- to 9-year-old children was significantly higher than the rate in adult saliva samples. Taken together, these findings suggest that the saliva of children in the convalescent phase of ES might be a more likely source of HHV-6 infection than that of adults. J. Med. Virol. 89:696-702, 2017. © 2016 Wiley Periodicals, Inc.

HHV-6 and seizure: A systematic review and meta-analysis

Human herpesvirus-6 (HHV-6) is a common infection in childhood. This systematic review aims to assess the relationship between HHV-6 infection and seizure disorders based on available literature. MEDLINE database was searched using a search strategy. We included studies that were published after 1993 in English, and described patients with HHV-6 infection and accompanying seizure or status epilepticus. We identified 503 articles, and included 147 studies. Meta-analysis results showed a 0.21 detection rate of HHV-6 in febrile seizure patients. In the febrile seizure group (110 cases), 76 patients had simple and 34 had complex febrile seizures. Patients with "HHV-6 infection and status epilepticus" had a mean age of 16.24 months. In children with febrile illnesses, a higher index of clinical suspicion for HHV-6 infection may be required. Further studies including CSF and brain tissue may be needed to validate relationships between HHV6 infection and epilepsy. J. Med. Virol. 89:161-169, 2017. © 2016 Wiley Periodicals, Inc.

Presence of HHV-6A in Endometrial Epithelial Cells from Women with Primary Unexplained Infertility

To elucidate the roles of human herpesvirus (HHV)-6 primary unexplained infertile women, a prospective randomized study was conducted on a cohort of primary unexplained infertile women and a cohort of control women, with at least one successful pregnancy. HHV-6 DNA was analyzed and the percentage and immune-phenotype of resident endometrial Natural Killer (NK) cells, as the first line of defense towards viral infections, was evaluated in endometrial biopsies. Cytokine levels in uterine flushing samples were analyzed. HHV-6A DNA was found in 43% of endometrial biopsies from primary unexplained infertile women, but not in control women. On the contrary, HHV-6B DNA was absent in endometrial biopsies, but present in PBMCs of both cohorts. Endometrial NK cells presented a different distribution in infertile women with HHV6-A infection compared with infertile women without HHV6-A infection. Notably, we observed a lower percentage of endometrial specific CD56brightCD16- NK cells. We observed an enhanced HHV-6A-specific endometrial NK cell response in HHV-6A positive infertile women, with a marked increase in the number of endometrial NK cells activating towards HHV-6A infected cells. The analysis of uterine flushing samples showed an increase in IL-10 levels and a decrease of IFN-gamma concentrations in infertile women with HHV6-A infection. Our study indicates, for the first time, that HHV-6A infection might be an important factor in female unexplained infertility development, with a possible role in modifying endometrial NK cells immune profile and ability to sustain a successful pregnancy.

The Telomeric Repeats of Human Herpesvirus 6A (HHV-6A) Are Required for Efficient Virus Integration

Human herpesvirus 6A (HHV-6A) and 6B (HHV-6B) are ubiquitous betaherpesviruses that infects humans within the first years of life and establishes latency in various cell types. Both viruses can integrate their genomes into telomeres of host chromosomes in latently infected cells. The molecular mechanism of viral integration remains elusive. Intriguingly, HHV-6A, HHV-6B and several other herpesviruses harbor arrays of telomeric repeats (TMR) identical to human telomere sequences at the ends of their genomes. The HHV-6A and HHV-6B genomes harbor two TMR arrays, the perfect TMR (pTMR) and the imperfect TMR (impTMR). To determine if the TMR are involved in virus integration, we deleted both pTMR and impTMR in the HHV-6A genome. Upon reconstitution, the TMR mutant virus replicated comparable to wild type (wt) virus, indicating that the TMR are not essential for HHV-6A replication. To assess the integration properties of the recombinant viruses, we established an in vitro integration system that allows assessment of integration efficiency and genome maintenance in latently infected cells. Integration of HHV-6A was severely impaired in the absence of the TMR and the virus genome was lost rapidly, suggesting that integration is crucial for the maintenance of the virus genome. Individual deletion of the pTMR and impTMR revealed that the pTMR play the major role in HHV-6A integration, whereas the impTMR only make a minor contribution, allowing us to establish a model for HHV-6A integration. Taken together, our data shows that the HHV-6A TMR are dispensable for virus replication, but are crucial for integration and maintenance of the virus genome in latently infected cells.

