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

Tissue and cellular tropism of Eptesicus fuscus gammaherpesvirus in big brown bats, potential role of pulmonary intravascular macrophages

Gammaherpesviruses (γHVs) are recognized as important pathogens in humans but their relationship with other animal hosts, especially wildlife species, is less well characterized. Our objectives were to examine natural Eptesicus fuscus gammaherpesvirus (EfHV) infections in their host, the big brown bat (Eptesicus fuscus), and determine whether infection is associated with disease. In tissue samples from 132 individual big brown bats, EfHV DNA was detected by polymerase chain reaction in 41 bats. Tissues from 59 of these cases, including 17 from bats with detectable EfHV genomes, were analyzed. An EfHV isolate was obtained from one of the cases, and electron micrographs and whole genome sequencing were used to confirm that this was a unique isolate of EfHV. Although several bats exhibited various lesions, we did not establish EfHV infection as a cause. Latent infection, defined as RNAScope probe binding to viral latency-associated nuclear antigen in the absence of viral envelope glycoprotein probe binding, was found within cells of the lymphoid tissues. These cells also had colocalization of the B-cell probe targeting CD20 mRNA. Probe binding for both latency-associated nuclear antigen and a viral glycoprotein was observed in individual cells dispersed throughout the alveolar capillaries of the lung, which had characteristics of pulmonary intravascular macrophages. Cells with a similar distribution in bat lungs expressed major histocompatibility class II, a marker for antigen presenting cells, and the existence of pulmonary intravascular macrophages in bats was confirmed with transmission electron microscopy. The importance of this cell type in γHVs infections warrants further investigation.

The immediate-early protein 1 of human herpesvirus 6B interacts with NBS1 and inhibits ATM signaling

Viral infection often trigger an ATM serine/threonine kinase (ATM)-dependent DNA damage response in host cells that suppresses viral replication. Viruses evolved different strategies to counteract this antiviral surveillance system. Here, we report that human herpesvirus 6B (HHV-6B) infection causes genomic instability by suppressing ATM signaling in host cells. Expression of immediate-early protein 1 (IE1) phenocopies this phenotype and blocks homology-directed double-strand break repair. Mechanistically, IE1 interacts with NBS1, and inhibits ATM signaling through two distinct domains. HHV-6B seems to efficiently inhibit ATM signaling as further depletion of either NBS1 or ATM do not significantly boost viral replication in infected cells. Interestingly, viral integration of HHV-6B into the host's telomeres is not strictly dependent on NBS1, challenging current models where integration occurs through homology-directed repair. Given that spontaneous IE1 expression has been detected in cells of subjects with inherited chromosomally-integrated form of HHV-6B (iciHHV-6B), a condition associated with several health conditions, our results raise the possibility of a link between genomic instability and the development of iciHHV-6-associated diseases.

CD46 isoforms influence the mode of entry by human herpesvirus 6A/B in T cells

CD46 is a receptor for human herpesvirus 6A (HHV-6A) and is in some cells also important for infection with HHV-6B. CD46 has several isoforms of which the most commonly expressed can be distinguished by expression of a BC domain or a C domain in a serine-threonine-proline rich (STP) extracellular region. Using a SupT1 CD46 CRISPR-Cas9 knockout model system reconstituted with specific CD46 isoforms, we demonstrated that HHV-6A infection was more efficient when BC-isoforms were expressed as opposed to C-isoforms, measured by higher levels of intracellular viral transcripts and recovery of more progeny virus. Although the B domain contains several O-glycosylations, mutations of Ser and Thr residues did not prevent infection with HHV-6A. The HHV-6A infection was blocked by inhibitors of clathrin-mediated endocytosis. In contrast, infection with HHV-6B was preferentially promoted by C-isoforms mediating fusion-from-without, and this infection was less affected by inhibitors of clathrin-mediated endocytosis. Taken together, HHV-6A preferred BC isoforms, mediating endocytosis, whereas HHV-6B preferred C isoforms, mediating fusion-from-without. This demonstrates that the STP region of CD46 is important for regulating the mode of infection in SupT1 cells and suggests an epigenetic regulation of the host susceptibility to HHV-6A and HHV-6B infection. Importance CD46 is the receptor used by human herpesvirus 6A (HHV-6A) during infection of T cells, but it is also involved in infection of certain T cells by HHV-6B. The gene for CD46 allows expression of several variants of CD46, known as isoforms, but whether the isoforms matter for infection of T cells is unknown. We used a genetic approach to delete CD46 from T cells and reconstituted them with separate isoforms to study these individually. We expressed the isoforms known as BC and C, which are distinguished by the potential inclusion of a B domain in the CD46 molecule. We demonstrate that HHV-6A prefers the BC isoform to infect T cells, and this occurs predominantly by clathrin-mediated endocytosis. In contrast, HHV-6B prefers the C isoform and infects predominantly by fusion-from-without. Thus, CD46 isoforms may affect susceptibility of T cells to infection with HHV-6A and HHV-6B.

