Temporal mapping of transcripts in herpesvirus 6 variants

Nectin-2 Acts as a Viral Entry Mediated Molecule That Binds to Human Herpesvirus 6B Glycoprotein B

Human herpesvirus 6B (HHV-6B) is a T-lymphotropic virus and the etiological agent of exanthem subitum. HHV-6B is present in a latent or persistent form after primary infection and is produced in the salivary glands or transmitted to this organ. Infected individuals continue to secrete the virus in their saliva, which is thus considered a source for virus transmission. HHV-6B primarily propagates in T cells because its entry receptor, CD134, is mainly expressed by activated T cells. The virus then spreads to the host’s organs, including the salivary glands, nervous system, and liver. However, CD134 expression is not detected in these organs. Therefore, HHV-6B may be entering cells via a currently unidentified cell surface molecule, but the mechanisms for this have not yet been investigated. In this study, we investigated a CD134-independent virus entry mechanism in the parotid-derived cell line HSY. First, we confirmed viral infection in CD134-membrane unanchored HSY cells. We then determined that nectin cell adhesion molecule 2 (nectin-2) mediated virus entry and that HHV-6B-insensitive T-cells transduced with nectin-2 were transformed into virus-permissive cells. We also found that virus entry was significantly reduced in nectin-2 knockout parotid-derived cells. Furthermore, we showed that HHV-6B glycoprotein B (gB) interacted with the nectin-2 V-set domain. The results suggest that nectin-2 acts as an HHV-6B entry-mediated protein.

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.

Cooperative activation of the human herpesvirus 6B U79/80 early gene promoter by immediate-early proteins IE1B and IE2B

The human herpesvirus 6B (HHV-6B) U79/80 gene belongs to the early gene class and appears as early as 3 hr postinfection. It is one of the most abundantly expressed transcripts and a useful diagnostic marker for viral reactivation. However, the expression mechanisms of the U79/80 gene remain unclear. To identify the viral factor(s) that activates the U79/80 promoter along with other HHV-6B core early gene promoters, p41, DNA polymerase, and U41, we examined the activities of U79/80 and other early gene promoters. In HHV-6B-infected MT-4 cells, U79/80 promoter activity was the highest among early gene promoters. In addition, we identified that HHV-6B immediate-early (IE)2B protein is one of the viral proteins involved in the activation of the U79/80 and other early gene promoters. Although the IE2B could independently activate these early gene promoters, the presence of IE1B significantly augmented the activities of early gene promoters. We also found that IE2B bound three human cytomegalovirus IE2-binding consensus, cis repression signal (CRS), within the U79/80 promoter. Moreover, the U79/80 promoter was activated by cellular factors, which are highly expressed in MT-4 cells, instead of HeLa cells because it was upregulated by mock infection and in the absence of IE2B. These results suggested that the activation mechanism of the U79/80 gene differs from other HHV-6B core early genes, apparently supporting its rapid and abundant expression. Therefore, the U79/80 early gene is an actually suitable biomarker of HHV-6B reactivation.

Persistent Roseoloviruses Infection in Adult Patients with Epilepsy

Background: Human herpesviruses (HHV)-6A, HHV-6B and HHV-7 are considered to be involved in the pathogenesis of epilepsy, a common neurological disorder. The objective of this study was to determine the association of roseoloviruses infection with epilepsy. Methods: 53 epilepsy patients and 104 ordinary blood donors were analyzed to determine presence of virus-specific antibodies by enzyme-linked immunosorbent assay (ELISA) and immunofluorescence assay (IFA), genomic sequences, viral load and gene expression by polymerase chain reactions (PCRs) and restriction analysis, HHV-6 protein expression by IFA and level of cytokines by ELISA. Results: Roseoloviruses genomic sequences in DNA samples from whole blood were found in 86.8% of patients versus 54.8% of controls and active infection was revealed only in patients with epilepsy (19.6% of roseolovirus-positive patients). Significantly higher viral load and more frequent gene expression was detected in patients compared to the controls. HHV-6-encoded protein expression was demonstrated in 53.3% of patients with previously detected HHV-6 DNA. Changes in level of cytokines were determined in patients with elevated viral load compared to the patients without elevated viral loads and to the controls. Conclusions: Results on frequent active HHV-6 and HHV-7 infection in epilepsy patient’ peripheral blood indicate on possible involvement of these viruses in the disease development.

DNA Sensors' Signaling in NK Cells During HHV-6A, HHV-6B and HHV-7 Infection

Objectives

The host DNA sensor proteins TLR9, STING, IFI16 are central signaling molecules that control the innate immune response to cytosolic nucleic acids. Here we propose to investigate how Natural killer (NK) cell infection by human herpesvirus (HHV)-6A, HHV-6B or HHV-7 is able to modify DNA sensor signaling in NK cells.

Methods

We infected the NK92 cell line and primary NK cells with cell-free inocula of HHV-6A, HHV-6B or HHV-7 and evaluated TLR9, STING, and IFI16 pathway expression by Real-Time PCR, Western Blot, immunofluorescence and flow cytometry for 1, 2, 3, and 6 days post-infection. We evaluated NK cell cytokine-producing by Real-Time PCR and enzyme immunosorbent assay.

Results

NK92 and primary NK cells were promptly infected by three viruses, as demonstrated by virus presence (DNA) and transcription (RNA) analysis. Our data show STING/STAT6 up-modulation in HHV-6A infected NK cells. NK cells infected with HHV-6B and HHV-7 up-regulated CCL3, IFN-alpha, TNF-alpha, IL-8 and IFN-gamma and slightly induced IL-4, and CCL4. HHV-6A infected NK cells up-regulated IL-4 and IL-13 and slightly induced IL-10, TNF-alpha, IFN-alpha, and IFN-gamma.

Conclusion

For the first time, we demonstrate that HHV-6A, HHV-6B, and HHV-7 infections have a differential impact on intracellular DNA sensors. HHV-6B and HHV-7 mainly lead to the active control of in vivo viral spreading by pro-inflammatory cytokine secretion via TLR9. HHV-6A infected NK cells conversely induced STING/STAT6 pathway, as a mechanism of anti-viral activation, but they were characterized by a Th2 type response and a non-cytotoxic profile, suggesting a potential novel mechanism of HHV-6A-mediated immunosuppression.

Evaluation of liver failure in a pediatric transplant recipient of a liver allograft with inherited chromosomally integrated HHV-6B

BACKGROUND

Active infections of human herpesvirus 6B (HHV-6B) are frequent in immunocompromised recipients after transplantation. Nevertheless, they need to be distinguished from latent inherited chromosomally integrated genomes (iciHHV-6) present in about 1% of the population to avoid unnecessary administration of toxic antivirals.

