Detection of human herpesvirus 7 in salivary glands

Update on human herpesvirus 7 pathogenesis and clinical aspects as a roadmap for future research

Human herpesvirus 7 (HHV-7) is a common virus that is associated with various human diseases including febrile syndromes, dermatological lesions, neurological defects, and transplant complications. Still, HHV-7 remains one of the least studied members of all human betaherpesviruses. In addition, HHV-7-related research is mostly confined to case reports, while in vitro or in vivo studies unraveling basic virology, transmission mechanisms, and viral pathogenesis are sparse. Here, we discuss HHV-7-related literature linking clinical syndromes to the viral life cycle, epidemiology, and viral immunopathogenesis. Based on our review, we propose a hypothetical model of HHV-7 pathogenesis inside its host. Furthermore, we identify important knowledge gaps and recommendations for future research to better understand HHV-7 diseases and improve therapeutic interventions.

Alzheimer's disease as a viral disease: Revisiting the infectious hypothesis

Alzheimer's disease (AD) represents the most frequent type of dementia in elderly people. Two major forms of the disease exist: sporadic - the causes of which have not yet been fully understood - and familial - inherited within families from generation to generation, with a clear autosomal dominant transmission of mutations in Presenilin 1 (PSEN1), 2 (PSEN2) or Amyloid Precursors Protein (APP) genes. The main hallmark of AD consists of extracellular deposits of amyloid-beta (Aβ) peptide and intracellular deposits of the hyperphosphorylated form of the tau protein. An ever-growing body of research supports the viral infectious hypothesis of sporadic forms of AD. In particular, it has been shown that several herpes viruses (i.e., HHV-1, HHV-2, HHV-3 or varicella zoster virus, HHV-4 or Epstein Barr virus, HHV-5 or cytomegalovirus, HHV-6A and B, HHV-7), flaviviruses (i.e., Zika virus, Dengue fever virus, Japanese encephalitis virus) as well as Human Immunodeficiency Virus (HIV), hepatitis viruses (HAV, HBV, HCV, HDV, HEV), SARS-CoV2, Ljungan virus (LV), Influenza A virus and Borna disease virus, could increase the risk of AD. Here, we summarized and discussed these results. Based on these findings, significant issues for future studies are also put forward.

Age-Related Patterns of DNA Detection and Specific IgG Subclasses in Healthy HHV-6- and HHV-7-Infected Individuals

Human herpesvirus 6A (HHV-6A), Human herpesvirus 6B (HHV-6B), and Human herpesvirus 7 (HHV-7) can persist by establishing a lifelong infection which could have implications on the immunocompetent host. The aim of this work is to contribute with some knowledge about the HHV-6 A/B and HHV-7 infection in healthy individuals. We have carried out a longitudinal study in seropositive healthy individuals for the detection of viral DNA in saliva and plasma samples, and for determining a specific IgG isotype immune response, which enabled the performance of these viruses to be observed over time. Furthermore, an elderly population was transversely studied to provide data of the activity of these viruses in the older population. In the longitudinal study, HHV-6 DNA was occasionally detected and an isotype immune response with a specific IgG1 profile, while in the older group HHV-6 DNA was frequently detected and an isotype immune response with specific IgG1, IgG3, and IgG4. HHV-7 DNA was frequently detected in both groups and isotype patterns of specific IgG1, IgG3, and IgG4. The results of this study highlight that the long-lasting relationship in healthy HHV-6 A/B-infected individuals have the imprint of age groups.

Macaque homologs of Kaposi's sarcoma-associated herpesvirus (KSHV) infect germinal center lymphoid cells, epithelial cells in skin and gastrointestinal tract and gonadal germ cells in naturally infected macaques

We developed a set of rabbit antisera to characterize infections by the macaque RV2 rhadinovirus homologs of KSHV. We analyzed tissues from rhesus and pig-tailed macaques naturally infected with rhesus rhadinovirus (RRV) or Macaca nemestrina rhadinovirus 2 (MneRV2). Our study demonstrates that RV2 rhadinoviruses have a tropism for epithelial cells, lymphocytes and gonadal germ cells in vivo. We observed latent infections in both undifferentiated and differentiated epithelial cells with expression of the latency marker, LANA. Expression of the early (ORF59) and late (glycoprotein B) lytic markers were detected in highly differentiated cells in epithelial ducts in oral, renal, dermal and gastric mucosal tissue as well as differentiated germ cells in male and female gonads. Our data provides evidence that epithelial and germ cell differentiation in vivo induces rhadinovirus reactivation and suggests that infected epithelial and germ cells play a role in transmission and dissemination of RV2 rhadinovirus infections in vivo.

