Antigenic and genetic differentiation of the two putative types of human herpes virus 6

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.

Selective Activity of Various Nucleoside and Nucleotide Analogues against Human Herpesvirus 6 and 7

We have developed a new sensitive enzyme immunoassay (EIA) and MTT (tetrazolium salt) assay for screening compounds against two variants of human herpesvirus 6 (HHV-6A, HHV-6B) and human herpesvirus 7 (HHV-7) and evaluated the anti-HHV-6 and HHV-7 activity of a series of anti-herpesvirus compounds and acyclic nucleoside phosphonate analogues. The results indicate that the pattern of activity of these compounds against these betaherpesviruses is similar to that for human cytomegalovirus (HCMV). The highest potency and selectivity against the two variants of HHV-6 and HHV-7 was demonstrated by S2242 (N7-isomer of 6-deoxy-ganciclovir). Also, ganciclovir (GCV), foscarnet, (phosphonoformic acid; PFA) and the acyclic nucleoside phosphonate analogues such as cidofovir (HPMPC) exhibited selective inhibitory activity against these viruses. Thymidine kinase (TK)-dependent drugs (acyclovir, ACV; brivudin, BVDU; and sorivudine, BVaraU) showed little, if any, activity. These results suggest a structural homology of the DNA polymerase and a lack of TK gene among these three betaherpesviruses (HHV-6, HHV-7 and HCMV). The finding that HHV-7 was highly sensitive to GCV also suggests that HHV-7 may have an HCMV-UL97-homologue gene for the phosphorylation of GCV. The present EIA method is more rapid and sensitive than the previously reported procedures and could be useful for the large-scale screening of compounds against HHV-6 and HHV-7.

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.

Development of a microwell adapted immunoblot system with recombinant antigens for distinguishing human herpesvirus (HHV)6A and HHV6B and detection of human cytomegalovirus

BACKGROUND

The human cytomegalovirus (HCMV) and the human herpesvirus 6 (HHV6) are widely distributed in the human population. The variants A and B of HHV6 are closely related to each other and cannot be distinguished by common serological methods like enzyme-linked immunosorbent assay (ELISA) or immunofluorescence test (IFT). The aim of this study was to develop a microwell-adapted blot system for specificity detection of human cytomegalovirus and human herpesvirus 6A and 6B (HHV6A, HHV6B) that combines the advantages of ELISA (automation and multiplex detection) and immunoblotting (antigen-specific antibody detection with high specificity).

METHODS

Ten HCMV, five HHV6A and five HHV6B antigens were expressed as fusion proteins and tested with sera of children (n=30), of healthy young adults (n=30) and of older adults (n=30) in a newly developed microblot system.

RESULTS

Sensitivity and specificity of HCMV and HHV6 microblots were comparable to commercially available[ELISA, IFT and to line assay tests. The advantage of the HHV6 microblot is the possibility of distinguishing between HHV6A-monovalent sera, HHV6B-monovalent sera and HHV6A/B-polyvalent sera. Most sera of children younger than 2 years showed only HHV6B antigen positivity, while most sera of adults and children aged over 2 years reacted with HHV6A and B proteins, although predominance for HHV6B was observed.

CONCLUSIONS

The authors were able to detect HCMV positive sera and to distinguish between HHV6A-monovalent sera, HHV6B-monovalent sera and HHVA/B-polyvalent sera with the new developed microblot system. Predominance of HHV6B was observed in sera of children and adults.

Length variability of telomeric repeat sequences of human herpesvirus 6 DNA

The telomeric repeat sequences (TRS) located near both ends of human herpesvirus 6 (HHV-6) genome are unique structures of unknown function among human herpesviruses. The goal of the present study was to investigate the variability of TRS copy number among different laboratory strains and HHV-6-infected clinical specimens regarding the two variants A and B of HHV-6. DNA obtained from infected cells was submitted to a PCR assay designed to amplify the part of genome containing TRS specifically either for HHV-6A or HHV-6B. Amplicons were analyzed by electrophoresis on agarose gel with ethidium bromide staining and nucleotide sequencing. The number of TRS copies was highly variable among the distinct laboratory strains and clinical specimens studied, ranging from 15 up to more than 180. However, this number was constant for a given strain after serial propagation in cell cultures as well as in different samples from the same subject. This permitted to detect a mixed infection with two distinct strains of HHV-6A within the same patient. The PCR-based analysis of HHV-6 TRS has a limited sensitivity but is highly specific, which provides the opportunity to include it in the set of molecular tools dedicated to the study of HHV-6 epidemiology.

Variability of gB and gH genes of human herpesvirus-6 among clinical specimens

The isolates of human herpesvirus-6 (HHV-6), a betaherpesvirus closely related to human cytomegalovirus (HCMV), are classified as either variants A (HHV-6A) or B (HHV-6B) but their intravariant variability has not been studied extensively so far. The full-length genes of envelope glycoproteins gB and gH from 40 distinct HHV-6-DNA-positive specimens and 11 laboratory strains were amplified using PCR, and their nucleotide sequence determined. Nucleotide divergences were observed at 156 (6.2%) and 98 (4.7%) positions in the case of gB and gH genes respectively. Phylogenetic analysis, including reference strain sequences, confirmed the unambiguous distinction between HHV-6A and HHV-6B for both genes. In the case of HHV-6B isolates, two subgroups of gB gene (designated as gB-B1 and gB-B2) and two subgroups of gH gene (gH-B1 and gH-B2) were identified but the phylogenetic trees of both genes were not fully congruent with each other. The analysis of gB and gH protein sequences showed that 26 and 39 critical amino acid changes respectively permitted the unambiguous distinction between HHV-6A and HHV-6B. Among HHV-6B isolates, gB and gH gene subgroups were characterized by specific amino acid signatures made of six, and two residues respectively. The linkage unbalance between amino acid signatures as well as the distribution of crucial nucleotide changes strongly suggested the occurrence of intravariant recombination within gB gene among HHV-6B isolates. These results indicate that, as in the case of HCMV, homologous recombination may contribute to the genetic variability of HHV-6.