METHODS

A 5-year-old child presented with acute liver allograft rejection associated with HHV-6 DNA in plasma, which led to an unfavorable outcome. We investigated the possibility of HHV-6 infection derived from an iciHHV-6 present in the donor's liver using molecular and histopathology studies in various tissues, including quantification of HHV-6 DNA, genotyping, sequencing for antiviral resistance genes, relative quantification of viral transcripts, and detection of gB and gH viral proteins.

RESULTS

The presence of iciHHV-6B was evidenced in the donor with signs of reactivation in the gallbladder and transplanted liver (detection of HHV-6B mRNA and late proteins). This localized expression could have played a role in liver rejection. Low viral loads in the recipient's plasma, with identical partial U39 sequences, were in favor of viral DNA released from the transplanted liver rather than a systemic infection.

CONCLUSIONS

Determination of iciHHV-6 status before transplantation should be considered to guide clinical decisions, such as antiviral prophylaxis, viral load monitoring, and antiviral therapy.

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.

Contributions of neurotropic human herpesviruses herpes simplex virus 1 and human herpesvirus 6 to neurodegenerative disease pathology

Human herpesviruses (HVs) have developed ingenious mechanisms that enable them to traverse the defenses of the central nervous system (CNS). The ability of HVs to enter a state of latency, a defining characteristic of this viral family, allows them to persist in the human host indefinitely. As such, HVs represent the most frequently detected pathogens in the brain. Under constant immune pressure, these infections are largely asymptomatic in healthy hosts. However, many neurotropic HVs have been directly connected with CNS pathology in the context of other stressors and genetic risk factors. In this review, we discuss the potential mechanisms by which neurotropic HVs contribute to neurodegenerative disease (NDD) pathology by highlighting two prominent members of the HV family, herpes simplex virus 1 (HSV-1) and human herpesvirus 6 (HHV-6). We (i) introduce the infectious pathways and replicative cycles of HSV-1 and HHV-6 and then (ii) review the clinical evidence supporting associations between these viruses and the NDDs Alzheimer's disease (AD) and multiple sclerosis (MS), respectively. We then (iii) highlight and discuss potential mechanisms by which these viruses exert negative effects on neurons and glia. Finally, we (iv) discuss how these viruses could interact with other disease-modifying factors to contribute to the initiation and/or progression of NDDs.

Cell Culture Systems To Study Human Herpesvirus 6A/B Chromosomal Integration

Human herpesviruses 6A/B (HHV-6A/B) can integrate their viral genomes in the telomeres of human chromosomes. The viral and cellular factors contributing to HHV-6A/B integration remain largely unknown, mostly due to the lack of efficient and reproducible cell culture models to study HHV-6A/B integration. In this study, we characterized the HHV-6A/B integration efficiencies in several human cell lines using two different approaches. First, after a short-term infection (5 h), cells were processed for single-cell cloning and analyzed for chromosomally integrated HHV-6A/B (ciHHV-6A/B). Second, cells were infected with HHV-6A/B and allowed to grow in bulk for 4 weeks or longer and then analyzed for the presence of ciHHV-6. Using quantitative PCR (qPCR), droplet digital PCR, and fluorescent in situ hybridization, we could demonstrate that HHV-6A/B integrated in most human cell lines tested, including telomerase-positive (HeLa, MCF-7, HCT-116, and HEK293T) and telomerase-negative cell lines (U2OS and GM847). Our results also indicate that inhibition of DNA replication, using phosphonoacetic acid, did not affect HHV-6A/B integration. Certain clones harboring ciHHV-6A/B spontaneously express viral genes and proteins. Treatment of cells with phorbol ester or histone deacetylase inhibitors triggered the expression of many viral genes, including U39, U90, and U100, without the production of infectious virus, suggesting that the tested stimuli were not sufficient to trigger full reactivation. In summary, both integration models yielded comparable results and should enable the identification of viral and cellular factors contributing to HHV-6A/B integration and the screening of drugs influencing viral gene expression, as well as the release of infectious HHV-6A/B from the integrated state.IMPORTANCE The analysis and understanding of HHV-6A/B genome integration into host DNA is currently limited due to the lack of reproducible and efficient viral integration systems. In the present study, we describe two quantitative cell culture viral integration systems. These systems can be used to define cellular and viral factors that play a role in HHV-6A/B integration. Furthermore, these systems will allow us to decipher the conditions resulting in virus gene expression and excision of the integrated viral genome resulting in reactivation.

Characterization of human herpesvirus 6A/B U94 as ATPase, helicase, exonuclease and DNA-binding proteins

Human herpesvirus-6A (HHV-6A) and HHV-6B integrate their genomes into the telomeres of human chromosomes, however, the mechanisms leading to integration remain unknown. HHV-6A/B encode a protein that has been proposed to be involved in integration termed U94, an ortholog of adeno-associated virus type 2 (AAV-2) Rep68 integrase. In this report, we addressed whether purified recombinant maltose-binding protein (MBP)-U94 fusion proteins of HHV-6A/B possess biological functions compatible with viral integration. We could demonstrate that MBP-U94 efficiently binds both dsDNA and ssDNA containing telomeric repeats using gel shift assay and surface plasmon resonance. MBP-U94 is also able to hydrolyze adenosine triphosphate (ATP) to ADP, providing the energy for further catalytic activities. In addition, U94 displays a 3′ to 5′ exonuclease activity on dsDNA with a preference for 3′-recessed ends. Once the DNA strand reaches 8–10 nt in length, the enzyme dissociates it from the complementary strand. Lastly, MBP-U94 compromises the integrity of a synthetic telomeric D-loop through exonuclease attack at the 3′ end of the invading strand. The preferential DNA binding of MBP-U94 to telomeric sequences, its ability to hydrolyze ATP and its exonuclease/helicase activities suggest that U94 possesses all functions required for HHV-6A/B chromosomal integration.

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

Shortly after the discovery of human herpesvirus 6 (HHV-6), two distinct variants, HHV-6A and HHV-6B, were identified. In 2012, the International Committee on Taxonomy of Viruses (ICTV) classified HHV-6A and HHV-6B as separate viruses. This review outlines several of the documented epidemiological, biological, and immunological distinctions between HHV-6A and HHV-6B, which support the ICTV classification. The utilization of virus-specific clinical and laboratory assays for distinguishing HHV-6A and HHV-6B is now required for further classification. For clarity in biological and clinical distinctions between HHV-6A and HHV-6B, scientists and physicians are herein urged, where possible, to differentiate carefully between HHV-6A and HHV-6B in all future publications.

Quantification of two viral transcripts by real time PCR to investigate human herpesvirus type 6 active infection

BACKGROUND

Human herpesvirus 6 (HHV-6) causes exanthema subitum and is associated with symptomatic reactivations in immunocompromised patients, particularly after hematopoietic stem cell transplantation. The detection of viral mRNA can help to make the difference between latent, chromosomally integrated and true replicating virus. It can also be a useful tool to investigate viral multiplication in different cell types.