Mapping the Human Herpesvirus 6B transcriptome

The "omics" revolution of recent years has simplified the study of RNA transcripts produced during viral infection and under specific defined conditions. In the quest to find new and differentially expressed transcripts during the course of human Herpesvirus 6B (HHV-6B) infection, we made use of large-scale RNA sequencing to analyze the HHV-6B transcriptome during productive infection of human Molt-3 T-cells. Analyses were performed at different time points following infection and specific inhibitors were used to classify the kinetic class of each open reading frame (ORF) reported in the annotated genome of HHV-6B Z29 strain. The initial search focussed on HHV-6B-specific reads matching new HHV-6B transcripts. Differential expression of new HHV-6B transcripts were observed in all samples analyzed. The presence of many of these new HHV-6B transcripts were confirmed by RT-PCR and Sanger sequencing. Many of these transcripts represented new splice variants of previously reported ORFs, including some transcripts that have yet to be defined. Overall, our work demonstrates the diversity and the complexity of the HHV-6B transcriptome.IMPORTANCERNA sequencing (RNA-seq) is an important tool for studying RNA transcripts, particularly during active viral infection. We made use of RNA-seq to study human Herpesvirus 6B (HHV-6B) infection. Using six different time points, we were able to identify the presence of differentially spliced genes at 6, 9, 12, 24, 48 and 72 hours post-infection. Determination of the RNA profiles in the presence of cycloheximide (CHX) or phosphonoacetic acid (PAA) also permitted identification of the kinetic class of each ORF described in the annotated GenBank file. We also identified new spliced transcripts for certain genes and evaluated their relative expression over time. These data and next-generation sequencing (NGS) of the viral DNA have led us to propose a new version of the HHV-6B Z29 GenBank annotated file, without changing ORF names in order to facilitate trace back and correlate our work with previous studies on HHV-6B.

MicroRNAs of Human Herpesvirus 6A and 6B in Serum and Cerebrospinal Fluid of Multiple Sclerosis Patients

Human herpesvirus-6A (HHV-6A) and −6B (HHV-6B) might be involved in the etiopathogenesis of multiple sclerosis (MS), especially the HHV-6A. We aim at assessing, for the first time in the scientific literature, the HHV-6A/B microRNAs in MS patients. We analyzed the miRNAs of HHV-6A: miR-U86, and −6B: hhv6b-miR-Ro6-1, −2, −3-3p, −3-5p, and −4 in paired samples of serum and CSF of 42 untreated MS patients and 23 patients with other neurological diseases (OND), using Taqman MicroRNA Assays. Intrathecal HHV-6A/B antibody production and anti-HHV-6A/B IgG/IgM levels in serum were measured. MS clinical data were available. We detected the following miRNAs: hhv6b-miR-Ro6-2 (serum: MS:97.7%, OND:95.7%; CSF: MS:81%, OND:86.4%), 3-3p (serum: MS:4.8%, OND:0%; CSF: MS:2.4%, OND:4.5%), −3-5p (serum: MS:95.2%, OND:91.3%; CSF: MS:50%, OND:54.5%), and miR-U86 (serum: MS:54.8%, OND:47.8%; CSF: MS:11.9%, OND:9.1%). In the serum of the whole population (MS and OND patients) we found a significant correlation between the levels of hhv6b-miR-Ro6-2 and −3-5p (Spearman r = 0.839, pcorr = 3E-13), −2 and miR-U86 (Spearman r = 0.578, pcorr = 0.001) and −3-5p and miR-U86 (Spearman r = 0.698, pcorr = 1.34E-5); also in the CSF, between hhv6b-miR-Ro6-2 and −3-5p (Spearman r = 0.626, pcorr = 8.52E-4). These correlations remained statistically significant when both populations were considered separately. The anti-HHV-6A/B IgG levels in CSF and the intrathecal antibody production in positive MS patients for hhv6b-miR-Ro6-3-5p were statistically significant higher than in the negative ones (pcorr = 0.006 and pcorr = 0.036). The prevalence of miR-U86 (30.8%) in the CSF of individuals without gadolinium-enhancing lesions was higher (p = 0.035) than in the ones with these lesions (0%); however, the difference did not withstand Bonferroni correction (pcorr = 0.105). We propose a role of HHV-6A/B miRNAs in the maintenance of the viral latency state. Further investigations are warranted to validate these results and clarify the function of these viral miRNAs.

Equid Herpesvirus 1 Targets the Sensitization and Induction Steps To Inhibit the Type I Interferon Response in Equine Endothelial Cells

Equid herpesvirus 1 (EHV-1) is a viral pathogen of horse populations worldwide spread by the respiratory route and is known for causing outbreaks of neurologic syndromes and abortion storms. Previously, we demonstrated that an EHV-1 strain of the neuropathogenic genotype, T953, downregulates the beta interferon (IFN-β) response in vitro in equine endothelial cells (EECs) at 12 h postinfection (hpi). In the present study, we explored the molecular correlates of this inhibition as clues toward an understanding of the mechanism. Data from our study revealed that EHV-1 infection of EECs significantly reduced both Toll-like receptor 3 (TLR3) and TLR4 mRNA expression at 6 hpi and 12 hpi. While EHV-1 was able to significantly reduce IRF9 mRNA at both 6 hpi and 12 hpi, the virus significantly reduced IFN regulatory factor 7 (IRF7) mRNA only at 12 hpi. EHV-1 did not alter the cellular level of Janus-activated kinase 1 (JAK1) at any time point. However, EHV-1 reduced the cellular level of expression of tyrosine kinase 2 (TYK2) at 12 hpi. Downstream of JAK1-TYK2 signaling, EHV-1 blocked the phosphorylation and activation of signal transducer and activator of transcription 2 (STAT2) when coincubated with exogenous IFN, at 12 hpi, although not at 3 or 6 hpi. Immunofluorescence staining revealed that the virus prevented the nuclear translocation of STAT2 molecules, confirming the virus-mediated inhibition of STAT2 activation. The pattern of suppression of phosphorylation of STAT2 by EHV-1 implicated viral late gene expression. These data help illuminate how EHV-1 strategically inhibits the host innate immune defense by limiting steps required for type I IFN sensitization and induction.IMPORTANCE To date, no commercial vaccine label has a claim to be fully protective against the diseases caused by equid herpesvirus 1 (EHV-1), especially the neurologic form. The interferon (IFN) system, of which type I IFN is of great importance, still remains a viable immunotherapeutic option against EHV-1 infection. The type I IFN system has been exploited successfully to treat other viral infections, such as chronic hepatitis B and C in humans. The current state of research on how EHV-1 interferes with the protective effect of type I IFN has indicated transient induction of type I IFN production followed by a rapid shutdown in vitro in equine endothelial cells (EECs). The significance of our study is the identification of certain steps in the type I IFN signaling pathway targeted for inhibition by EHV-1. Understanding this pathogen-host relationship is essential for the long-term goal of developing effective immunotherapy against EHV-1.