Persistent long-term human herpesvirus 6 (HHV-6) infection in a patient with langerhans cell histiocytosis

Langerhans cell histiocytosis (eosinophilic granuloma) was first diagnosed in the adolescence of a male patient presented. Several years later persisting human herpesvirus 6 (HHV-6) infection was recognized. The HHV-6 infection could be verified retrospectively in his historical histological samples; the continuous presence of HHV-6 could be established through 17 years of disease course. The patient was operated several times during this period for painful relapses, and developed diabetes insipidus. At variable time points during the clinical course, Varicella zoster (VZV), Epstein-Barr virus (EBV) and human herpesvirus 8 (HHV-8) infections were temporarily detected from blood samples and biopsy specimens. HHV-6 was the only virus continuously identified throughout the entire follow-up period. Antiviral therapy effectively cleared EBV and HHV-8, but HHV-6 remained detectable throughout the disease course. Since DNA sequences of HHV-6 could be detected in the pathologic histiocytes of eosinophilic granuloma, and from other samples taken later on, it is suggested that long-term HHV-6 infection may be associated with development or progression of Langerhans cell histiocytosis.

Detection of four lymphotropic herpesviruses in Hungarian Patients with multiple myeloma and lymphoma

It has been suggested that human herpesvirus 8 (HHV-8), also known as KSHV (Kaposi's sarcoma-associated human herpesvirus), might possess a promoting effect in the development and progression of monoclonal gammopathies. In this study, the presence of Epstein-Barr virus (EBV), human cytomegalovirus (CMV), human herpesvirus 6 (HHV-6) and human herpesvirus 8 (HHV-8) were tested in patients with multiple myeloma (MM) using both serologic and nucleic acid amplification techniques. The transient reactivation or continuous presence of EBV, CMV, HHV-6 and HHV-8 could be detected in, respectively, 36, eight, 13 and 29 of 69 MM patients; nine, one, four and six of 16 monoclonal gammopathy of unknown significance patients; and seven, four, zero and five of 10 Waldenström's macroglobulinemia patients. The total number of MM patients was 95. HHV-8 PCR-positivity was significantly more frequent in the MM group than in the control group of patients with non-Hodgkin's lymphoma (NHL). However, serologic testing did not reveal significant differences between the two patient groups. The number of MM patients with concomitant herpesvirus infections as detected by PCR was as follows: 15 double, seven triple and two quadruple virus nucleic acid positive. In 13/95 MM patients, the simultaneous presence of acute EBV infection and HHV-8 PCR-positivity was detected compared with none of the control group (P=0.009). These results indicate that in addition to HHV-8, the transitional reactivation of EBV may also play a role in the pathogenesis of MM.

Human herpesvirus 6 (HHV6) infection

Human herpes virus-6 was first reported in 1986 and is the sixth member of the herpes virus family. HHV-6 consists of two closely related variants HHV-6A and HHV-6B. The majority of infections occur in healthy infants with most infections caused by HHV-6B. The virus preferentially infects CD4+T-lymphocytes and the surface marker CD46 acts as a co-receptor. Infection is followed by persistence and latency in different cells and organs including monocytes/macrophages, salivary glands, the brain and the kidneys. In this article we will discuss the clinical manifestations of HHV-6 infection in healthy children and the syndromes associated with HHV-6 reactivation in immunocompromised patients. Evidence of association between HHV-6 infection and different clinical entities such as multiple sclerosis, malignancy, infectious momononucleosis, drug hypersensitivity syndromes and skin eruptions is discussed. Published data on the use and efficacy of antiviral agents in complicated infections and infections in immunocompromised patients is presented.

Fatal myocarditis associated with acute parvovirus B19 and human herpesvirus 6 coinfection

We report on the case of a healthy young boy who developed a fulminant myocarditis due to acute coinfection with erythrovirus (parvovirus B19) and human herpesvirus 6 (HHV-6) in the absence of an antiviral immune response. We suggest that the HHV-6-induced immunosuppression enhanced dissemination of parvovirus B19, which led to fatal myocarditis.

Flow cytometric evaluation of antiviral agents against human herpesvirus 6

Antiviral activities of acyclovir (9-[(2-hydroxyethoxy) methyl] guanine, ACV), penciclovir (9-[4-hydroxy-3-(hydroxymethyl) butyl] guanine, PCV), ganciclovir ([9-(1,3-dihydroxy-2-propoxy) methyl] guanine, GCV), and foscarnet (phosphonoformic acid, PFA) were determined against Human Herpesvirus 6 (HHV-6) by flow cytometric technique. The technique is based on the detection of gp116 antigen expression in virus infected cells. Susceptibility was defined in terms of drug concentration which reduced the number of cells expressing HHV-6 gp116 antigen with a mean fluorescent intensity (MFI) by 50% as compared to virus infected untreated cells. GCV was found to be most effective against HHV-6 followed by PFA, PCV and ACV. For HHV-6A, the mean 50% inhibitory concentrations (IC50) of GCV and PFA were found to be 3.4 microM and 34.7 microM respectively, whereas the IC50 of ACV and PCV were found to be 53.7 microM and 37.9 microM respectively. For HHV-6B, the IC50 of GCV and PFA were found to be 5.7 microM and 71.4 microM respectively, whereas the IC50 of ACV and PCV were found to be 119.0 microM and 77.8 microM respectively. Flow cytometry is a valuable technique for the evaluation of antiviral compounds against viruses including HHV-6.