OBJECTIVES

To develop molecular tools for the detection and quantification HHV-6 transcripts that can be used in a clinical setting.

STUDY-DESIGN

Two one-step reverse-transcriptase quantitative real-time PCR (RT-qPCR) were developed for the quantification of the immediate early U90 and the late U100 mRNAs. Viral mRNA loads were compared to viral DNA loads during infection in vitro and in blood samples collected from stem cell transplanted patients.

RESULTS

Analytical performances of the two quantitative real-time PCR were good. In vitro, kinetics of both transcripts was well correlated with DNA levels. Sixty blood samples from patients with active HHV-6 infection were analyzed. Overall agreement of qualitative results for HHV-6 DNA, U90 RNA and U100 RNA was good. HHV-6 DNA loads were significantly higher than mRNA loads. In clinical samples, the amounts of U100 and U90 mRNAs were low and their detection was mainly associated to viral DNA loads upper than 1000 copies/ml of blood.

CONCLUSION

The new assays are sensitive and reliable methods for the monitoring of viral transcription in vitro and in vivo. As their detection is associated to high DNA loads in vivo, they can be helpful tools for the diagnosis of active infection.

Susceptibility of human placenta derived mesenchymal stromal/stem cells to human herpesviruses infection

Fetal membranes (FM) derived mesenchymal stromal/stem cells (MSCs) are higher in number, expansion and differentiation abilities compared with those obtained from adult tissues, including bone marrow. Upon systemic administration, ex vivo expanded FM-MSCs preferentially home to damaged tissues promoting regenerative processes through their unique biological properties. These characteristics together with their immune-privileged nature and immune suppressive activity, a low infection rate and young age of placenta compared to other sources of SCs make FM-MSCs an attractive target for cell-based therapy and a valuable tool in regenerative medicine, currently being evaluated in clinical trials. In the present study we investigated the permissivity of FM-MSCs to all members of the human Herpesviridae family, an issue which is relevant to their purification, propagation, conservation and therapeutic use, as well as to their potential role in the vertical transmission of viral agents to the fetus and to their potential viral vector-mediated genetic modification. We present here evidence that FM-MSCs are fully permissive to infection with Herpes simplex virus 1 and 2 (HSV-1 and HSV-2), Varicella zoster virus (VZV), and Human Cytomegalovirus (HCMV), but not with Epstein-Barr virus (EBV), Human Herpesvirus-6, 7 and 8 (HHV-6, 7, 8) although these viruses are capable of entering FM-MSCs and transient, limited viral gene expression occurs. Our findings therefore strongly suggest that FM-MSCs should be screened for the presence of herpesviruses before xenotransplantation. In addition, they suggest that herpesviruses may be indicated as viral vectors for gene expression in MSCs both in gene therapy applications and in the selective induction of differentiation.

HHV-6 infection of tonsils and adenoids in children with hypertrophy and upper airway recurrent infections

OBJECTIVE

Human herpes virus 6 (HHV-6), the agent of a self-limiting exanthematic disease in childhood, persists in a silent state in the secondary lymphoid organs and the reactivation is characterized by HHV-6-induced inflammatory cytokines. This study investigates the possible etiological role of HHV-6 in children affected by tonsil and adenoid hypertrophy.

METHODS

55 tonsils, 80 adenoids fresh tissues and 74 blood samples were collected from 80 children (mean age 4.8 years, 43.5% female) undergoing elective tonsillectomy and/or adenoidectomy for tissue hypertrophy. Moreover, patients with <5 years old documented upper airway recurrent infections not related to relapsing of acute tonsillitis. Specific IgG antibodies and virus detection (by PCR, variant A/B enzymatic genotyping and real-time PCR) were performed.

RESULTS

In our series, HHV-6 seroprevalence was tested at 50%. HHV-6 variant B was the unique strain finding in 25% of adenoids, in 12.7% of tonsils and in 4% of peripheral blood mononuclear cells (PBMCs). HHV-6-B was prevalent in tonsils of children affected by upper airway infections (17.8% vs 7.4%) while the adenoids represented the more frequent reservoir (30.7% vs 19.5%) in patients with hypertrophy. HHV-6 viral load was low, ranging from 80 to 600 copies/10(6) cells suggesting a latent/persistent phase of infection.

CONCLUSION

These results reinforce the role of the secondary lymphoid organs as an important reservoir for HHV-6B. Nevertheless, infection of lymphoid cells, sustained by a low level of replication, could be sufficient to increase the local injury through an autologous mechanism of inflammation.

Microarray-based determination of the lytic cascade of human herpesvirus 6B

The lytic gene expression of several members of the human herpesvirus family has been profiled by using gene-expression microarrays; however, the lytic cascade of roseoloviruses has not been studied in similar depth. Based on the complete DNA genome sequences of human herpesvirus 6 variant A (HHV-6A) and variant B (HHV-6B), we constructed a cDNA microarray containing DNA probes to their predicted open reading frames, plus 914 human genes. Gene-expression profiling of HHV-6B strain Z29 in SupT1 cells over a 60 h time-course post-infection, together with kinetic classification of the HHV-6B genes in the presence of either cycloheximide or phosphonoacetic acid, allowed the placement of HHV-6B genes into defined kinetic classes. Eighty-nine HHV-6B genes were divided into four different expression kinetic classes: eight immediate-early, 44 early, 33 late and four biphasic. Clustering of genes with similar expression profiles implied a shared function, thus revealing possible roles of previously uncharacterized HHV-6B genes.

Human herpesvirus 6B U19 protein is a PML-regulated transcriptional activator that localizes to nuclear foci in a PML-independent manner

Human herpesvirus 6B (HHV-6B) contains an IE-B domain spanning open reading frames U16/17-U19, based on homology with human cytomegalovirus. Here, the protein product, U19, of the HHV-6B U19 gene is identified as a 47 kDa transcriptional activator. HHV-6B infection or overexpression of U19 transactivated the RANTES promoter. Mutational analysis of the promoter indicated that transactivation was not critically dependent on the promoter sites CRE, NF-kappaB, ISRE or NF-IL6. ND10 are nuclear substructures that are involved in several cellular regulatory pathways, including those controlling gene expression. HHV-6B infection resulted in a reduced number of ND10 structures, but with a concomitantly increased level of promyelocytic leukaemia (PML) protein expression and mRNA induction. The U19 protein co-located to ND10 with PML and heterochromatin protein 1 (HP1), but whilst PML formed a ring structure, U19 also localized to the centre of ND10. Knockdown of PML by small interfering RNA did not prevent U19 localization to ND10-like foci, but instead led to a fourfold increase in U19-induced transcription from the RANTES promoter. Generation of four truncated U19 proteins indicated that the N-terminal portion of the protein contains a sequence responsible for nuclear localization; a domain in the N-terminal half of U19 is responsible for its ND10 localization, whereas the C-terminal portion contains the transactivation domain. None of the truncated proteins retained full transactivating ability on the RANTES promoter. Thus, U19 is a transcriptional activator that co-localizes with PML and localizes to ND10-like foci independently of PML, yet is regulated negatively by PML or its associated proteins.