RNA Sequencing of the In Vivo Human Herpesvirus 6B Transcriptome To Identify Targets for Clinical Assays Distinguishing between Latent and Active Infections

Human herpesvirus 6B (HHV-6B) DNA is frequently detected in human samples. Diagnostic assays distinguishing HHV-6B reactivation from latency are limited. This has impaired strategies to diagnose and treat HHV-6B-associated diseases. We used RNA sequencing to characterize and compare the HHV-6B transcriptome in multiple sample types, including (i) whole blood from hematopoietic cell transplant (HCT) recipients with and without HHV-6B plasma viremia, (ii) tumor tissue samples from subjects with large B cell lymphoma infected with HHV-6B, (iii) lymphoblastoid cell lines (LCLs) from subjects with inherited chromosomally integrated HHV-6B or latent infection with HHV-6B, and (iv) HHV-6B Z29 infected SupT1 CD4⁺ T cells. We demonstrated substantial overlap in the HHV-6B transcriptome observed in in vivo and in vitro samples, although there was variability in the breadth and quantity of gene expression across samples. The HHV-6B viral polymerase gene U38 was the only HHV-6B transcript detected in all next-generation RNA sequencing (RNA-seq) data sets and was one of the most highly expressed genes. We developed a novel reverse transcription-PCR assay targeting HHV-6B U38, which identified U38 mRNA in all tested whole-blood samples from patients with concurrent HHV-6B viremia. No HHV-6B U38 transcripts were detected by RNA-seq or reverse transcription-real-time quantitative PCR (RT-qPCR) in whole-blood samples from subjects without HHV-6B plasma detection or from latently infected LCLs. A RT-qPCR assay for HHV-6B U38 may be useful to identify lytic HHV-6B infection in nonplasma samples and samples from individuals with inherited chromosomally integrated HHV-6B. This study also demonstrates the feasibility of transcriptomic analyses for HCT recipients.IMPORTANCE Human herpesvirus 6B (HHV-6B) is a DNA virus that infects most children within the first few years of life. After primary infection, HHV-6B persists as a chronic, latent infection in many cell types. Additionally, HHV-6B can integrate into germ line chromosomes, resulting in individuals with viral DNA in every nucleated cell. Given that PCR to detect viral DNA is the mainstay for diagnosing HHV-6B infection, the characteristics of HHV-6B infection complicate efforts to distinguish between latent and active viral infection, particularly in immunocompromised patients who have frequent HHV-6B reactivation. In this study, we used RNA sequencing to characterize the HHV-6B gene expression profile in multiple sample types, and our findings identified evidence-based targets for diagnostic tests that distinguish between latent and active viral infection.

Cross-sectional analysis of CD8 T cell immunity to human herpesvirus 6B

Human herpesvirus 6 (HHV-6) is prevalent in healthy persons, causes disease in immunosuppressed carriers, and may be involved in autoimmune disease. Cytotoxic CD8 T cells are probably important for effective control of infection. However, the HHV-6-specific CD8 T cell repertoire is largely uncharacterized. Therefore, we undertook a virus-wide analysis of CD8 T cell responses to HHV-6. We used a simple anchor motif-based algorithm (SAMBA) to identify 299 epitope candidates potentially presented by the HLA class I molecule B*08:01. Candidates were found in 77 of 98 unique HHV-6B proteins. From peptide-expanded T cell lines, we obtained CD8 T cell clones against 20 candidates. We tested whether T cell clones recognized HHV-6-infected cells. This was the case for 16 epitopes derived from 12 proteins from all phases of the viral replication cycle. Epitopes were enriched in certain amino acids flanking the peptide. Ex vivo analysis of eight healthy donors with HLA-peptide multimers showed that the strongest responses were directed against an epitope from IE-2, with a median frequency of 0.09% of CD8 T cells. Reconstitution of T cells specific for this and other HHV-6 epitopes was also observed after allogeneic hematopoietic stem cell transplantation. We conclude that HHV-6 induces CD8 T cell responses against multiple antigens of diverse functional classes. Most antigens against which CD8 T cells can be raised are presented by infected cells. Ex vivo multimer staining can directly identify HHV-6-specific T cells. These results will advance development of immune monitoring, adoptive T cell therapy, and vaccines.