Complete Unique Genome Sequence, Expression Profile, and Salivary Gland Tissue Tropism of the Herpesvirus 7 Homolog in Pigtailed Macaques

Human herpesvirus 6A (HHV-6A), HHV-6B, and HHV-7 are classified as roseoloviruses and are highly prevalent in the human population. Roseolovirus reactivation in an immunocompromised host can cause severe pathologies. While the pathogenic potential of HHV-7 is unclear, it can reactivate HHV-6 from latency and thus contributes to severe pathological conditions associated with HHV-6. Because of the ubiquitous nature of roseoloviruses, their roles in such interactions and the resulting pathological consequences have been difficult to study. Furthermore, the lack of a relevant animal model for HHV-7 infection has hindered a better understanding of its contribution to roseolovirus-associated diseases. Using next-generation sequencing analysis, we characterized the unique genome of an uncultured novel pigtailed macaque roseolovirus. Detailed genomic analysis revealed the presence of gene homologs to all 84 known HHV-7 open reading frames. Phylogenetic analysis confirmed that the virus is a macaque homolog of HHV-7, which we have provisionally named Macaca nemestrina herpesvirus 7 (MneHV7). Using high-throughput RNA sequencing, we observed that the salivary gland tissue samples from nine different macaques had distinct MneHV7 gene expression patterns and that the overall number of viral transcripts correlated with viral loads in parotid gland tissue and saliva. Immunohistochemistry staining confirmed that, like HHV-7, MneHV7 exhibits a natural tropism for salivary gland ductal cells. We also observed staining for MneHV7 in peripheral nerve ganglia present in salivary gland tissues, suggesting that HHV-7 may also have a tropism for the peripheral nervous system. Our data demonstrate that MneHV7-infected macaques represent a relevant animal model that may help clarify the causality between roseolovirus reactivation and diseases.

IMPORTANCE Human herpesvirus 6A (HHV-6A), HHV-6B, and HHV-7 are classified as roseoloviruses. We have recently discovered that pigtailed macaques are naturally infected with viral homologs of HHV-6 and HHV-7, which we provisionally named MneHV6 and MneHV7, respectively. In this study, we confirm that MneHV7 is genetically and biologically similar to its human counterpart, HHV-7. We determined the complete unique MneHV7 genome sequence and provide a comprehensive annotation of all genes. We also characterized viral transcription profiles in salivary glands from naturally infected macaques. We show that broad transcriptional activity across most of the viral genome is associated with high viral loads in infected parotid glands and that late viral protein expression is detected in salivary duct cells and peripheral nerve ganglia. Our study provides new insights into the natural behavior of an extremely prevalent virus and establishes a basis for subsequent investigations of the mechanisms that cause HHV-7 reactivation and associated disease.

Detection of human herpesvirus 6 DNA but not human herpesvirus 7 or 8 DNA in atherosclerotic and nonatherosclerotic vascular tissues

INTRODUCTION

Various viral infections are thought to play a role in the development of atherosclerosis. A number of studies suggest that certain viruses from the Herpesviridae family in particular may lead to atherosclerosis.

METHODS

We investigated the presence of human herpesvirus 6 (HHV-6), human herpesvirus 7 (HHV-7), and human herpesvirus 8 (HHV-8) DNA in carotid, iliac, and coronary artery specimens obtained from a group of adult autopsy cases by means of polymerase chain reaction (PCR) analysis and nested PCR techniques. A 28-subject study group with at least type IV atherosclerosis and a 25-subject control group with no visible atherosclerosis were enrolled.

RESULTS

HHV-6 DNA was found in the carotid artery specimen of 1 subject with atherosclerosis, in an iliac artery specimen of another subject, and in the iliac artery specimen of one of the control subjects. HHV-7 or HHV-8 DNA was not found in either the atherosclerosis or control cases.

CONCLUSIONS

This study is the first to demonstrate the presence of HHV-6 in atherosclerotic vascular tissues. HHV-7 and HHV-8 were not found in atherosclerotic tissues; however, further research on broader study groups and with different protocols is needed to determine whether these viruses play a role in the formation of atherosclerosis.