Quantitation of human herpesvirus 6 DNA in infant with exanthem subitum by microplate PCR-hybridization assay

BACKGROUND

Quantitative analysis of human herpesvirus 6 (HHV-6) genome is important for monitoring active virus infection. The purpose of our study is to evaluate the reliability of a hybridization-based microtiter plate assay (polymerase chain reaction enzyme-linked immunosorbent assay (PCR ELISA)) for quantifying the virus genome.

METHODS

Semiquantitative analysis of the virus genome was carried out in 31 (18 male and 13 female) infants with primary HHV-6 infection. If the HHV-6 virus could be isolated from the peripheral blood mononuclear cells (PBMC), the infants were defined as being infected with HHV-6. The PCR ELISA method was used to determine the virus load. A titration of the virus was also carried out in the samples obtained during the acute phase of exanthem subitum.

RESULTS

Specificity of the method was demonstrated by a lack of amplification of human herpesvirus 7 and cytomegalovirus DNA. The upper and lower detection limits of the method were 58 and 5800 copies of the virus genome, respectively. The quantity of HHV-6 DNA in the PBMC during the acute phase (879 +/- 975 copies/10(4) PBMC) was significantly higher than during the convalescent phase (54 +/- 76 copies/10(4) PBMC). Furthermore, the virus load in acute phase plasma (53 +/- 75 copies/microL) was also significantly higher than in the convalescent phase samples (2 +/- 9 copies/microL). Virus load in both PBMC and plasma gradually increased after the onset of exanthem subitum until about day 3 to 4 of the illness, but then decreased quickly. However, there was no significant association between virus load and the numbers of infected cells.

CONCLUSION

Virus load in both PBMC and plasma gradually increased after the onset of exanthem subitum until about day 3 and day 4 of the illness, respectively, then it decreased quickly. These results indicate that our PCR ELISA system is reliable for monitoring active HHV-6 infection in vivo.

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

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

Comparison of the complete DNA sequences of human herpesvirus 6 variants A and B

Human herpesvirus 6 (HHV-6), which belongs to the betaherpesvirus subfamily and infects mainly T cells in vitro, causes acute and latent infections. Two variants of HHV-6 have been distinguished on the basis of differences in several properties. We have determined the complete DNA sequence of HHV-6 variant B (HHV-6B) strain HST, the causative agent of exanthem subitum, and compared the sequence with that of variant A strain U1102. A total of 115 potential open reading frames (ORFs) were identified within the 161,573-bp contiguous sequence of the entire HHV-6 genome, including some genes with remarkable differences in amino acid identity. All genes with <70% identity between the two variants were found to contain deleted regions when ORFs that could not be expressed were excluded from the comparison. Except in the case of U47, these differences were found in immediate-early/regulatory genes, DR2, DR7, U86/90, U89/90, and U95, which may represent characteristic differences of variants A and B. Also, we have successfully typed 14 different strains belonging to variant A or B by PCR using variant-specific primers; the results suggest that the remarkable differences observed were conserved evolutionarily as variant-specific divergence.

Human herpesvirus 6 open reading frame U83 encodes a functional chemokine

Some viruses including herpesviruses have undergone evolution to benefit viral infection and propagation by pirating and modifying host genes such as chemokine genes. Human herpesvirus 6 (HHV-6), acutely or persistently infects mononuclear cells in vitro. DNA sequence analysis of HHV-6 has revealed that the putative protein encoded by an open reading frame (ORF) of the U83 gene in HHV-6 variant B resembled a human chemokine. We have cloned the U83 gene and analyzed the biological function of this gene. The U83 gene contained an ORF encoding a 113-amino-acid peptide, starting at the first methionine and containing a possible signal peptide and the typical cysteine residues characteristic of the chemokines. Reverse transcription-PCR analysis of mRNA and immunofluorescent-antibody testing of infected cells both indicated that the encoded protein was a late protein. The ORF U83 gene fused to the Fc gene was expressed as a fusion protein in COS-7 cells by transfection, and the fusion protein was purified from the supernatant of transfected cells to test its biological function. The purified protein was capable of inducing transient calcium mobilization in THP-1 cells and of chemotactically activating THP-1 cells. These findings suggested that the U83 protein might play an important role in HHV-6 propagation in vivo by activating and trafficking mononuclear cells to sites of viral replication, thus aiding the development of superbly efficient virus production mechanisms.

Selection and characterization of two specific monoclonal antibodies directed against the two variants of human herpesvirus-6

Monoclonal antibodies (mAbs) specific for human herpesvirus-6 (HHV6) proteins were derived from the splenocytes of mice immunized with HHV6 TAN isolate-infected peripheral blood mononuclear cells. The two mAbs 8C8 and 7C7 reacted by means of immunofluorescence and immunoperoxidase assays with both variant A and variant B isolates giving two different staining patterns. In infected cells, cytoplasmic diffuse staining was observed with mAb 8C8, whereas intense nuclear staining was obtained with mAb 7C7. These different locations of viral target proteins were confirmed by confocal microscopy. The mAb 8C8 reacted with a family of six glycoproteins designated as the gp72 complex in the case of variant A strains and gp63 complex in the case of variant B strains. The endoglycosidases H and F reduced those glycoproteins to a putative precursor molecule of 58 kDa. The mAb 7C7 reacted with 116 and 109 kDa proteins with the two HHV6 variants. These two mAbs did not neutralize virion infectivity in the absence of complement. No cross-reactivity was observed when these mAbs were used in immunoperoxidase assay and immunoblotting against the proteins of human cytomegalovirus or other human herpesviruses. Thus, the two mAbs 8C8 and 7C7 may be valuable tools for the diagnosis and biological investigation of HHV6 infections.

Prospective study of persistence and excretion of human herpesvirus-6 in patients with exanthem subitum and their parents

OBJECTIVE

To elucidate persistence of human herpesvirus-6 (HHV-6) in the blood and excretion of the virus into several body fluids of patients with exanthem subitum (ES), and to examine serologic and virologic findings of the parents caring for the patients in the family setting.