This paper deals with the immune response to a very common virus, called human herpesvirus 6 (HHV-6). Most people catch HHV-6 in early childhood, which often leads to a disease known as three-day fever. Later in life, the virus stays in the body, and an active immune response is needed to prevent the virus from multiplying and causing damage. It is suspected that HHV-6 contributes to autoimmune diseases and chronic fatigue. Moreover, patients with severely weakened immune responses, for example after some forms of transplantation, clearly have difficulties controlling HHV-6, which puts them at risk of severe disease and shortens their survival. This can potentially be prevented by giving them HHV-6-specific "killer" CD8 T cells, which are cells of the immune system that destroy body cells harboring the virus. However, little is known so far about such T cells. Here, we describe 16 new structures that CD8 T cells can use to recognize and kill HHV-6-infected cells. We show that very different viral proteins can furnish such structures. We also observe that such T cells are regularly present in healthy people and in transplant patients who control the virus. Our results will help develop therapies of disease due to HHV-6.

Immune responses to an early lytic cytomegalovirus antigen in systemic lupus erythematosus patients: T-cell responses, cytokine secretions and antibody status

We investigated immune responses to a lytic cytomegalovirus antigen (CMVpp52), and to a lytic human herpes virus (HHV) 6 antigen (HHV6p41), in systemic lupus erythematosus (SLE) patients and healthy controls (HCs), in order to clarify if the previously established impaired responses to Epstein-Barr virus (EBV) in SLE patients is a general defect in their responses against (all) HHVs. Multiplex Luminex technology results showed a normal induction of five quantified cytokines (interferon γ, interleukin(IL)12, IL17, IL10, and tumor necrosis factor α) in SLE patients compared to HCs upon stimulation with CMVpp52 and HHV6p41. However, flow cytometric results showed a reduced upregulation of the activation marker CD69 on T-cells from SLE patients (n = 17) compared to HCs (n = 17) upon stimulation with CMVpp52, indicating limited or defective CMVpp52-specific T-cells and/or poor antigen-presentation in SLE patients, and thereby possibly decreased control of the CMV infection. In conclusion, the dysfunctional immune response against EBV previously established in SLE patients does not seem to apply to the same degree regarding the immune responses against CMV or HHV6. Results designate that the main contributing HHV agent in development or exacerbation of SLE (in genetically predisposed individuals) is the previously determined uncontrolled EBV infection, and to a lesser extent CMV infection, and probably with no involvement of HHV6 infection.

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.

Antibodies to early EBV, CMV, and HHV6 antigens in systemic lupus erythematosus patients

OBJECTIVES

We investigated the antibody levels against early antigens of Epstein-Barr virus (EBV), cytomegalovirus (CMV), and human herpesvirus 6 (HHV6) in systemic lupus erythematosus (SLE) patients and healthy controls, and further correlated these antibodies to haematology/biochemistry, serology, and disease activity measures.

METHOD

Immunoglobulin (Ig)M, IgG, and IgA levels against the DNA polymerase processivity factors of EBV, CMV, and HHV6, termed early antigen diffuse (EA/D), pp52, and p41, respectively, were determined in plasma samples from 77 SLE patients and 29 healthy controls by using enzyme-linked immunosorbent assays (ELISAs).

RESULTS

IgM, IgG, and IgA levels against EBV EA/D, and IgG and IgA levels against CMV pp52, were significantly higher in SLE patients compared with healthy controls. Furthermore, EBV EA/D- and CMV pp52-directed IgG levels were inversely and positively associated, respectively, with lymphocyte counts in SLE patients. None of the findings seemed to be associated with use of immunosuppressive medication.

CONCLUSIONS

Our results suggest strong, but opposite, associations of lytic EBV and CMV infections with SLE. The amplified humoral responses to EBV EA/D and CMV pp52 in our SLE patient cohort probably reflect aberrant control of EBV and CMV reactivation. However, reactivation of EBV appeared to correlate with lymphopenic manifestations in SLE patients whereas CMV reactivation seemed to correlate with increments in lymphocyte levels.

Roseolovirus molecular biology: recent advances

Human herpesviruses 6A, 6B, and 7 (HHV-6A, HHV-6B, and HHV-7) are classified within the roseolovirus genus of the betaherpesvirus subfamily. Most humans likely harbor at least two of these large DNA viruses, and 1% of humans harbor germline chromosomally integrated (ci) HHV-6A or HHV-6B genomes. Differences at the genetic level manifest as distinct biologic properties during infection and disease. We provide a brief synopsis of roseolovirus replication and highlight the unique properties of their lifecycle and what is known about the viral gene products that mediate these functions. In the nearly 30 years since their discovery, we have only begun to unlock the molecular strategies these highly evolved pathogens employ to establish and maintain chronic infections in humans.

Human herpesvirus-6B protein U19 contains a p53 BOX I homology motif for HDM2 binding and p53 stabilization

In order to establish a successful infection, it is of crucial importance for invading viruses to alter the activities of the regulatory protein p53. Beta-herpesviruses stabilize p53 and likely direct its activities towards generation of a replication-friendly environment. We here study the mechanisms behind HHV-6B-induced stabilization and inactivation of p53. Stable transgene expression of the HHV-6B protein U19 was sufficient to achieve upregulation of p53. U19 bound directly to the p53-regulating protein HDM2 in vitro, co-precipitated together with HDM2 in lysates, and co-localized with HDM2 in the nucleus when overexpressed. U19 contained a sequence with a putative p53 BOX I-motif for HDM2 binding. Mutation of the two key amino acids within this motif was sufficient to inhibit all the described U19 functions. Our study provides further insight into p53-modulating strategies used by herpesviruses and elucidates a mechanism used by HHV-6B to circumvent the antiviral response.