Human herpesvirus 7 u21 downregulates classical and nonclassical class I major histocompatibility complex molecules from the cell surface

Herpesviruses have evolved numerous strategies to evade detection by the immune system. Notably, most of the herpesviruses interfere with viral antigen presentation to cytotoxic T lymphocytes (CTLs) by removing class I major histocompatibility complex (MHC) molecules from the infected cell surface. Clearly, since the herpesviruses have evolved an extensive array of mechanisms to remove class I MHC molecules from the cell surface, this strategy serves them well. However, class I MHC molecules often serve as inhibitory ligands for NK cells, so viral downregulation of all class I MHC molecules should leave the infected cell open to NK cell attack. Some viruses solve this problem by selectively downregulating certain class I MHC products, leaving other class I products at the cell surface to serve as inhibitory NK cell ligands. Here, we show that human herpesvirus 7 (HHV-7) U21 binds to and downregulates all of the human class I MHC gene products, as well as the murine class I molecule H-2K(b). HHV-7-infected cells must therefore possess other means of escaping NK cell detection.

Anatomical mapping of human herpesvirus reservoirs of infection

Following primary infection, all eight human herpesviruses persist lifelong in the human host. However, a mapping of all anatomic sites of human herpesvirus persistence is lacking. Fresh tissue specimens representing approximately 40 major anatomic sites from eight autopsies were screened using a recently developed real-time PCR method for detection of all eight human herpesviruses. Patients with evidence of active herpesvirus infection (herpes simplex 1 (HSV-1), herpes simplex 2 (HSV-2), varicella-zoster virus (VZV), Epstein-Barr virus (EBV), cytomegalovirus (CMV), herpesvirus 6 (HHV-6), herpesvirus 7 (HHV-7), and herpesvirus 8 (HHV-8)) at the time of death were excluded to avoid detection of widely disseminated infection. Despite this precaution, widespread HSV-1 positivity (with blood positivity) was detected in one case-an elderly male who died of cardiac arrest. In a middle-aged male with HIV-AIDS, HSV-1 was found in neural and pharyngeal tissues, skin, cartilage, bone, and urinary bladder, whereas in two other cases, HSV-1 was restricted to neural tissues. HSV-2 was detected in a single site, the anus, in the male with HIV-AIDS. VZV was detected only twice, once in the adrenal gland and once in the small intestine. CMV was detected in three cases, most commonly in nasal mucosa, trachea, thyroid, intestine, and liver. EBV was detected in all eight cases, especially in nasal mucosa, tonsil, spleen, lymph node, tongue, and intestine, but in only two of six whole-blood specimens. HHV-6, like EBV, was detected in all eight cases, most commonly in salivary glands, thyroid, stomach, intestines, liver, and pancreas. HHV-7, like EBV and HHV-6, was detected in all eight cases, most commonly in salivary glands, tonsil, lymph nodes, and bone marrow. HHV-8 was detected in only two sites (both lymph nodes) from two cases. Herpesviruses were detected in three of six whole-blood specimens, including HSV-1, EBV, HHV-6, and HHV-7. These results represent the most comprehensive mapping of herpesvirus tissue distribution in humans reported to date.

Immunohistochemical assessment of fractalkine, inflammatory cells, and human herpesvirus 7 in human salivary glands

Human fractalkine (CX3CL1), a delta-chemokine, is implicated in the mediation of multiple cell functions. In addition to serving as a chemotactic factor for mononuclear cell subtypes, membrane-bound fractalkine may promote viral infection by interacting with virions that encode putative fractalkine-binding proteins. Fractalkine expression in normal epithelial tissues studied to date is either constitutive or is upregulated with inflammation. In salivary glands, the expression of fractalkine is unknown. Moreover, salivary glands are a major site for the persistent and productive infection by human herpesvirus (HHV)-7, which encodes two putative fractalkine-binding gene products, U12 and U51. Surprisingly, the cellular distribution of HHV-7 in major salivary glands has not been explored. We therefore determined by immunohistochemistry the cellular localization of fractalkine in three different salivary glands: parotid, submandibular, and labial glands. Fractalkine expression was highly variable, ranging from high to undetectable levels. We further examined the association of fractalkine with inflammatory cell infiltration or HHV-7 infection of salivary epithelial cells. Inflammatory cells were always adjacent to epithelial cells expressing fractalkine, consistent with a function of fractalkine in inflammatory cell recruitment and/or retention in salivary glands. In contrast, HHV-7-infected epithelial cells did not always express fractalkine, suggesting that fractalkine may not be an absolute requirement for viral entry.