MATERIALS AND METHODS

During a 15-month period, 20 infants from 20 families (11 boys and 9 girls; mean age, 7.7 months; range, 4-11 months) with primary HHV-6 infection and a typical clinical course of ES, and 15 parents from the 20 families (2 males and 13 females; mean age, 28.2 years; range, 21-34 years) were enrolled in the study and examined clinically and virologically. Primary infection with HHV-6 was confirmed by isolation of the virus from peripheral blood mononuclear cells (MNCs), and seroconversion or a significant increase in the antibody titers to HHV-6 by a neutralization test. Viral persistence or excretion was examined by amplifying the viral deoxyribonucleic acid (DNA) in serially collected peripheral blood MNCs, plasma, saliva, stool, and urine samples with a nested polymerase chain reaction method. Data on saliva from the parents were compared with those of 21 age-matched controls.

RESULTS

Twenty infants with virologically confirmed ES had HHV-6 DNA in MNCs persistently during and after the disease but in plasma only in the first 5 days of ES. The viral DNA was also detected persistently or intermittently in saliva and stool during and after the disease but rarely in urine. On the other hand, the 15 parents examined of the 20 infants had no HHV-6 viremia nor viral DNA in peripheral blood MNCs and plasma except 1, but half of them excreted viral DNA in saliva during and after ES. The frequency of excretion of viral DNA into saliva was not significantly different from that of 21 control parents. Only 1 of the 15 showed a fourfold increase in antibody titers to HHV-6 after possible exposure from their children.

CONCLUSIONS

After systemic replication of HHV-6 in the blood of patients with ES during the first 5 days of the disease, the virus is excreted into saliva and stool persistently or intermittently but rarely into urine. The presence of HHV-6 DNA in plasma suggested active infection with the virus. Excretion of the virus into the saliva of infants with ES and their parents suggests the source and transmission route of infection with HHV-6.

Human herpesvirus 6 infection and associated pathogenesis following bone marrow transplantation

Human herpesvirus 6 (HHV-6) infections following bone marrow transplantation (BMT) have been shown to be associated with fever, skin rash, graft versus host disease, encephalitis, delay in engraftment, marrow suppression, and pneumonia. Unfortunately several of these studies were case reports and although the results were suggestive they prompted us to study these pathological events systematically. These associations were primarily based on either HHV-6 isolation, HHV-6 DNA detection, antigen detection or increases in HHV-6 specific antibodies. HHV-6 activity was more frequent during the post- rather than the pre-transplantation period. All HHV-6 isolates from BMT patients have been shown to be variant B. A better understanding of HHV-6 associated pathogenesis gained by larger prospective trials is needed to facilitate proper treatment of cases of idiopathic illnesses or those associated with symptoms (fever, skin rash) similar to those caused by HHV-6.

Human herpesvirus type 6 variants identified by single-strand conformation polymorphism analysis

Six human herpesvirus 6 (HHV-6) variants were analyzed for heterogeneity using the polymerase chain reaction (PCR) and single-strand conformation polymorphism (SSCP). Two independent DNA regions were selected: a fragment of the gene U11 (position 18966-21578) coding for a basic phosphoprotein, the major antigenic structural protein pp100; and a fragment from an open reading frame (ORF) area of the gene U67, previously referred to as 13R (position 102458-103519), coding for a product of unknown function. The two PCR systems based on the above DNA sequences yielded products of 187 bp and 223 bp, respectively. DNA obtained from three laboratory reference strains (U1102, R104 and St.W.) and from HHV-6 infected peripheral white blood cells of bone marrow transplant patients and blood donors was used to test the applicability of two different SSCP analysis systems for the identification of HHV-6 variants using amplicons derived by PCR from the two genomic regions described above (U11 [pp100], U67 [13R-ORF]). The generation of characteristic SSCP patterns enables the rapid differentiation of HHV-6 A and B strains for the classification of variants derived from clinical samples, reducing the need for expensive and time-consuming direct sequencing analyses.

Human herpesvirus 6 open reading frame U12 encodes a functional beta-chemokine receptor

Human herpesvirus 6 (HHV- 6), which belongs to the betaherpesvirus subfamily and infects mainly T cells in vitro, causes acute and latent infections. HHV- 6 contains two genes (U12 and U51) that encode putative homologs of cellular G-protein-coupled receptors (GCR), while three other betaherpesviruses, human cytomegalovirus, murine cytomegalovirus, and human herpesvirus 7, have three, one, and two GCR-homologous genes, respectively. The U12 gene is expressed late in infection from a spliced mRNA. The U12 gene was cloned, and the protein was expressed in cells and analyzed for its biological characteristics. U12 functionally encoded a calcium-mobilizing receptor for beta-chemokines such as regulated upon activation, normal T expressed and secreted (RANTES), macrophage inflammatory proteins 1alpha and 1beta (MIP-1alpha and MIP-1beta) and monocyte chemoattractant protein 1 but not for the alpha-chemokine interleukin-8, suggesting that the chemokine selectivity of the U12 product was distinct from that of the known mammalian chemokine receptors. These findings suggested that the product of U12 may play an important role in the pathogenesis of HHV- 6 through transmembrane signaling by binding with beta-chemokines.