The simultaneous presence and expression of human hepatitis C virus (HCV), human herpesvirus-6 (HHV-6), and human immunodeficiency virus-1 (HIV-1) in a single human T-cell

We have developed a system that isolates and replicates HCV in vitro. These isolates are called CIMM-HCV. This system has made it possible to analyze the biology, nature, and extent of HCV variability, among other things. Individuals that are infected with HIV-1 are often also infected with HCV and HHV-6. In addition to HCV, our lab has systems for replicating HIV-1 and HHV-6. We asked whether all these viruses could infect the same cells. We report here the successful infection of a T-cell (CEM) by CIMM-HCV, HHV-6, and HIV-1. PCR analyses demonstrated that the CEM cells were productively infected by HHV-6A. RT-PCR showed that the same cell culture was positive for HCV and HIV-1. Co-infection of a T-cell by all three viruses was confirmed by transmission electron microscopy (TEM). All these viruses are highly cytolytic; therefore, triply-infected cells were short lived. However, HIV-1 and HCV co-infected cells unexpectedly lasted for several weeks. Viral replication was unhindered and the phenomenon of 'dominance' was not observed in our experiments. In addition, CIMM-HCV was present in the perinuclear space, suggesting their possible synthesis in the nucleus. This report is based entirely on viruses produced in vitro in our laboratories. As part of the determinations of host ranges of these viruses, studies were designed to demonstrate the infection of a single cell by these viruses and to study the consequences of this phenomenon. All measurements were made on cultured cells and cell culture supernatants.

Co-infection with Mycoplasma pneumoniae and human herpesvirus 6 (HHV-6) in an immunocompetent child with meningoencephalitis: a random association?

Encephalitis can represent a complication of both Mycoplasma and Human Herpesvirus type 6 infections and, although uncommon, is associated with significant morbidity and mortality. We describe a 13-year-old girl with fever, headache and mental changes with a pattern of concomitant Mycoplasma and Human Herpesvirus-6 infection. The hypothetical relationship between this dual infection and the central nervous system disease is discussed.

Human herpesvirus-6 and multiple sclerosis: relapsing-remitting versus secondary progressive

Recently, it has been suggested that human herpesvirus-6 (HHV-6) may play a role in the pathogenesis of relapsing-remitting multiple sclerosis (RRMS), but there is not enough information related to the role of HHV-6 in secondary-progressive MS (SPMS). To address this question, we evaluated HHV-6 prevalence, active viral replication and viral load measured by quantitative real-time PCR, in DNA and mRNA extracted from peripheral blood mononuclear cells (PBMCs) and DNA extracted from serum; the samples were collected from 31 SPMS and 31 RRMS patients in a one-year follow-up study, and sex- and age-matched controls. The results were as follows: i) We found a statistical significant difference in HHV-6 DNA prevalences between RRMS and SPMS patients in: DNA extracted from PBMCs (P= 0.027), DNA extracted from serum (P= 0.010) and mRNA extracted from PBMCs (P =0.010). When we compared HHV-6 prevalences from RRMS patients in relapse and in remission with those from SPMS patients, we only achieved a statistical significance for the relapses (P=0.003 in DNA from PBMCs, and P<0.001 in DNA from serum samples and mRNA from PBMCs). ii) We only found HHV-6 variant A among HHV-6 positive samples in serum. iii) We did not find any difference in HHV-6 viral loads. These results suggest that HHV-6A does not play an active role in SPMS, while this virus may contribute to the pathogenesis of RRMS triggering MS attacks in a subset of patients. Multiple Sclerosis 2007; 13: 578-583. http://msj.sagepub.com

Efficacy of antiviral compounds in human herpesvirus-6-infected glial cells

The beta-herpesvirus human herpesvirus-6 (HHV-6) is becoming increasingly recognized as an important pathogen in immunocompromised patients, particularly in post bone marrow transplant (BMT). Reactivation of latent HHV-6 resulting in encephalitis has been reported in BMT and stem cell transplant (SCT) patients. The development of HHV-6 encephalitis can be a fatal complication, the frequency of which is increasing likely due to improved diagnosis with quantitative polymerase chain reaction (PCR) of cerebrospinal fluid. There are currently no antiviral compounds approved for HHV-6, nor have any controlled clinical trials been conducted. The frequency and severity of HHV-6 encephalitis in both immunocompetent and immunocompromised patients necessitates studies on the usefulness of currently available anti-viral compounds. The authors compared the antiviral efficacy of four drugs currently used for cytomegalovirus (CMV) infection, a beta-herpesvirus sharing homology with HHV-6. In HHV-6A- and HHV-6B-infected T cells, acyclovir, ganciclovir, foscarnet, and cidofovir exhibited antiviral activity consistent with that published in other studies. In HHV-6-infected human astrocytes (U251), however, only foscarnet and cidofovir exhibited antiviral activity and this effect was restricted to infection with HHV-6 variant A. In pathological brain sections from patients with neurological disorders such as multiple sclerosis and epilepsy, HHV-6 has been localized to glial cells. Determination of antiviral activity in human glial fibrillary acidic protein (GFAP)-positive astrocytes of currently used antiviral compounds is essential for potential treatment of HHV-6 and neurological disorders. Our data highlight the necessity for further study of antiviral compound in HHV-6-infected glial cells as well as the development of more selective compounds for HHV-6.

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

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

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.

Long-lasting CD3+ T-cell deficiency after cord blood stem cell transplantation in a human herpesvirus 6-infected child

We report a long-lasting (8-month) reactivation of human herpesvirus 6 (HHV-6) infection in child who had undergone cord blood stem cell transplantation. The reactivation was characterized by high viral loads and by immediate-early mRNA positivity. HHV-6 infection was associated with a deep depletion of CD3, while the CD4/CD8 ratio remained substantially unchanged.

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).