Inhibition of p53-dependent, but not p53-independent, cell death by U19 protein from human herpesvirus 6B

Infection with human herpesvirus (HHV)-6B alters cell cycle progression and stabilizes tumor suppressor protein p53. In this study, we have analyzed the activity of p53 after stimulation with p53-dependent and -independent DNA damaging agents during HHV-6B infection. Microarray analysis, Western blotting and confocal microscopy demonstrated that HHV-6B-infected cells were resistant to p53-dependent arrest and cell death after γ irradiation in both permissive and non-permissive cell lines. In contrast, HHV-6B-infected cells died normally through p53-independet DNA damage induced by UV radiation. Moreover, we identified a viral protein involved in inhibition of p53 during HHV-6B-infection. The protein product from the U19 ORF was able to inhibit p53-dependent signaling following γ irradiation in a manner similar to that observed during infection. Similar to HHV-6B infection, overexpression of U19 failed to rescue the cells from p53-independent death induced by UV radiation. Hence, infection with HHV-6B specifically blocks DNA damage-induced cell death associated with p53 without inhibiting the p53-independent cell death response. This block in p53 function can in part be ascribed to the activities of the viral U19 protein.

U20 is responsible for human herpesvirus 6B inhibition of tumor necrosis factor receptor-dependent signaling and apoptosis

The immune system targets virus-infected cells by different means. One of the essential antiviral mechanisms is apoptosis induced by ligation of tumor necrosis factor receptor 1 (TNFR1). This receptor can be activated by tumor necrosis factor alpha (TNF-α), which upon binding to TNFR1 induces the assembly of first an inflammatory and later a proapoptotic signaling complex. Here, we report that infection by human herpesvirus 6B (HHV-6B) inhibited poly(ADP-ribose) polymerase (PARP) cleavage, caspase 3 and 8 activation, and IκBα Ser-32 phosphorylation downstream of TNFR1, indicating inhibition of both the inflammatory and apoptotic signaling pathways. We identified a hitherto uncharacterized viral protein, U20, as sufficient for mediating this inhibition. U20 was shown to locate to the cell membrane, and overexpression inhibited PARP cleavage, caspase 3 and 8 activation, IκBα Ser-32 phosphorylation, and NF-κB transcriptional activity. Moreover, small interfering RNA (siRNA) knockdown of U20 demonstrated that the protein is necessary for HHV-6B-mediated inhibition of TNFR signaling during infection. These results suggest an important novel function of U20 as a viral immune evasion protein during HHV-6B infection.

Small RNA deep sequencing identifies microRNAs and other small noncoding RNAs from human herpesvirus 6B

Roseolovirus, or human herpesvirus 6 (HHV-6), is a ubiquitous human pathogen infecting over 95% of the population by the age of 2 years. As with other herpesviruses, reactivation of HHV-6 can present with severe complications in immunocompromised individuals. Recent studies have highlighted the importance of herpesvirus-derived microRNAs (miRNAs) in modulating both cellular and viral gene expression. An initial report which computed the likelihood of various viruses to encode miRNAs did not predict HHV-6 miRNAs. To experimentally screen for small HHV-6-encoded RNAs, we conducted large-scale sequencing of Sup-T-1 cells lytically infected with a laboratory strain of HHV-6B. This revealed an abundant, 60- to 65-nucleotide RNA of unknown function derived from the lytic origin of replication (OriLyt) that gave rise to smaller RNA species of 18 or 19 nucleotides. In addition, we identified four pre-miRNAs whose mature forms accumulated in Argonaute 2. In contrast to the case for other betaherpesviruses, HHV-6B miRNAs are expressed from direct repeat regions (DR(L) and DR(R)) located at either side of the genome. All miRNAs are conserved in the closely related HHV-6A variant, and one of them is a seed ortholog of the human miRNA miR-582-5p. Similar to alphaherpesvirus miRNAs, they are expressed in antisense orientation relative to immediate-early open reading frames (ORFs) and thus have the potential to regulate key viral genes.

Human herpesvirus 6B induces phenotypic maturation without IL-10 and IL-12p70 production in dendritic cells

Human herpesvirus 6B (HHV-6B) is the causative agent of the common childhood febrile illness, exanthema subitum. The virus is predominantly regarded as a T-cell tropic virus, although in reality it has the ability to infect a wide variety of cell types including monocytes, macrophages and dendritic cells (DC). Although DC are important immune regulators, the modulating effects of HHV-6B on DC are controversial. Here, we examine the phenotypic and functional consequences of HHV-6B infection of DC. The addition of HHV-6B to immature DC led to expression of the nuclear viral p41 protein and cell surface expression of the viral glycoprotein gp60/110 consistent with HHV-6B infection. Nevertheless, HHV-6B did not induce noticeable cytopathogenic effects or cell death in infected DC. Importantly, HHV-6B infection induced a partial phenotypic maturation of immature DC as demonstrated by a substantial increase in the expression of HLA-DR, CD86 and CD40, whereas only a minor increase in CD80 and CD83 was observed. This phenotypic maturation was, however, not followed by functional maturation, because HHV-6B infection did not induce IL-10 and IL-12p70 production in immature DC. However, infected DC were still able to react to bacteria-derived stimuli such as lipopolysaccaharide by an even more pronounced production of IL-10 and IL-12p70 when compared to that of uninfected DC.

Whole-genome analysis of pseudorabies virus gene expression by real-time quantitative RT-PCR assay

Background

Pseudorabies virus (PRV), a neurotropic herpesvirus of pigs, serves as an excellent model system with which to investigate the herpesvirus life cycle both in cultured cells and in vivo. Real-time RT-PCR is a very sensitive, accurate and reproducible technique that can be used to detect very small amounts of RNA molecules, and it can therefore be applied for analysis of the expression of herpesvirus genes from the very early period of infection.