Herpesviruses are ubiquitous pathogens that persist in the host for life. Two human herpesviruses (HHV-6A and HHV-6B) can integrate their genetic material into the telomeres of host chromosomes. Integration also occurs in germ cells, resulting in individuals that harbor the virus in every single cells of their body and transmit it to their offspring, a condition that affects about 1% of the human population. We set to elucidate the integration mechanism that allows these viruses to maintain their genome in infected cells. Intriguingly, HHV-6A, HHV-6B and several other herpesviruses harbor telomere sequences at the end of their genome. Removal of these sequences in the genome of HHV-6A revealed that the viral telomeres are crucial for the integration of this human herpesvirus. In addition, we demonstrate that the telomere sequences at the right and left end of the virus genome play different roles in the integration process. Taken together, our data sheds light on the integration mechanism that allows HHV-6A to integrate into somatic cells and to enter into the germ line.

Crystal Structure of Human Herpesvirus 6B Tegument Protein U14

The tegument protein U14 of human herpesvirus 6B (HHV-6B) constitutes the viral virion structure and is essential for viral growth. To define the characteristics and functions of U14, we determined the crystal structure of the N-terminal domain of HHV-6B U14 (U14-NTD) at 1.85 Å resolution. U14-NTD forms an elongated helix-rich fold with a protruding β hairpin. U14-NTD exists as a dimer exhibiting broad electrostatic interactions and a network of hydrogen bonds. This is first report of the crystal structure and dimerization of HHV-6B U14. The surface of the U14-NTD dimer reveals multiple clusters of negatively- and positively-charged residues that coincide with potential functional sites of U14. Three successive residues, L424, E425 and V426, which relate to viral growth, reside on the β hairpin close to the dimer's two-fold axis. The hydrophobic side-chains of L424 and V426 that constitute a part of a hydrophobic patch are solvent-exposed, indicating the possibility that the β hairpin region is a key functional site of HHV-6 U14. Structure-based sequence comparison suggests that U14-NTD corresponds to the core fold conserved among U14 homologs, human herpesvirus 7 U14, and human cytomegalovirus UL25 and UL35, although dimerization appears to be a specific feature of the U14 group.

Human herpesvirus 6B (HHV-6B), a causative agent of exanthema subitum for children and immunocompromised adults, encodes numerous tegument proteins that constitute the viral matrix. HHV-6B U14 is a tegument protein essential for viral propagation, and additionally it interacts with host factors such as tumor suppressor p53 and cellular protein EDD, thereby regulating host cell responses. Here, we report the molecular structure of HHV-6B U14 at an atomic resolution. The N-terminal domain of U14 (U14-NTD) adopts an elongated, helix-rich fold without any significant overall similarity to known structures. U14-NTD forms a 100 kDa homodimer through electrostatic interactions and a wide hydrogen bond network. The U14-NTD homodimer displays four clusters of electrostatic potential with deep grooves, implying multiple binding sites for other viral or host proteins. U14-NTD corresponds to the core fold shared by homologous proteins of human herpesvirus 7 (HHV-7) and of human cytomegalovirus, although dimerization seems to be specific to HHV-6 and HHV-7. The U14-NTD structure provides clues to promote further analysis on the role and behavior of U14 in the pathogenesis of HHV-6. It also leads to a comprehensive understanding of the U14 homologs in beta herpesviruses, and furthermore contributes to the overall knowledge about tegument proteins in herpesviruses.

HHV-8-unrelated primary effusion-like lymphoma associated with clonal loss of inherited chromosomally-integrated human herpesvirus-6A from the telomere of chromosome 19q

Primary effusion lymphomas (PEL) are associated with human herpesvirus-8 (HHV-8) and usually occur in immunocompromised individuals. However, there are numerous reports of HHV-8-unrelated PEL-like lymphomas with unknown aetiology. Here we characterize an HHV-8-unrelated PEL-like lymphoma in an elderly woman who was negative for human immunodeficiency viruses 1 and 2, and hepatitis B and C. The woman was, however, a carrier of an inherited-chromosomally-integrated human herpesvirus-6A (iciHHV-6A) genome in one 19q telomere. The iciHHV-6A genome was complete in blood DNA, encoding a full set of protein-coding genes. Interestingly, the entire iciHHV-6A genome was absent from the HHV-8-unrelated-PEL-like lymphoma cells despite retention of both copies of chromosome 19. The somatic loss of the 19q-iciHHV-6A genome occurred very early during lymphoma development and we propose it occurred via telomere-loop formation and excision to release a circular viral genome that was subsequently lost. Whether release of the HHV-6A genome from the telomere contributed to lymphomagenesis, or was coincidental, remains unclear but this event may have deregulated the expression of HHV-6A or 19q genes or else disrupted telomere function. To establish the frequency and importance of iciHHV-6 loss from telomeres, the HHV-6 copy number should be assessed in tumours that arise in iciHHV-6 carriers.