Potent, selective and cell-mediated inhibition of human herpesvirus 6 at an early stage of viral replication by the non-nucleoside compound CMV423

CMV423 (2-chloro-3-pyridin-3-yl-5,6,7,8-tetrahydroindolizine-1-carboxamide) is a new antiviral agent with potent and selective in vitro activity against the beta-herpesvirus human cytomegalovirus (HCMV), but not against alpha- or gamma-herpesviruses. Here we report that its activity also extends to human herpesvirus 6 (HHV-6) and 7 (HHV-7). When compared in vitro to ganciclovir and foscarnet (the standard drugs recommended for treatment of HHV-6 infections), CMV423 showed a superior selectivity, due to its high activity (antiviral IC(50): 53nM) and low cytotoxicity (CC(50): 144microM), both in continuous cell lines and in CBLCs infected with HHV-6. From mechanistic experiments at the level of viral mRNA and protein expression, we learned that CMV423 targets an event following viral entry but preceding viral DNA replication. Its antiviral action was dependent on the cell line used, implying involvement of a cellular component. When compared to a panel of known protein kinase inhibitors, CMV423 was found to share anti-HHV-6 characteristics with herbimycin A, which affects tyrosine kinase activity through heat shock protein 90 (Hsp90) inhibition. We demonstrated that high concentrations of CMV423 have an inhibitory effect on the total cellular protein tyrosine kinase activity, and that CMV423 and herbimycin A, when combined, act synergistically against HHV-6. The activities of cyclin-dependent kinases, protein kinases A and C, and the HHV-6-encoded pU69 kinase were not affected. We, therefore, conclude that CMV423 exerts its activity against HHV-6 through inhibition of a cellular process that is critical at early stages of viral replication and that may affect protein tyrosine kinase activity.

Analysis of human herpesvirus-6 IE1 sequence variation in clinical samples

Herpesvirus immediate early (IE) proteins are known to play key roles in establishing productive infections, regulating reactivation from latency, and creating a cellular environment favourable to viral replication. Human herpesvirus-6 (HHV-6) IE genes have not been studied as intensively as their homologues in the prototype betaherpesvirus human cytomegalovirus (HCMV). Whilst the HCMV IE1 gene is relatively conserved, early studies indicated that HHV-6 IE1 exhibited a high level of sequence variation between HHV-6A and HHV-6B isolates, although the observation was based primarily on virus stocks that had been isolated and propagated in vitro. In this study, we investigated the level of HHV-6 IE1 sequence variation in vivo by direct sequencing of circulating virus in clinical samples without prior in vitro culture. Sequences exactly matching those reported for reference HHV-6 isolates were identified in clinical samples, thus the HHV-6 laboratory strains used in the majority of in vitro studies appear to be representative of virus circulating in vivo with respect to the IE1 gene. The HHV-6 IE1 sequence is also conserved in reference strains that had been passaged extensively in vitro. The high degree of divergence between variant A and B type IE1 sequences was confirmed, but interestingly HHV-6B IE1 sequences were observed to further segregate into two distinct subgroups, with the laboratory strains Z29 and HST representative of these two subgroups. Within each HHV-6B subgroup, a remarkably high level of homology was observed. Thus the HHV-6 IE1 sequence appears highly stable, underlining its potential importance to the viral life cycle.

In vitro and in vivo analysis of human herpesvirus-6 U90 protein expression

In order to establish a reliable method for the detection of human herpesvirus-6 (HHV-6) B antigens in peripheral blood mononuclear cells (PBMCs) collected from HHV-6 infected patients, we created a polyclonal antibody against the HHV-6 B U90 protein (IEA/ex3) and used it to examine the expression of this protein in virus-infected cells and patients' PBMCs. This antibody reacted with 170 and 195 kDa proteins in HHV-6 B-infected cord blood mononuclear cells. The IEA/ex3 antigen was detected in cord blood mononuclear cells at 6 hr post-infection, and the number of infected cells reached its maximum at 48 hr post-infection. The antigen stained in a punctate pattern and partially localized to the promyelocytic leukemia (PML) protein body. We also examined 60 PBMC samples from 60 febrile children (3-19 months old) and detected IEA/ex3 antigen in the PBMCs by laser-scanning microscopy. HHV-6 was isolated from 31 of the 60 samples. The sensitivity and specificity of the antigen detection were 84% (26/31) and 97% (28/29), respectively, in the samples with virus detected. The mean number of antigen-positive PBMCs was 409/10(6) cells in 20 samples with viral isolation. A significant correlation (r = 0.566; P = 0.008) was observed between the viral load and number of antigen-positive cells. Although IEA/ex3 antigen was detected by laser-scanning microscopy in PBMCs (without cultivation) collected from six patients with isolated virus, it was detected in only one sample by conventional fluorescence microscopy. Increasing the intensity by cultivation (24 hr) resulted in a higher detection rate (5/6) even by conventional fluorescence microscopy, which is available in most hospital laboratories.

Human herpesvirus-6 modulates RANTES production in primary human endothelial cell cultures

Human herpesvirus 6 (HHV6) is a beta-herpesvirus capable of infecting several cell types from different origins. HHV6 is the etiological agent of exantem subitum and has been associated with several diseases, all characterized by an inflammatory response triggered by chemokines. We show that strain U1102 of HHV6 is able to infect persistently human endothelial cells obtained from umbilical veins, adult aorta and adult heart microvessels, without apparent cytopathic effect. Analysis by in situ PCR showed that HHV6 sequences were present in 20% of HUVEC, 10% of aortic, and 1% of heart microvascular endothelial cells. Regardless of endothelial cell origin, HHV6 infection induced de novo synthesis of the RANTES CC-chemokine. It was found, however, that microvascular endothelial cells, despite their lower susceptibility to HHV6 infection, showed the highest RANTES expression. Chemokine production occurred also in the absence of viral DNA synthesis. Furthermore, RANTES synthesis required an active viral genome, as UV-inactivated HHV6 infection of endothelial cells did not lead to chemokine production. We investigated the expression of HHV6 U51 gene, which encodes a chemokine receptor that is already known to sequester and down modulate RANTES in epithelial cells. HHV6-infected endothelial cells co-expressed RANTES and U51 mRNAs starting from 12 hr up to 48 hr post-infection. Then, RANTES transcripts disappeared whereas U51 messages continued to be expressed. In conclusion, this study highlights the major role of HHV6 in endothelial cell biology and the development of inflammatory processes.

Interaction of human herpesvirus 6 with human CD34 positive cells

We reported previously that human herpesvirus 6 (HHV-6) suppresses hematopoietic colony formation of erythroid (BFU-E), granulocyte/macrophage (CFU-GM), and megakaryocyte (CFU-Meg) lineages in vitro. Here we describe the interaction between HHV-6 and human CD34+ cells, which are a major source of hematopoietic progenitor cells. CD34+ cells were immunomagnetically isolated from cord blood mononuclear cells using anti-CD34+ antibodies coated onto either Dynabeads trade mark or MACS beads. The CD34+ population selected with Dynabeads showed a broad range of fluorescence. The population selected with MACS beads showed a narrow range of fluorescence. After infection with HHV-6, two transcripts of the immediate early genes were detected with both cell populations. HHV-6 suppressed colony formation of BFU-E, CFU-GM, and CFU-Meg. HHV-6 suppressed cell growth after 3 to 7 days culture in the presence of thrombopoietin (TPO). More differentiated CD34+ cells were more susceptible to the effects of HHV-6. These data indicate that the targets for hematopoietic suppression by HHV-6 are the differentiated cells.