Human herpesvirus 7 is latent in gastric mucosa

Chronic gastritis is associated frequently with persistent infection by Helicobacter pylori. However, not all patients with chronic gastritis have evidence of H. pylori infection, suggesting that other factors might contribute to the development of gastritis. The present study was undertaken to evaluate a possible etiologic role of human herpesvirus 7 (HHV-7). HHV-7 DNA was detected in about 80% of gastric biopsies, both in healthy mucosa from individuals without evidence of inflammation and in biopsies from patients with histologically confirmed chronic gastric inflammation. HHV-7 was present also in H. pylori negative samples, was associated specifically with gastric tissue and not with residual blood within the mucosa, and was present with high viral loads. HHV-7 DNA persisted in several patients also after remission of gastric inflammation and the viral presence did not correlate with specific symptoms. Analysis by RT-PCR showed that HHV-7 is transcriptionally inactive in chronic gastritis lesions. These observations show that gastric tissue represents a site of HHV-7 latent infection and a potential reservoir for viral reactivation.

Identification and analysis of a novel heparin-binding glycoprotein encoded by human herpesvirus 7

Human herpesvirus 6 (HHV-6) and HHV-7 are closely related betaherpesviruses that encode a number of genes with no known counterparts in other herpesviruses. The product of one such gene is the HHV-6 glycoprotein gp82-105, which is a major virion component and a target for neutralizing antibodies. A 1.7-kb cDNA clone from HHV-7 was identified which contains a large open reading frame capable of encoding a predicted primary translational product of 468 amino acids (54 kDa) with 13 cysteine residues and 9 potential N-linked glycosylation sites. This putative protein, which we have termed gp65, was homologous to HHV-6 gp105 (30% identity) and contained a single potential membrane-spanning domain located near its amino terminus. Comparison of the cDNA sequence with that of the viral genome revealed that the gene encoding gp65 contains eight exons, spanning almost 6 kb of the viral genome at the right (3') end of the HHV-7 genome. Northern (RNA) blot analysis with poly(A)(+) RNA from HHV-7-infected cells revealed that the cDNA insert hybridized to a single major RNA species of 1.7 kb. Antiserum raised against a purified, recombinant form of gp65 recognized a protein of roughly 65 kDa in sucrose density gradient-purified HHV-7 preparations; treatment with PNGase F reduced this glycoprotein to a putative precursor of approximately 50 kDa. Gp65-specific antiserum also neutralized the infectivity of HHV-7, while matched preimmune serum did not do so. Finally, analysis of the biochemical properties of recombinant gp65 revealed a specific interaction with heparin and heparan sulfate proteoglycans and not with closely related molecules such as N-acetylheparin and de-N-sulfated heparin. At least two domains of the protein were found to contribute to heparin binding. Taken together, these findings suggest that HHV-7 gp65 may contribute to viral attachment to cell surface proteoglycans.

Human herpesvirus 7

Human herpesvirus 7, reported in 1990 is a lymphotropic member of the betaherpesvirus subfamily of herpesviruses. The virus is highly seroprevalent, primary infection usually occurs during childhood, and it has been associated with cases of exanthem subitum, pityriasis rosea, neurological manifestations and transplant complications. The latter two may warrant antiviral intervention, in vitro studies have shown that HHV-7 is susceptible to several nucleoside phosphonate compounds. In vitro, the virus has approximately a 5 day growth cycle in cultured lymphocytes; in vivo, latency is established in peripheral blood T-cells and a persistent infection is established in salivary gland tissue from which infectious virus is constitutively shed in saliva. The HHV-7 genome is approximately 145 kb and encodes at least 84 different proteins. Studies characterising HHV-7 gene products and the required interactions between viral and cellular genes necessary for virus replication, persistence and latency are in their infancy. HHV-7 infection has a variety of effects on host cells including upregulation of interleukin 15 and down-modulation of the cell surface molecule CD4; the latter serves as the cellular membrane receptor for HHV-7. Since HIV also infects T-cells via the CD4 molecule, the interactions of these viruses within T-cells during the course of AIDS are important areas of investigation.