Results

In this study, we have developed and applied a quantitative reverse transcriptase-based real-time PCR technique in order to profile transcription from the whole genome of PRV after lytic infection in porcine kidney cells. We calculated the relative expression ratios in a novel way, which allowed us to compare different PRV genes with respect to their expression dynamics, and to divide the PRV genes into distinct kinetic classes. This is the first publication on the whole-genome analysis of the gene expression of an alpha-herpesvirus by qRT2-PCR. We additionally established the kinetic properties of uncharacterized PRV genes and revised or confirmed data on PRV genes earlier examined by traditional methods such as Northern blot analysis. Our investigations revealed that genes with the same expression properties form clusters on the PRV genome: nested overlapping genes belong in the same kinetic class, while most convergent genes belong in different kinetic classes. Further, we detected inverse relationships as concerns the expressions of EP0 and IE180 mRNAs and their antisense partners.

Conclusion

Most (if not all) PRV genes begin to be expressed from the onset of viral expression. No sharp boundary was found between the groups of early and late genes classified on the basis of their requirement for viral DNA synthesis. The expressions of the PRV genes were analyzed, categorized and compared by qRT2-PCR assay, with the average of the minimum cycle threshold used as a control for the calculation of a particular R value. In principle, this new calculation technique is applicable for the analysis of gene expression in all temporally changing genetic systems.

Direct Repeat 6 from human herpesvirus-6B encodes a nuclear protein that forms a complex with the viral DNA processivity factor p41

The SalI-L fragment from human herpesvirus 6A (HHV-6A) encodes a protein DR7 that has been reported to produce fibrosarcomas when injected into nude mice, to transform NIH3T3 cells, and to interact with and inhibit the function of p53. The homologous gene in HHV-6B is dr6. Since p53 is deregulated in both HHV-6A and -6B, we characterized the expression of dr6 mRNA and the localization of the translated protein during HHV-6B infection of HCT116 cells. Expression of mRNA from dr6 was inhibited by cycloheximide and partly by phosphonoacetic acid, a known characteristic of herpesvirus early/late genes. DR6 could be detected as a nuclear protein at 24 hpi and accumulated to high levels at 48 and 72 hpi. DR6 located in dots resembling viral replication compartments. Furthermore, a novel interaction between DR6 and the viral DNA processivity factor, p41, could be detected by confocal microscopy and by co-immunoprecipitation analysis. In contrast, DR6 and p53 were found at distinct subcellular locations. Together, our data imply a novel function of DR6 during HHV-6B replication.

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 induces expression of the human endogenous retrovirus K18-encoded superantigen

BACKGROUND

The superantigen, encoded by the envelope gene (env) of the human endogenous retrovirus (HERV)-K18, may be involved in autoimmunity. Its expression is transactivated in B cells during infection with Epstein-Barr virus and in peripheral blood mononuclear cells (PBMCs) that are treated with IFN-alpha.

OBJECTIVES

We investigated whether HHV-6B infection was able to induce the expression of HERV-K18 env.

STUDY DESIGN

The expression of HERV-K18 env gene was measured by real-time quantitative PCR in HHV-6B-infected PBMC.

RESULTS

Infection of PBMCs with HHV-6B resulted in a rapid and dose-dependent induction of HERV-K18 env gene expression, predominantly in monocytes. Induction was dependent on the interaction of glycoprotein H with CD46, but did not require viral transcription or DNA synthesis. Cycloheximide inhibited both the induction and basal expression of HERV-K18 env, indicating that de novo synthesis of proteins was necessary.

CONCLUSIONS

HHV-6B induced transcriptional activation of the endogenous superantigen HERV-K18 independently of virus replication, which may have consequences for the development of autoimmunity.

Human herpesvirus 6 infections after liver transplantation

Human herpesvirus 6 (HHV-6) infections occur in > 95% of humans. Primary infection, which occurs in early childhood as an asymptomatic illness or manifested clinically as roseola infantum, leads to a state of subclinical viral persistence and latency. Reactivation of latent HHV-6 is common after liver transplantation, possibly induced and facilitated by allograft rejection and immunosuppressive therapy. Since the vast majority of humans harbor the virus in a latent state, HHV-6 infections after liver transplantation are believed to be mostly due to endogenous reactivation or superinfection (reactivation in the transplanted organ). In a minority of cases, however, primary HHV-6 infection may occur when an HHV-6 negative individual receives a liver allograft from an HHV-6 positive donor. The vast majority of documented HHV-6 infections after liver transplantation are asymptomatic. In a minority of cases, HHV-6 has been implicated as a cause of febrile illness with rash and myelosuppression, hepatitis, pneumonitis, and encephalitis after liver transplantation. In addition, HHV-6 has been associated with a variety of indirect effects such as allograft rejection, and increased predisposition and severity of other infections including cytomegalovirus (CMV), hepatitis C virus, and opportunistic fungi. Because of the uncommon nature of the clinical illnesses directly attributed to HHV-6, there is currently no recommended HHV-6-specific approach to prevention. However, ganciclovir and valganciclovir, which are primarily intended for the prevention of CMV disease, are also active against HHV-6 and may prevent its reactivation after transplantation. The treatment of established HHV-6 disease is usually with intravenous ganciclovir, cidofovir, or foscarnet, complemented by reduction in the degree of immunosuppression. This article reviews the current advances in the pathogenesis, clinical diagnosis, and therapeutic modalities against HHV6 in the setting of liver transplantation.