A one-step RT-PCR and a flow cytometry method as two specific tools for direct evaluation of human herpesvirus-6 replication

In order to confirm the occurrence of active Human herpesvirus-6 (HHV-6) infection, two optimal procedures were developed to detect directly replicating virus. MT4 cells and peripheral blood mononuclear cells (PBMCs) infected with two different strains (HST and a patient strain GUI) were used. The first method consisted of a one-step reverse transcription PCR amplifying a part of the late alternatively spliced U100 gene which encode the gp 82-105 viral glycoprotein. Two extraction methods and two RT-PCR kits were evaluated, leading to the selection of TaKaRa mRNA selective PCR kit. The second procedure consisted in a flow cytometry method to analyze the expression of two late viral HHV-6 antigens using 7C7 and 10G6 monoclonal antibodies. Four fixation permeabilization procedures were compared and the preparation of cells with paraformaldehyde (PFA) 4% was found to be optimal. Evaluation of these methods was then realized during a sequential culture of HST strain on MT4 cells. This kinetic study confirmed that Mabs recognized late antigens and demonstrate that the U100 gene splicing starts at a late stage of multiplication whereas unspliced forms are detectable earlier in the cycle.

HHV-6, HHV-7, HHV-8 in gingival biopsies from chronic adult periodontitis patients. A case-control study

BACKGROUND

Recent reports have suggested that various herpesviruses may be involved in the occurrence and progression of different forms of periodontal disease.

OBJECTIVE

The objective of the present study was to investigate the presence of the novel herpesviruses HHV-6, HHV-7 and HHV-8 in gingival biopsies from patients affected by chronic adult periodontitis. As control, gingival biopsies from periodontally healthy subjects were analysed.

MATERIALS AND METHODS

Gingival biopsies were harvested from 23 volunteers: 13 patients affected by chronic adult periodontitis (CAP) and 10 periodontally healthy subjects. Each CAP patient contributed two biopsies involving the epithelium and connective tissue facing the sulcus/periodontal pockets: one biopsy from a site having a probing pocket depth (PPD) > or =5 mm and presenting with bleeding upon probing (affected site) at the time of biopsy collection, and the other biopsy from a site with PPD< or =3 mm and without bleeding on probing (nonaffected site). After DNA extraction, nested PCR was used in herpesvirus identification.

RESULTS

HHV-6 DNA sequences were detected in one non-affected site (8%) and no affected sites (0%) of CAP patients. One biopsy (10%) in healthy subjects revealed HHV-6 positivity. Tissue specimens in 10/13 CAP patients (77%) and 7/10 healthy subjects (70%) contained HHV-7 DNA. HHV-7 prevalence in affected and nonaffected sites of CAP patients was 77% and 54%, respectively. HHV-8 was detected in 7.7% of CAP patients and 0% of healthy subjects.

CONCLUSIONS

Gingival tissue may act as a reservoir for HHV-7. A high prevalence of HHV-7 was detected in both periodontally diseased and healthy individuals. The prevalence of HHV-6 and -8 was similarly low in both groups. Our data do not support an association of investigated herpesvirus species with destructive periodontal disease.

Human herpesvirus 6: molecular biology and clinical features

Human herpesvirus 6 (HHV-6) exists as distinct variants HHV-6A and HHV-6B. The complete genomes of HHV-6A and HHV-6B have been sequenced. HHV-6B contains 97 unique genes. CD46 is the cell receptor for HHV-6, explaining its broad tissue tropism but its restricted host-species range. HHV-6 utilizes a number of strategies to down-regulate the host immune response, including molecular mimicry by production of a functional chemokine and chemokine receptors. Immunosuppression is enhanced by depletion of CD4 T lymphocytes via direct infection of intra-thymic progenitors and by apoptosis induction. Infection is widespread in infants between 6 months and 2 years of age. A minority of infants develop roseola infantum, but undifferentiated febrile illness is more common. Reactivation from latency occurs in immunocompromised hosts. Organ-specific clinical syndromes occasionally result, but indirect effects including interactions with other viruses such as human immunodeficiency virus type 1 and human cytomegalovirus or graft dysfunction in transplant recipients may be more significant complications in this population. Recent advances in quantitative PCR are providing additional insights into the natural history of infection in paediatric populations and immunocompromised hosts.

Split genes and their expression in Kaposi's sarcoma-associated herpesvirus

A split or interrupted gene is defined as a gene consisting of introns and exons. Removal (splicing) of the intron(s) from a primary transcript (pre-mRNA) is essential for creating a mRNA. Initial assignment of a potential protein coding region in the KSHV genome was based on the initiation codon context and predicted protein size larger than 100 amino acids, but the gene discontinuity was disregarded. Experimental investigation of the assigned ORFs has demonstrated that there are up to 25 split genes, more than one fourth of the total KSHV genes described in the KSHV genome. This includes the genes involved in all phases (latent, immediate early, early and late) of KSHV infection. The complexity of a split gene expression depends upon the availability of a proximal promoter and polyadenylation (pA) signal. Sharing a single promoter or a single pA signal by two or three genes is not uncommon in the expression of KSHV split genes and the resulting transcripts are usually polycistronic. Among those of KSHV split genes, 15 genes express a bicistronic or tricistronic RNA and 10 genes express a monocistronic RNA. Alternative RNA splicing could happen in a particular pre-mRNA due to intron or exon inclusion or skipping or the presence of an alternative 5' splice site or 3' splice site. This may, respectively, result in at least 8 species of K8 and 14 species of K15 transcripts. This appears to be related to cell differentiation and stages of the virus infection, presumably involving viral cis elements and trans splicing factors.

A prospective case control study of the association of Gianotti-Crosti syndrome with human herpesvirus 6 and human herpesvirus 7 infections

Gianotti-Crosti syndrome (GCS) is known to be associated with hepatitis B and Epstein-Barr virus (EBV) infections. Apart from a single case report based on serology alone, there are no published data on an association between GCS and human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7) primary infections or reactivations. Our aim was to investigate the association between GCS and HHV-6 and HHV-7 infections. Ten patients diagnosed with GCS at a primary care practice over an 18-month period were recruited. Controls were age- and sex-matched patients with unrelated symptoms requiring venepuncture for other indications. Blood specimens were collected from patients and controls at presentation, and from patients 4 weeks later. Virologic evidence of HHV-6 and HHV-7 infection was sought in peripheral blood leukocytes and plasma using polymerase chain reaction (PCR) for viral DNA, reverse transcriptase polymerase chain reaction (RT-PCR) for HHV-6 U91 mRNA transcripts, and serology. Serology for EBV and hepatitis B virus was done. In contrast to the 10 controls, 2 patients (both infants) with clinically diagnosed GCS had evidence of active HHV-6 infection. This was demonstrated by detection of viral DNA in the absence of antibody in the acute plasma specimens and HHV-6 DNA viral loads of more than 5.3 log10 genome copies/5 microl in the whole blood specimens, a profile previously shown to be diagnostic of recent primary HHV-6 infection. None of the patients had evidence of recent EBV or hepatitis B infection. We conclude that primary HHV-6 infection may be associated with GCS in some infants.