Detection of human herpesvirus 6 DNA in serum by a microplate PCR-hybridization assay

PCR was performed on DNA extracts derived from clinical serum samples submitted for human herpesvirus 6 (HHV-6) serological examination. To detect amplified HHV-6 products, a hybridization-based microtiter plate assay (PCR ELISA; Boehringer Mannheim) was used. The assay system was found to be rapid, specific, and sensitive. Approximately three copies of a plasmid-based HHV-6 sequence could be detected, and no cross amplification was observed with HHV-7 genomic DNA. There was no correlation found between HHV-6 DNA detection and serological status in clinical serum samples from individuals more than 2 years old. On the other hand, in serum samples from infants less than 2 years old, a high rate of detection of HHV-6 DNA was observed in those who lacked immunoglobulin G and M antibodies to HHV-6 (55%). In this regard, PCR of serum DNA extracts may be used as a sensitive indicator of active HHV-6 infection in infants prior to their seroconversion.

Nucleotide sequence analysis of a 30-kilobase-pair region of human herpesvirus-6B (HHV-6B) genome and strain-specific variations in major immediate-early genes

Human herpesvirus 6 (HHV-6) is now classified into two distinct variants such as HHV-6 variant A(HHV-6A) and B(HHV-6B) (Ablashi et al., Arch. Virol. 129, 1993, 1-4) and the DNA of HHV-6A strain U1102 was completely sequenced (Gompels et al., Virology 209, 1995, 29-51). We have sequenced a 30-kilobase pair (kbp) (genomic positions around 111-141 kb) of HHV-6B strain HST, and a sequence of this region was compared with that of HHV-6A strain U1102. Dodecameric repeats, G/T and Kpn repeat elements, putative major immediate early 1 (MIE1) and major immediate early 2 (MIE2) genes were found in this region. The DNA sequences of HHV-6A (U1102) and HHV-6B (HSI) were markedly different in the MIE1 region, Kpn repeat elements and the putative MIE2 region. Dodecameric repeat element was located in the putative MIE2 locus of HHV-6. When primers covering dodecameric repeat region were used to amplify HHV-6 DNA of clinical isolates from patients with exanthem subitum (ES) by polymerase chain reaction (PCR), variations in size of PCR products in each isolate were found, indicating strain-specific features. Furthermore, the results of molecular biological analysis by PCR using DNA samples in a family suggest that HHV-6 infects within a family.

Human herpesvirus-6 (HHV-6) DNA and virus-encoded antigen in oral lesions

Archival oral tissues comprising 51 squamous cell carcinomas, 18 non-malignant lesions and 7 normal mucosa samples were investigated for human herpesvirus-6 (HHV-6)-encoded antigens and HHV-6 DNA. The virus-specific antigens were detected by an immunohistochemical method using monoclonal antibodies. Two further techniques used for HHV-6 DNA detection included the polymerase chain reaction (PCR) with virus-specific primers and in situ hybridization using digoxigenin-labelled oligonucleotides specific for HHV-6A and HHV-6B genotypes. A high proportion (79-80%) of the squamous cell carcinomas were positive for HHV-6 with the various detection methods. In cases of lichen planus and leukoplakia a high prevalence rate (67-100%) was noted with in situ hybridization and immunohistochemical techniques but a lower proportion (22-33%) was detected with the PCR method. All 7 normal tissues tested were negative for HHV-6. The HHV-6 variant B was found in 60% of the oral carcinoma tissues analysed. The study demonstrates the frequent presence of HHV-6 in neoplastic and non-malignant lesions of the oral cavity. While the role of HHV-6 in oral mucosal tissues remains to be determined, the in vitro tumorigenic potential of the virus suggests a possible role in the etiopathogenesis of oral lesions.

Human herpesvirus 6

Human herpesvirus 6 variant A (HHV-6A) and human herpesvirus 6 variant B (HHV-6B) are two closely related yet distinct viruses. These visuses belong to the Roseolovirus genus of the betaherpesvirus subfamily; they are most closely related to human herpesvirus 7 and then to human cytomegalovirus. Over 95% of people older than 2 years of age are seropositive for either or both HHV-6 variants, and current serologic methods are incapable of discriminating infection with one variant from infection with the other. HHV-6A has not been etiologically linked to any human disease, but such an association will probably be found soon. HHV-6B is the etiologic agent of the common childhood illness exanthem subitum (roseola infantum or sixth disease) and related febrile illnesses. These viruses are frequently active and associated with illness in immunocompromised patients and may play a role in the etiology of Hodgkin's disease and other malignancies. HHV-6 is a commensal inhabitant of brains; various neurologic manifestations, including convulsions and encephalitis, can occur during primary HHV-6 infection or in immunocompromised patients. HHV-6 and distribution in the central nervous system are altered in patients with multiple sclerosis; the significance of this is under investigation.

Detection of human herpes virus 6 in AIDS-associated retinitis by means of in situ hybridization, polymerase chain reaction and immunohistochemistry

The ubiquitous nature of HHV-6 and its genomic relationship with cytomegalovirus led us to evaluate an etiological link between HHV-6 and AIDS-associated retinitis in a prospective study. HHV-6 infection was studied in patients with AIDS-associated retinitis and in two control populations. Eye pairs were obtained at necropsy from nine patients with AIDS-associated retinitis, four human immunodeficiency virus (HIV)-sero-positive patients with normal fundus examination and three HIV-seronegative patients. HHV-6 infection was detected by polymerase chain reaction (PCR), in situ hybridization and immunohistochemistry. Human cytomegalovirus (CMV) and HIV-1 infections were detected in parallel by the same methods. HHV-6 infection was detected in three cases of AIDS-associated retinitis. In two of these patients, HHV-6 infection was detected both by immunohistochemistry and PCR while in the third case it was detected by in situ hybridization and PCR. In the three patients, fundus examination showed bilateral retinitis in two of them and unilateral retinitis in one of them. HHV-6 infection was not detected in the retina of the two control groups. CMV was also detected in the three cases positive for HHV-6 by all three methods. HIV DNA was detected by PCR in two of three cases and was confirmed in one of these cases by in situ hybridization. These results confirm that HHV-6 infects the retina but suggests that HHV-6 does not have an exclusive causative role in AIDS-associated retinitis, since CMV coinfection of the retina was detected in all three of the patients positive for HHV-6.