Multicenter comparison of PCR assays for detection of human herpesvirus 6 DNA in serum

Human herpesvirus 6 (HHV-6) is a ubiquitous virus with which infections have been associated with pathologies ranging from delayed bone marrow engraftment to a variety of neurological diseases. The lack of a standardized assay that can be used to detect and estimate HHV-6 DNA contents in various clinical specimens can lead and has led to discordant results among investigators and on the potential association of HHV-6 to diseases. To identify the most reliable and sensitive assays, an identical set of 11 coded serum samples spiked with various quantities of the HHV-6A variant (range, 4 to 400,000 genome copies/ml) was sent to eight independent laboratories around the world. Each laboratory was asked to estimate the HHV-6 DNA content by use of its own protocols and assays. Among the various assays, three TaqMan-based real-time PCR assays yielded quantities that were closest to the quantity of HHV-6 that had been spiked. To provide better homogeneity between the results from the different laboratories working on HHV-6, we propose that investigators interested in quantifying HHV-6 in clinical samples adopt one of these assays.

Restriction of human herpesvirus 6B replication by p53

Human herpesvirus 6B (HHV-6B) induces significant accumulation of p53 in both the nucleus and cytoplasm during infection. Activation of p53 by DNA damage is known to induce either growth arrest or apoptosis; nevertheless, HHV-6B-infected cells are arrested in their cell cycle independently of p53, and only a minor fraction of the infected cells undergoes apoptosis. Using pifithrin-alpha, a p53 inhibitor, and p53-null cells, this study showed that infected epithelial cells accumulated viral transcripts and proteins to a significantly higher degree in the absence of active p53. Moreover, HHV-6B-induced cytopathic effects were greatly enhanced in the absence of p53. This suggests that, in epithelial cells, some of the functions of p53 leading to cell-cycle arrest and apoptosis are restrained by HHV-6B infection, whereas other cellular defences, causing inhibition of virus transcription, are partially retained.

Human herpesvirus 6B induces phosphorylation of p53 in its regulatory domain by a CK2- and p38-independent pathway

Here, we demonstrate that human herpesvirus 6B (HHV-6B) infection upregulates the tumour suppressor p53 and induces phosphorylation of p53 at Ser392. Interestingly, phosphorylation at the equivalent site has previously been shown to correlate with p53 tumour suppression in murine models. Although the signalling pathways leading to Ser392 phosphorylation are poorly understood, they seem to include casein kinase 2 (CK2), double-stranded RNA-activated protein kinase (PKR), p38 or cyclin-dependent kinase 9 (Cdk9). By using column chromatography and in vitro kinase assays, CK2 and p38, but not PKR or Cdk9, eluted in column fractions that phosphorylated p53 at Ser392. However, treatment of cells with neither the CK2 and Cdk9 inhibitor 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole (DRB) nor p38 kinase inhibitors reduced HHV-6B-induced Ser392 phosphorylation significantly. Knockdown of the CK2beta subunit or p38alpha by small interfering RNA had no effect on HHV-6B-induced phosphorylation of p53 at Ser392. Thus, HHV-6B induces p53 Ser392 phosphorylation by an atypical pathway independent of CK2 and p38 kinases, whereas mitogen-activated protein (MAP) kinase signalling pathways are involved in viral replication.

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.

Human herpesvirus 6B inhibits cell proliferation by a p53-independent pathway

BACKGROUND

Various forms of cellular stress can activate the tumour suppressor protein p53, an important regulator of cell cycle arrest, apoptosis, and cellular senescence. Cells infected by human herpesvirus 6B (HHV-6B) accumulate aberrant amounts of p53.

OBJECTIVES

The aim of this study was to investigate the role of p53 accumulation in the HHV-6B-induced cell cycle arrest.

STUDY DESIGN

The role of p53 was studied using the p53 inhibitor pifithrin-a, and cells genetically deficient in functional p53 by homologous recombination.

RESULTS

In response to HHV-6B infection, epithelial cells were arrested in the G1/S phase of the cell cycle concomitant with an aberrant accumulation of p53. However, the known p53-induced mediator of cell cycle arrest, p21, was not upregulated. Approximately 90% of the cells expressed HHV-6B p41, indicative of viral infection. The presence of pifithrin-a, a p53 inhibitor, did not reverse the HHV-6B-induced cell cycle block. In support of this, HHV-6B infection of p53(-/-) cells induced a cell cycle block before S-phase with kinetics similar to or faster than that observed by infection in wt cells.

CONCLUSIONS

HHV-6B infection inhibited host cell proliferation concomitantly with p53 accumulation, but importantly the block in cell cycle occurred by a pathway independent of p53.

Virus-encoded G-protein-coupled receptors: constitutively active (dys)regulators of cell function and their potential as drug target

G-protein-coupled receptors encoded by herpesviruses such as EBV, HCMV and KSHV are very interesting illustrations of the (patho)physiological importance of constitutive GPCR activity. These viral proteins are expressed on the cell surface of infected cells and often constitutively activate a variety of G-proteins. For some virus-encoded GPCRs, the constitutive activity has been shown to occur in vivo, i.e., in infected cells. In this paper, we will review the occurrence of virus-encoded GPCRs and describe their known signaling properties. Moreover, we will also review the efforts, directed towards the discovery of small molecule antagonist, that so far have been mainly focused on the HCMV-encoded GPCR US28. This virus-encoded receptor might be involved in cardiovascular diseases and cancer and seems an interesting target for drug intervention.

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.