Analysis of the human herpesvirus-6 immediate-early 1 protein

Herpesvirus immediate-early (IE) gene products play key roles in establishing productive infections, regulating reactivation from latency and evading immune recognition. Analyses of HHV-6 IE gene expression have revealed that the IE1 gene of the HHV-6A and HHV-6B variants exhibits a higher degree of sequence variation than other regions of the genome and no obvious similarity to its positional analogue in HCMV. We have analysed expression of the HHV-6 U1102 (HHV-6A) and Z29 (HHV-6B) IE1 gene products using transient expression vectors, stable cell lines and in the context of lytic virus infection. The IE1 transcripts from both variants demonstrate a similar pattern of splice usage within their translated regions. The HHV-6 IE1 proteins from both variants traffic to, and form a stable interaction with, PML-bodies (also known as ND10 or PODS). Remarkably, PML-bodies remained structurally intact and associated with the IE1 protein throughout lytic HHV-6 infection. Immunoprecipitation studies demonstrated that HHV-6 IE1 from both variants is covalently modified by conjugation to the small ubiquitin-like protein SUMO-1. Overexpression of SUMO-1 in cell lines resulted in substantially enhanced levels of IE1 expression; thus sumoylation may bestow stability to the protein. These results indicate that the HHV-6 IE1 protein interacts with PML-bodies yet, unlike other herpesviruses, HHV-6 appears to have no requirement or mechanism to induce PML-body dispersal during lytic replication.

Viral gene expression patterns in human herpesvirus 6B-infected T cells

Herpesvirus gene expression is divided into immediate-early (IE) or alpha genes, early (E) or beta genes, and late (L) or gamma genes on the basis of temporal expression and dependency on other gene products. By using real-time PCR, we have investigated the expression of 35 human herpesvirus 6B (HHV-6B) genes in T cells infected by strain PL-1. Kinetic analysis and dependency on de novo protein synthesis and viral DNA polymerase activity suggest that the HHV-6B genes segregate into six separate kinetic groups. The genes expressed early (groups I and II) and late (groups V and VI) corresponded well with IE and L genes, whereas the intermediate groups III and IV contained E and L genes. Although HHV-6B has characteristics similar to those of other roseoloviruses in its overall gene regulation, we detected three B-variant-specific IE genes. Moreover, genes that were independent of de novo protein synthesis clustered in an area of the viral genome that has the lowest identity to the HHV-6A variant. The organization of IE genes in an area of the genome that differs from that of HHV-6A underscores the distinct differences between HHV-6B and HHV-6A and may provide a basis for further molecular and immunological analyses to elucidate their different biological behaviors.

HHV-6 infects human aortic and heart microvascular endothelial cells, increasing their ability to secrete proinflammatory chemokines

Endothelial cells are important targets for herpesvirus infection. To evaluate the biological effects of human herpesvirus-6 (HHV-6) infection, adult heart microvascular and aortic endothelial cells were examined for in vitro susceptibility to HHV-6 and for the alterations induced by viral infection on the production of monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8). Analysis by reverse transcription-polymerase chain reaction and by in situ polymerase chain reaction showed that HHV-6 replicates in endothelium in the absence of cytopathic effects, and that viral sequences were present in 20% umbilical vein and in 10% aortic and 1% microvascular endothelium. HHV-6 infection upregulated the production of MCP-1 and IL-8, with differences observed between aortic and microvascular endothelium. These findings demonstrate that endothelial cells represent a potential reservoir for HHV-6 infection, and the altered pattern of chemokine production can lead to attraction of immunocompetent cells and to the development of inflammatory processes.

Identification of human herpesvirus 6 latency-associated transcripts

Four kinds of latency-associated transcripts of human herpesvirus 6 were identified which were detected only in latently infected cells. Although they were oriented in the same direction as the immediate-early 1 and 2 (IE1/IE2) genes and shared their protein-coding region with IE1/IE2, their transcription start sites and exon(s) were latency associated.

Development of reverse transcriptase PCR assays for detection of active human herpesvirus 6 infection

We developed reverse transcriptase (RT) PCR assays for the detection of mRNA from three spliced genes of human herpesvirus 6 (HHV-6), the immediate-early genes U16/U17 and U89/U90 and the late gene U60/U66. Sequence analysis determined the splicing sites of these genes. The new assays may be instrumental in investigating the association between HHV-6 and disease.

Characterization of transcripts expressed from human herpesvirus 6A strain GS immediate-early region B U16-U17 open reading frames

Several gene fragments of human herpesvirus 6 (HHV-6) have been shown to activate the human immunodeficiency virus (HIV) type 1 long terminal repeat (LTR). An open reading frame (ORF) designated B701 (Y. Geng, B. Chandran, S. F. Josephs, and C. Wood, J. Virol. 66:1564-1570, 1992), found within a 22-kb HHV-6A strain GS [HHV-6A(GS)] genomic fragment and a 3.8-kb SalI subfragment, was shown to activate the HIV LTR. B701, also known as HHV-6 U16, is located in the immediate-early B (IE-B) region of the genome. The sequence of the 3.8-kb genomic fragment of HHV-6A(GS) is nearly identical to the published sequence of HHV-6A strain U1102, with minor differences. The HHV-6A(GS) B701 ORF (U16) was used to screen an HHV-6A(GS) cDNA library, and two different but overlapping cDNAs were identified. These cDNAs represent differently spliced transcripts ending at different polyadenylation signals. The ORFs included in the cDNAs are positionally homologous to the human cytomegalovirus (HCMV) UL36 ORF. The ORF in one cDNA was generated by splicing together in frame ORFs U17 and U16, and the second cDNA included ORFs U16 and U15. A third differentially spliced cDNA (U16+), was identified by 5' rapid amplification of cDNA ends. The predicted protein was identical to the U16 portion of the U17/U16 spliced gene product but did not include the U17 portion. 5'-extension analyses of the mRNAs demonstrated that at least two potential transcription initiation sites were used to express the transcripts encoding U17 and U16 gene products. Single-stranded U16 and U17 gene-specific RNA probes hybridized with at least five RNA species from infected cells and demonstrated that the expression of these transcripts was differentially regulated. The U17/U16 spliced gene products were expressed at IE times after infection, but a multiply spliced gene product encoded by U16 was expressed as a late gene. The U17/U16 and the U16+ gene products transactivated the HIV LTR. Thus, while there are similarities to the HCMV UL36-UL38 gene family, some of the IE-B U17/U16 transcripts are unique to HHV-6.