Co-infections and Pathogenesis of KSHV-Associated Malignancies

Kaposi’s sarcoma-associated herpesvirus (KSHV), also known as human herpes virus 8 (HHV-8) is one of the several carcinogenic viruses that infect humans. KSHV infection has been implicated in the development of Kaposi’s sarcoma (KS), primary effusion lymphoma, and multicentric Castleman’s Disease. While KSHV infection is necessary for the development of KSHV associated malignancies, it is not sufficient to induce tumorigenesis. Evidently, other co-factors are essential for the progression of KSHV induced malignancies. One of the most important co-factors, necessary for the progression of KSHV induced tumors, is immune suppression that frequently arises during co-infection with HIV and also by other immune suppressants. In this mini-review, we discuss the roles of co-infection with HIV and other pathogens on KSHV infection and pathogenesis.

Cytoplasmic tail domain of glycoprotein B is essential for HHV-6 infection

Human herpesvirus 6 (HHV-6) glycoprotein B (gB) is an abundantly expressed viral glycoprotein required for viral entry and cell fusion, and is highly conserved among herpesviruses. The present study examined the function of HHV-6 gB cytoplasmic tail domain (CTD). A gB CTD deletion mutant was constructed which, in contrast to its revertant, could not be reconstituted. Moreover, deletion of gB cytoplasmic tail impaired the intracellular transport of gB protein to the trans-Golgi network (TGN). Taken together, these results suggest that gB CTD is critical for HHV-6 propagation and important for intracellular transportation.

Complete Genome Sequence of Germline Chromosomally Integrated Human Herpesvirus 6A and Analyses Integration Sites Define a New Human Endogenous Virus with Potential to Reactivate as an Emerging Infection

Human herpesvirus-6A and B (HHV-6A, HHV-6B) have recently defined endogenous genomes, resulting from integration into the germline: chromosomally-integrated “CiHHV-6A/B”. These affect approximately 1.0% of human populations, giving potential for virus gene expression in every cell. We previously showed that CiHHV-6A was more divergent than CiHHV-6B by examining four genes in 44 European CiHHV-6A/B cardiac/haematology patients. There was evidence for gene expression/reactivation, implying functional non-defective genomes. To further define the relationship between HHV-6A and CiHHV-6A we used next-generation sequencing to characterize genomes from three CiHHV-6A cardiac patients. Comparisons to known exogenous HHV-6A showed CiHHV-6A genomes formed a separate clade; including all 85 non-interrupted genes and necessary cis-acting signals for reactivation as infectious virus. Greater single nucleotide polymorphism (SNP) density was defined in 16 genes and the direct repeats (DR) terminal regions. Using these SNPs, deep sequencing analyses demonstrated superinfection with exogenous HHV-6A in two of the CiHHV-6A patients with recurrent cardiac disease. Characterisation of the integration sites in twelve patients identified the human chromosome 17p subtelomere as a prevalent site, which had specific repeat structures and phylogenetically related CiHHV-6A coding sequences indicating common ancestral origins. Overall CiHHV-6A genomes were similar, but distinct from known exogenous HHV-6A virus, and have the capacity to reactivate as emerging virus infections.

Detection frequency of human herpesviruses-6A, -6B, and -7 genomic sequences in central nervous system DNA samples from post-mortem individuals with unspecified encephalopathy

In this autopsy-based study, human herpesvirus-6 (HHV-6) and -7 (HHV-7) genomic sequence frequency, HHV-6 variants, HHV-6 load and the expression of HHV-6 antigens in brain samples from the individuals, with and without unspecified encephalopathy (controls), using nested and real-time polymerase chain reactions, restriction endonuclease, and immunohistochemical analysis were examined. GraphPad Prism 6.0 Mann-Whitney nonparametric and chi-square test and Fisher's exact test were used for statistical analysis. The encephalopathy diagnoses were shown by magnetic resonance imaging made during their lifetime and macro- and microscopically studied autopsy tissue materials. Widespread HHV-6 and/or HHV-7 positivity was detected in the brain tissue of various individuals with encephalopathy, as well as in controls (51/57, 89.4 % and 35/51, 68.6 %, respectively; p = 0.009). Significantly higher detection frequency of single HHV-6 and concurrent HHV-6 + HHV-7 DNA was found in pia mater meninges, frontal lobe, temporal lobe, and olfactory tract DNAs in individuals with encephalopathy compared to the control group. HHV-6 load and higher frequency of the viral load >10 copies/10(6) cells significantly differed in samples from individuals with and without encephalopathy. The expression of HHV-6 antigens was revealed in different neural cell types with strong predominance in the encephalopathy group. In all HHV-6-positive autopsy samples of individuals with and without encephalopathy, HHV-6B was revealed. Significantly higher detection frequency of beta-herpesvirus DNA, more often detected HHV-6 load >10 copies/10(6) cells, as well as the expression of HHV-6 antigens in different brain tissue samples from individuals with encephalopathy in comparison with control group indicate on potential involvement of these viruses in encephalopathy development.