Difference in permissiveness of human fibroblast cells to variants A and B of human herpesvirus-6

Human herpesvirus-6 (HHV6) is a lymphotropic virus genetically related to human cytomegalovirus (CMV) and for which two variants, A and B, have been distinguished. Human CMV is usually cultivated with human fibroblasts (HF). The lack of cell lines useful for HHV6 isolation and propagation led us to investigate whether HHV6 variants A and B could infect HFs as CMV does. Isolates of HHV6 variants A and B were used to infect MRC-5 HFs. HHV6 infection was detected by means of immunoperoxidase assay using three specific monoclonal antibodies. HHV6-specific antigens were detected in 88 and 38% of cases after infection with variants A and B, respectively. The highest number of HHV6-antigen-positive cells was obtained at 4-5 days p.i. The titre of HHV6 stocks was determined in parallel by immunoperoxidase assay on HFs and by observation of cytopathic effect using serial dilutions on peripheral blood mononuclear cells (PBMC). The number of infectious particles inducing the appearance of antigen-positive HF cells was consistently lower than the titre of virus stocks, expressed as TCID50. The amount of HF-associated HHV6 DNA was measured using limiting dilution PCR assay; it was significantly increased during 4-day infection in the case of variant A but not variant B. The yield of virus from infected HFs was demonstrated only for variant A by the serial propagation of virus from HFs to PBMCs and by the increase in cell-free HHV6 DNA in HF culture supernatant. Our results show that HHV6 can reproducibly infect HFs, albeit at a low level, and that HFs are more permissive to variant A than to variant B, as reported previously for PBMCs and human T-cell lines.

Coinfection with human herpesvirus 6 variants A and B in lung tissue

Human herpesvirus 6 (HHV-6) variant B is frequently identified in peripheral blood, but identification of HHV-6 variant A is relatively rare. We devised a PCR-based method for sensitive, simultaneous detection of both HHV-6 variants. The method was applied to 34 lung tissue specimens that were previously shown to contain HHV-6 DNA. A total of 22 lung tissue samples showed coinfections with HHV-6 variants A and B, 2 had only HHV-6 variant A DNA, and 10 had only HHV-6 variant B DNA. The prevalences of coinfections in lung tissues from healthy controls (54% coinfected) and in those from bone marrow transplant patients with pneumonia (67% coinfected) were similar. These data indicate that coinfections of HHV-6 variants A and B commonly occur in lung tissues of healthy and diseased individuals.

Prokaryotic expression of an immediate-early gene of human herpesvirus 6 and analysis of its viral antigen expression in human cells

Segments of an immediate-early (1E) protein (1E03; 958 amino acids (aa)), encoded by clone pSTY03, of human herpesvirus 6 (HHV-6) variant B strain HST were expressed as beta-galactosidase fusion proteins in Escherichia coli. Using Western blot analysis, and the serum of a patient having high titer anti-HHV-6 antibodies, an antigenic region of the IE03 protein was mapped between residues 340 and 505 (pUE03IE-M). The fusion protein expressed in E. coli harboring plasmid pUE03IE-M was purified after electrophoresis in SDS-PAGE, and then immunized in mice to obtain a monospecific antibody. Monospecific antibody raised against the fusion protein reacted with IE03 protein species with apparent molecular weights of 155 and 170 kDa, and was detected as granular fluorescence in nuclei of infected cells by an immunofluorescence antibody test. Furthermore, this antibody reacted only with HHV-6 variant B, but did not react with HHV-6 variant A. The IE03 protein was confirmed to be an IE protein, since the synthesis of this protein was observed in infected cells that were first treated with cycloheximide, which was then replaced with actinomycin D. Further, it was also detected as early as 4 h after infection.

Novel human herpesviruses (human herpesviruses 6, 7 and 8)

The number of members in the family Herpesviridae has increased in the last 10 years due to the description of three novel human herpesviruses: human herpesvirus 6 (HHV-6) in 1986, human herpesvirus 7 (HHV-7) in 1990, and human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV), in 1994. HHV-6 and HHV-7 were first isolated from blood lymphocyte cultures, while HHV-8 was identified following a specific molecular biology approach in the search for the etiologic agent of Kaposi's sarcoma. The three viruses are lymphotropic, T-cells being the targets of HHV-6 and HHV-7, and B-cells being probably those of HHV-8. The ability to be propagated in cell cultures in vitro differs according to the virus concerned: this can be done readily with HHV-6, with more difficulties in the case of HHV-7, and has not yet been achieved in the case of HHV-8. Human infection with HHV-6 and HHV-7 is ubiquitous, widespread and acquired early in life. HHV-8 epidemiology is still unclear, and there are two hypotheses: a restricted dissemination in the general population like herpes simplex virus type 2, or a widespread infection like all other human herpesviruses. The polymerase chain reaction is the common method for the detection of infection using specific primers and probes for HHV-6, HHV-7 and HHV-8 respectively. Serologic assays are only available for HHV-6 and HHV-7, with limitations being due, in particular, to possible cross-reactions with cytomegalovirus. HHV-6 is the causative agent of exanthem subitum (sixth disease). Its role as an opportunistic agent and immune dysfunction inducer is debated and currently under investigation. The pathogenic role of HHV-7 seems to be modest, with one case of exanthem subitum reported so far. HHV-8 is strongly associated with three diseases: Kaposi's sarcoma, Castleman's disease and body-cavity-based lymphomas. The therapy against these novel viruses has to be considered in the future.