Selective activity of various antiviral compounds against HHV-7 infection

Human herpesvirus virus type 7 (HHV-7) is a T-lymphotropic herpesvirus which uses the CD4 receptor as main receptor to infect its target cells. Measuring the decrease of CD4 expression during HHV-7 infection is a convenient and accurate method to monitor the efficacy of antiviral agents against HHV-7 infection. Different classes of compounds, such as heparin, pentosan polysulfate (PS), dextran sulfate (DS), aurintricarboxylic acid (ATA), phosphonoformic acid (PFA), 9-(2-phosphonylmethoxyethyl)adenine (PMEA), 2-amino-7-[(1,3-dihydroxy-2-propoxy) methyl] purine (S2242), polyvinylalcohol sulfate (PVAS) and the co-polymer of vinylalcohol sulfate with acrylic acid (PAVAS), acyclovir (ACV), ganciclovir (GCV), penciclovir (PCV), brivudin (BVDU), cidofovir (HPMPC), lobucavir, (R)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine] (H2G), (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) and sorivudine (BVaraU), were evaluated for their anti-HHV-7 activity in the SupT1 T cell line and in purified CD4+ T lymphocytes. Antiviral activity was monitored by inhibition of: (i) CD4 expression down-regulation; (ii) giant cell formation and (iii) apoptosis induction. In general, PS, DS, PVAS, PAVAS, ATA, PFA, PMEA, S2242, lobucavir and HPMPC had comparable anti-HHV-7 activity in the two cell lines, irrespective of the parameters followed to monitor antiviral activity. One of the exceptions was heparin which had an IC50 of 9.6 microg/ml in SupT1 cells and >250 microg/ml in CD4+ T lymphocytes. The compounds PCV, GCV, H2G and PMPA showed some activity in CD4+ T lymphocytes, but not in SupT1 cells. ACV, BVDU and BVaraU did not show activity in either cell system. None of the chemokines tested, such as platelet factor-4 (PF-4), eotaxin, stromal cell-derived factor 1alpha(SDF-1alpha) and RANTES, had detectable activity against HHV-7. In contrast, the HIV-1 envelope glycoprotein, gp120, and the two anti-CD4 mAbs, 13B8-2 and OKT4, were clearly active against HHV-7 infection.

Propagation and characterization of human herpesvirus-7 (HHV-7) isolates in a continuous T-lymphoblastoid cell line (SupT1)

After initial culture of HHV-7 in PHA-stimulated human cord blood mononuclear cells (HCBMC), six HHV-7 isolates were propagated successfully in an immature continuous T-lymphoblastoid cell line SupT1. All six isolates infected efficiently the SupT1 cells, and the infected cells became grossly enlarged and multinucleated 7-21 days post-infection. Various stages of HHV-7 morphogenesis were detected. Cell-free supernatants from HHV-7-infected SupT1 cells were infectious to HCBMC as well as to SupT1 cells. The HHV-7-infected SupT1 and HCBMC cell lysates contained more infectious virus than the centrifuged cell culture fluid supernates from the same culture. The HHV-7 isolates H7-2, H7-3, JHC, and JB, concentrated 500 times, had average infectivity titers of 10(3.0) TCID50/ml while strains H7-4 and KHR titered approximately 1-2 logs higher. When all six HHV-7 isolates were propagated in SupT1 and culture fluid supernatants were examined 14-21 days post-infection by negative stain electron microscopy they contained an average of 1.9 x 10(9) virus particles/liter. IFA and ELISA, using HHV-7/SupT1 cell lysate as an antigen, seem to correlate well in detecting high and low HHV-7 antibody in sera from chronic fatigue patients and healthy donors as controls. HHV-7 from SupT1 cell culture was free of HHV-6 and other human herpesviruses as tested by PCR, and the HHV-7 PCR signal was still strong when the viral preparation was diluted to 4.82 x 10(2) genome copies. Since HCBMC are expensive to obtain and available in only small amounts, it is difficult to obtain large quantities of HHV-7 antigen. On the other hand, the SupT1 cell is an excellent source to produce consistently sufficient quantities of HHV-7 for purification studies, development of immunodiagnostics, in vivo infectivity studies, evaluation of antiviral drugs, and molecular biological studies.