Expression of human herpesvirus 6B rep within infected cells and binding of its gene product to the TATA-binding protein in vitro and in vivo

We have characterized the human herpesvirus 6B (HHV-6B) rep gene, which is a homologue of the adeno-associated virus type 2 rep and is unique in the herpesvirus family. Three transcripts, 9.0, 5.0, and 2. 7 kb (the major transcript), were detected by Northern blotting using an HHV-6B rep probe under late conditions. We investigated the expression kinetics of the rep gene using cycloheximide (CHX) and phosphonoformic acid (PFA), which are inhibitors of protein synthesis and viral DNA synthesis, respectively. The 5.2-kb transcript was mainly detected in the absence of protein biosynthesis upon infection, and none of the 9.0-, 5.0-, and 2.7-kb transcripts detected under the late conditions were detected in the presence of CHX and PFA. Sequences obtained from a cDNA library showed that the 5.0- and 2.7-kb transcripts were spliced from two and three exons, respectively, and the 2.7-kb transcript was more abundant. Immunohistochemistry using an antibody raised against the HHV-6 rep gene product (REP) revealed that REP was mainly present in the nucleus of MT-4 cells within 24 h after infection with HHV-6B. Using pull-down assays, coimmunoprecipitation, and a mammalian two hybrid system, we showed that HHV-6 REP binds to a transcription factor, human TATA-binding protein, through its N-terminal region.

Human herpesvirus-6 and -7 infections in children: agents of roseola and other syndromes

Human herpesvirus-6 (HHV-6) and -7 (HHV-7) infections typically are silent or manifested as mild febrile illnesses including classic roseola. In addition, case reports and epidemiologic data support the rare occurrence of HHV-6 encephalitis in immunocompromised as well as immunocompetent subjects. Although many other diseases have been putatively associated with HHV-6 or HHV-7, these associations are not well documented due to small numbers, use of tests incapable of distinguishing latent from replicating virus, potential virus cross-reactivity, or contradictory results. Further careful studies are needed to confirm these disease associations. Laboratory tests for diagnosing active HHV-6 and HHV-7 infections include virus culture, antigen detection, and polymerase chain reaction of cell-free biologic fluid. Although HHV-6 and HHV-7 are inhibited by several antiviral drugs in the laboratory, including ganciclovir and foscarnet, no clinical trials have assessed their benefit. Nevertheless, treatment may be considered for patients with serious HHV-6- or HHV-7-associated disease confirmed with accurate virologic tests.

Human herpesvirus 6

Human herpesvirus 6 (HHV-6), a member of the beta-herpesvirinae subfamily, is highly seroprevalent, has a worldwide distribution, and infection usually occurs within the first two years of life. In this age group, HHV-6 causes febrile illness including exanthem subitum with seizures a recognised complication. The virus is predominantly T lymphotropic although it can infect a variety of cell types in vitro and CD46 has recently been identified as a cellular receptor. The virus persists in the host, with a latent state proposed in monocytes and bone marrow progenitor cells, and chronic infection in salivary glands. The virus is pathogenic in the post transplantation period and may be a cofactor in the progression of HIV disease. The virus has also been associated with multiple sclerosis (MS), with the virus detected in oligodendrocytes particularly in plaque regions. The role of HHV-6 in MS remains controversial and a more extensive understanding of its neurotropism and association with disease is required. Two variants of HHV-6 exist (A and B) and comparison of their complete nucleotide sequences shows the genomes to be colinear, with a high degree of homology. Variation in specific regions of the genome is more extensive and probably accounts for biological and pathological differences. Almost exclusively, variant B is associated with febrile illness in childhood and is the predominant variant detected in healthy individuals. The epidemiology of HHV-6A infection needs to be better defined, although it is significantly less prevalent. Biological, genetic, epidemiological and pathological findings suggest that the two variants are divergent.

U94, the human herpesvirus 6 homolog of the parvovirus nonstructural gene, is highly conserved among isolates and is expressed at low mRNA levels as a spliced transcript

Human herpesvirus 6 variants A and B (HHV-6A and HHV-6B, respectively) encode homologs (U94) of the parvovirus nonstructural gene, ns1 or rep. Here we describe the HHV-6B homolog and analyze its genetic heterogeneity and transcription. U94 nucleotide and amino acid sequences differ by approximately 3.5% and 2.5%, respectively, between HHV-6A and HHV-6B. Among a collection of 17 clinically and geographically disparate HHV-6 isolates, intravariant nucleotide and amino acid sequence divergence was less than 0.6% and 0.2%, respectively; all 13 HHV-6B isolates had identical amino acid sequences. The U94 transcript is spliced to remove a 2.6-kb intron and is expressed at very low levels relative to other HHV-6B genes, reaching approximately 10 copies per cell 3 days after infection. The mRNA has several small AUG-initiated open reading frames upstream of the U94 open reading frame, a hallmark of proteins expressed at low levels. Consistent with this, the U94-encoded protein was immunologically undetectable in HHV-6B-infected cells. The high degree of sequence conservation suggests that the gene function is nearly intolerant of sequence variation. The low abundance of U94 transcripts and the presence of encoded inefficient translation initiation suggest that the U94 protein may be required only in small amounts during infection.

Detection of human herpesvirus 6 by reverse transcription-PCR

The role of human herpesvirus 6 (HHV-6) in disease beyond primary infection remains unclear. We have developed and validated a new reverse transcription-PCR (RT-PCR) assay for HHV-6 that can determine the presence of HHV-6 in clinical specimens and differentiate between latent and replicating virus. Peripheral blood mononuclear cells from 109 children were evaluated for HHV-6 by RT-PCR, DNA PCR, and viral culture. Of these samples, 106 were suitable for analysis. A total of 20 samples were positive for HHV-6 by culture and DNA PCR, of which 19 were positive by RT-PCR (sensitivity, 95%). All 28 samples from children that were negative by viral culture, but positive by DNA PCR, were negative for viral transcripts by our RT-PCR assay. One positive RT-PCR result was observed in 56 samples that were negative by tissue culture and DNA PCR. This indicates a low rate of false-positive results (1.2%) and a specificity of 98.8%. This RT-PCR assay can reliably differentiate between latent and actively replicating HHV-6 and should allow insight into the pathogenesis of this ubiquitous virus.