Restriction endonuclease mapping and molecular cloning of the human herpesvirus 6 variant B strain Z29 genome

Human herpesvirus 6(HHV-6) variants A and B differ in cell tropism, reactivity with monoclonal antibodies, restriction endonuclease profiles, and epidemiology. Nonetheless, comparative nucleotide and amino acid sequences from several genes indicate that the viruses are very highly conserved genetically, The B variant is the major etiologic agent of exanthem subitum and is frequently isolated from children with febrile illness; no disease has been etiologically associated with HHV-6A. One HHV-6A strain has been cloned and sequenced, but similar information and reagents are not available for HHV-6B. We report here the determination of maps of the restriction endonuclease cleavage sites for BamHI, C1aI, HindIII, KpnI, and Sa1I, and the cloning in plasmids and bacteriophages of fragments representing over 95% of the HHV-6B strain Z29 [HHV-6B(Z29)] genome. Hybridization experiments and orientation of several blocks of nucleotide sequence information onto the genomic map indicate that HHV-6A and HHV-6B genomes are colinear.

Human herpesvirus-6 DNA in the saliva of paediatric oncology patients and controls

Children with malignancy are immunosuppressed and susceptible to serious infections with herpesviruses. The majority of children on chemotherapy for malignancy are seropositive for human herpesvirus-6 (HHV-6), and although HHV-6 has been demonstrated to be a pathogen in severely immunocompromised patients, whether this is the case for paediatric oncology patients is unknown. HHV-6 is secreted in saliva and in this study samples were examined prospectively for HHV-6 DNA in healthy children and those with malignancy. In a nested polymerase chain reaction (PCR), a 287 bp outer fragment and 163 inner fragment of HHV-6 DNA were amplified. The resulting amplimer contained a Hind III restriction site present only in "B" type HHV-6 and this was used to identify the type of HHV-6 amplified. In saliva from healthy control children, 74% (28/38) of samples were HHV-6 DNA-positive in either the supernate, pellet or both. In the patients, 58% (45/77) of all samples were HHV-6 DNA-positive. When sequential samples from twelve patients were examined the children appeared to fall into two groups: those who were frequently HHV-6 DNA-positive (60% of samples or more) and those who were rarely HHV-6 DNA-positive (33% of samples or less) (P < 0.0001). The only apparent difference between these two groups was that the less frequently HHV-6-positive group was more often febrile and unwell with neutropaenia. Hind III digestion demonstrated all the positive samples to be "B" type HHV-6. Possible explanations for this difference in HHV-6 secretion between the patient groups are discussed.

Identification and characterization of a cDNA derived from multiple splicing that encodes envelope glycoprotein gp105 of human herpesvirus 6

The glycoprotein complex gp82-gp105 is a major virion envelope glycoprotein complex of human herpesvirus 6 variant A (HHV-6A) and consists of a number of related polypeptides. Monoclonal antibodies (MAbs) 2D4, 2D6, and 13D6 against this glycoprotein complex neutralized HHV-6A infectivity. We have previously reported the isolation, mapping, and characterization of a portion of the viral genomic DNA fragment encoding the gp82-gp105 complex and the identification of the neutralizing epitope (B. Pfeiffer, Z. N. Berneman, F. Neipel, C. K. Chang, S. Tirwatnapong, and B. Chandran, J. Virol. 67:4611-4620, 1993). This gene was further characterized by the identification of a 2.3-kb genomic fragment and by the identification of a 2.5-kb cDNA clone. The genomic sequence contains a short open reading frame (ORF) encoding the epitope recognized by the MAbs. The identified cDNA showed specificity for HHV-6 in Southern blot analysis with viral DNA. In Northern (RNA) blot analysis with total RNA from HHV-6A(GS)-infected cells, the cDNA insert specifically hybridized with several RNA species. Restriction mapping analysis localized this cDNA to the HHV-6A(U1102) genomic BamHI G fragment, at the right end of the unique long segment of the genome and to the SalI L and SalI O fragments within the left and right terminal direct repeat regions, respectively. In vitro transcription and translation of the cDNA revealed a polypeptide of about 88.5 kDa which was glycosylated in the presence of microsomal membranes to a polypeptide of approximately 104.2 kDa. Both polypeptides were immunoprecipiated by MAb 2D6, verifying the identity of the cDNA as encoding the gp105 in the gp82-gp105 complex. Sequence analysis of the cDNA revealed a large ORF potentially encoding a 650-amino-acid protein with 11 potential N-linked glycosylation sites and 18 cysteine residues. A potential membrane-spanning domain is located only near the amino terminus of the putative protein, indicating that gp105 may be a class 2 glycoprotein. Comparison of the cDNA nucleotide sequence with sequences from HHV-6A(U1102) genomic BamHI G and SalI L fragments revealed that the gene encoding gp105 contains 12 exons, spanning over 20 kb of the viral genome, with intron 1 spanning about 8 kb of genomic DNA. The first exon of the cDNA mapped to the right and left terminal direct repeats, while the other exons mapped within the unique long segment of the genome.(ABSTRACT TRUNCATED AT 400 WORDS)

Selection of a monoclonal antibody specific for variant B human herpesvirus 6-infected mononuclear cells

A monoclonal antibody, designated as MAb 6E2, specific for human herpesvirus 6 variant B (HHV-6B) was derived from the spleen of a mouse immunized with lysates of HHV-6B(Z29) cord blood mononuclear cells. MAb 6E2 reacts by immunofluorescence with all the HIV-6B strains tested (Z29, CV, Hashimoto and SF) and fails to react with variant A prototypes, GS and U1102. The immunofluorescence staining was punctate and localized to the cytoplasm. The protein reacting with MAb 6E2 was identified as protein 48,000 in apparent M(r) value by immunoaffinity chromatography of lysates of HHV-6B-infected mononuclear cells.