Induction of cell-cell fusion from without by human herpesvirus 6B

Human herpesvirus (HHV) 6A induce fusion from without (FFWO), whereas HHV-6B is believed to be ineffective in this process. Here, we demonstrate that HHV-6B induces rapid fusion in both epithelial cells and lymphocytes. The fusion was identified 1 h postinfection, could be inhibited by antibodies to HHV-6B gH and to the cellular receptor CD46, and was dependent on virus titer but independent of de novo protein synthesis and UV inactivation of the virus. Comparisons indicate that HHV-6A is only 10-fold more effective in inducing FFWO than HHV-6B. These data demonstrate that HHV-6B can induce FFWO in epithelial cells and lymphocytes.

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.

Transcription program of red sea bream iridovirus as revealed by DNA microarrays

Red sea bream iridovirus (RSIV) has been identified as the causative agent of a serious disease in red sea bream and at least 30 other marine fish species. We developed a viral DNA microarray containing 92 putative open reading frames of RSIV to monitor the viral gene transcription program over the time course of an in vitro infection and to classify RSIV transcripts into temporal kinetic expression classes. The microarray analysis showed that viral genes commenced expression as early as 3 h postinfection (p.i.) and this was followed by a rapid escalation of gene expression from 8 h p.i. onwards. Based on the expression of some enzymes associated with viral DNA replication, the DNA replication of RSIV appeared to begin at around 8 h p.i. in infected cells in vitro. Using a de novo protein synthesis inhibitor (cycloheximide) and a viral DNA replication inhibitor (phosphonoacetic acid), 87 RSIV transcripts could be classified into three temporal kinetic classes: nine immediate-early (IE), 40 early (E), and 38 late (L) transcripts. The gene expression of RSIV occurred in a temporal kinetic cascade with three stages (IE, E, and L). Although the three classes of transcripts were distributed throughout the RSIV genome, E transcripts appeared to cluster in at least six discrete regions and L transcripts appeared to originate from seven discrete regions. The microarray data were statistically confirmed by using a t test, and were also clustered into groups based on similarity in the gene expression patterns by using a cluster program.

Transcriptional profiling of human herpesvirus type B (HHV-6B) in an adult T cell leukemia cell line as in vitro model for persistent infection

Human herpesvirus 6 (HHV-6), which is present in more than 90% of the human, is known to cause infectious diseases in immuno-compromised patients, e.g., transplant patients. To clarify the possible role of the pattern of expression of HHV-6 genes in various types of HHV-6B infection, we sought to determine whether or not viral DNA microarray could be used for detailed characterization of viral transcription using a HHV-6B DNA microarray that contains 97 known open reading frames of HHV-6B. A subset of genes are preferentially expressed in persistent infection: U16 (IE-B, transactivator, US22 gene family), U18 (IE-B, homolog to HCMV IE glycoprotein), U20 (glycoprotein), U27 (DNA polymerase processivity transactivator), U82 (gL, gH accessory protein), U83 (chemokine), U85 (OX-2 homology, glycoprotein), U90 (IE-A), and U94 (transactivator), respectively. Although the function of each HHV-6B is not fully understood, our study suggests that comprehensive analysis of HHV-6B transcription is useful not only to clarify the pathogenesis of the virus but also to develop new strategies for anti-viral drugs.

Human herpesvirus 6B induces cell cycle arrest concomitant with p53 phosphorylation and accumulation in T cells

We studied the interactions between human herpesvirus 6B (HHV-6B) and its host cell. Productive infections of T-cell lines led to G1/S- and G2/M-phase arrest in the cell cycle concomitant with an increased level and enhanced DNA-binding activity of p53. More than 70% of HHV-6B-infected cells did not bind annexin V, indicating that the majority of cells were not undergoing apoptosis. HHV-6B infection induced Ser20 and Ser15 phosphorylation on p53, and the latter was inhibited by caffeine, an ataxia telangiectasia mutated kinase inhibitor. Thus, a productive HHV-6B infection suppresses T-cell proliferation concomitant with the phosphorylation and accumulation of p53.

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).

Generation and characterization of a monoclonal antibody specific for human herpesvirus 6 variant A immediate-early 2 protein

Two variants (A and B) of human herpesvirus 6 (HHV-6) can be isolated from humans, with each variant having unique biological properties. HHV-6 variant typing is mainly done following amplification of viral genomic DNA followed by restriction endonuclease digestion. Our objective was to generate a monoclonal antibody (mAb) that would allow us to discriminate between variants A and B of HHV-6. BALB/c mice were immunized with a recombinant glutathione-S-transferase protein fused to the immediate-early (IE) 2 protein from HHV-6 variant A. Following splenocytes fusion, one IgG1 kappa light chain mAb (P6H8) was isolated and found to react specifically with variant A IE2 protein in immunofluorescence and western blot assays. The P6H8 antibody represents a useful tool for both fundamental research and clinical applications allowing for the discrimination of infections caused by HHV-6 variants A or B.

A Sensitive Quantification of HHV-6B by Real-time PCR

Human herpesvirus (HHV)-6B is a pathogen causing latent infection in virtually all humans. Nevertheless, the interaction of HHV-6B with its host cells is poorly understood. Although HHV-6B is approximately 90% homologous to HHV-6A, it expresses certain B-specific genes. In order to quantify the amount of expressed viral mRNA we have developed a method using real-time PCR on a LightCycler instrument. Here we describe an assay for the detection of the HHV-6B B6 mRNA, but our approach can easily be extended to involve other mRNAs. This method is useful during the study of HHV-6B biology and offers reliable and reproducible, quantitative detection of viral mRNA below the attomol range.