Controlled study of human herpesvirus 6 detection in acquired immunodeficiency syndrome-associated non-Hodgkin's lymphoma. The French Study Group for HIV-Associated Tumors

Human herpesvirus 6 (HHV-6) is a recently identified lymphotropic herpesvirus, which has been isolated from patients with acquired immunodeficiency syndrome (AIDS) or lymphoproliferative diseases. Two variants A and B of HHV-6 have been described, variant B being more common in children with exanthema subitum. HHV-6 infection was studied in cases of AIDS-associated non-Hodgkin's lymphoma (NHL), and in three control populations in order to evaluate the possible etiological role of HHV-6 in this lymphoproliferative disease. Tumor specimens from various organs were obtained from 27 patients with AIDS-associated NHL and 20 human immunodeficiency virus (HIV)-seronegative patients with NHL. Lymph node specimens were obtained from four HIV-seropositive and nine HIV-seronegative patients with lymph node follicular hyperplasia. A specific polymerase chain reaction (PCR) was used to detect HHV-6 DNA. Subsequently HHV-6 variant was identified by using variant-specific PCR. Human cytomegalovirus (CMV) infection was detected in parallel by means of specific PCR. HHV-6 DNA was detected in 12 of 27 tumor tissues (44%), including 8 of 15 lymph node specimens (53%) from patients with AIDS-associated NHL. The corresponding values in HIV-seronegative patients with NHL were 35% (7/20) and 36% (5/14), respectively. Lymph node specimens were positive for HHV-6 in two of four (50%) HIV-seropositive and five of nine (55%) HIV-seronegative patients with follicular hyperplasia. Variant A was detected in two cases of AIDS-associated NHL, variant B in one case, and both variants in six cases. The distribution of HHV-6 variants exhibited a similar pattern in the three control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of human herpesvirus 6 variants A and B by amplimer hybridization with variant-specific oligonucleotides and amplification with variant-specific primers

Two distinct PCR-based procedures were evaluated for the detection and identification of human herpesvirus 6 (HHV-6) variants A and B in uncultured human samples. Variant-specific oligonucleotide hybridization (VSOH) is based on the amplification of two distinct regions of the HHV-6 genome, followed by hybridization of amplimers with variant-specific oligonucleotide probes. Variant-specific primer PCR (VSPP) is based on the amplification of each variant by using variant-specific primers. The study of 10 well-characterized HHV-6 strains allowed us to demonstrate the high sensitivity and specificity of both methods. With variant mixtures, however, some limitations of VSOH were evidenced and VSPP was required to obtain unambiguous results. The combination of VSOH and VSPP was applied to the direct study of 300 peripheral blood mononuclear cell samples from French subjects. HHV-6 was detected in 15 samples: 11 corresponded to variant B, 3 corresponded to variant A, and 1 corresponded to a mixture of both variants.

Alphaherpesvirus origin-binding protein homolog encoded by human herpesvirus 6B, a betaherpesvirus, binds to nucleotide sequences that are similar to ori regions of alphaherpesviruses

We previously identified a human herpesvirus 6B (HHV-6B) homolog of the alphaherpesvirus origin-binding protein (OBP), exemplified by the herpes simplex virus type 1 UL9 gene product. This finding is of particular interest because HHV-6B is otherwise more closely related to members of the betaherpesvirus subfamily. The prototypic betaherpesvirus, human cytomegalovirus, does not encode an obvious OBP homolog and contains a more complex origin of replication than do alphaherpesviruses. Thus, analysis of the function of the HHV-6B OBP homolog is essential for understanding the mechanism of HHV-6B DNA replication initiation. The HHV-6B OBP homolog, OBPH6B, was expressed in vitro by coupled transcription and translation and in insect cells by infection with recombinant baculoviruses. The expressed protein bound to two DNA sequences located upstream of the HHV-6B major DNA-binding protein gene homolog, within a region that was predicted to serve as an origin of replication on the basis of its sequence properties. The binding sites lie within 23-bp segments and are similar to OBP-binding sites of herpes simplex virus type 1. The two OBPH6B-binding sequences are separated by an AT-rich region and have an imperfect dyad symmetry as do the alphaherpesvirus origin regions. We identified OBPH6B transcripts by reverse transcription PCR in HHV-6B-infected Molt-3 cells. These results suggest that OBPH6B functions in a manner analogous to the alphaherpesvirus OBP and that initiation of HHV-6B DNA replication may resemble that of alphaherpesviruses.

Variation of DNA sequence in immediate-early gene of human herpesvirus 6 and variant identification by PCR

The complete nucleotide sequence of one of the immediate-early genes of human herpesvirus 6 variant B was determined and compared with that of variant A reported by Martin et al. (M.D. Martin, J. Nicholas, B. J. Thomson, C. Newman, and R. W. Honess, J. Virol. 65:5381-5390, 1991). While it was reported that two open reading frames exist in this region of variant A, only one open reading frame was found in variant B and the putative coding region of variant B was 2,679 nucleotides long. Furthermore, two additive regions of 108 and 228 bp were found in variant B. Primers covering one of these regions deleted in variant A were synthesized and used for PCR amplification. Twelve isolates from patients were clearly classified into variants A and B by PCR amplification with these primers. All isolates from patients with exanthem subitum were variant B.

Identification of a lytic-phase origin of DNA replication in human herpesvirus 6B strain Z29

DNA sequences which have structural features suggestive of their functioning as an origin of lytic-phase DNA replication were previously identified in both human herpesvirus 6B strain Z29 [HHV-6B (Z29)] and in HHV-6A (U1102). Plasmid constructs containing the putative HHV-6B (Z29) oriLyt element were replicated after transfection into permissive T cells, when trans-acting factors were provided by HHV-6B (R-1) infection. By using this assay, the HHV-6B (Z29) oriLyt was mapped to a minimal region of approximately 400 bp which lies upstream of the gene that is homologous to herpes simplex virus UL29, a region that carries an origin in other betaherpesviruses and in some alphaherpesviruses.