Human herpesvirus 6

Close Encounters of the First Kind: Innate Sensors and Multiple Sclerosis

Although autoimmune diseases by definition imply adaptive immune system pathologies, growing evidence points to the relevance of innate receptors in modulating the initiation and progression of the autoreactive response. Multiple sclerosis (MS) is a chronic autoimmune disease characterised by central nervous system (CNS) demyelination, inflammation and axonal damage, in which the role of several pathogens such as herpes viruses have long been described as potential triggers. Encounters of these pathogens with altered innate receptors in susceptible individuals might drive pathological autoreactivity and inflammation, overcoming tolerance and causing subsequent CNS damage. In particular, functional and genetic studies reveal that Toll-like receptor (TLR) 2 and the Nod-like receptor (NLR) P3 could be involved in MS pathogenesis, whereas TLR3, the triggering receptor expressed on myeloid cells (TREM)-2 and the C-type lectin receptors (CLRs) MBL and MASP-3 would have a putative protective role. A better understanding of these interactions will provide important insights into the aetiopathogenesis of MS and could help design potential targets for novel therapies.

Epidemiology of herpes human virus 6 and 7 infections in salivary gland neoplasms in isfahan, iran

Background:

The previous studies showed that herpes human virus-6 (HHV-6) and HHV-7 exist in salivary glands. One of the important areas in oral and maxillofacial pathology field is tumors of the salivary glands. In this study, to declare the major sites of persistent infection with HHV-6 and HHV-7, the existence of HHV-6 and HHV-7 genomes in formalin-fixed paraffin embedded tissue samples of salivary gland tumors.

Methods:

This analytical study was performed in 60 paraffin blocks samples of malignant and benign neoplasms of both major and minor salivary glands. This study performed with highly sensitive real time PCR method.

Results:

Among 60 paraffin blocks salivary gland tumors with equal chances of presence of the HHV-7 and HHV-6 in the samples, 34% were positive for both HHV-7 and HHV-6 while 47.2% were only positive for HHV-7, 18.9% samples were positive for HHV-6. A relationship was noticed between HHV-7 and HHV-6 genomes.

Conclusion:

In conclusion, this study showed no relation between virus and diseases with P=0.953. Also it could be inferred that there is a relationship between HHV-6 and 7 in salivary glands neoplasms.

CXCR4: a virus's best friend?

Viruses are dependent on their hosts for replication and dispersal in the environment; thus, the most successful viruses are those that co-evolve with their hosts. CXCR4 is a cellular chemokine receptor that plays central roles in development, hematopoiesis, and immune surveillance through signaling induced by its ligand, CXCL12. The CXCR4-CXCL12 axis has been besieged by many pathogens that employ a range of strategies to modify or exploit CXCR4 activity. While CXCR4 was identified as a critical co-factor for entry of HIV into CD4+ T cells early on, other viruses may utilize CXCR4 to gain cell entry as well. Moreover, several viruses have been found to modulate CXCR4 expression or alter its functional activity, with direct effects on cell trafficking, immune responses, cell proliferation, and cell survival. Because CXCR4 is targeted by a diverse group of viral pathogens, modification of host CXCR4 signaling activity is emerging as a common theme in virus persistence and is likely to be important for subversion of the host immune system. This review highlights major viral pathogens that use and abuse CXCR4 and explores the possible reasons why this chemokine receptor has become "a virus's best friend".

Human herpesvirus 6 impairs differentiation of monocytes to dendritic cells

OBJECTIVE

Monocyte-derived dendritic cells (DCs) play important roles in the immune response against infections and malignancies. Human herpesvirus 6 (HHV-6) infects monocytes and is reactivated in immunodeficient patients. To clarify the mechanisms of HHV-6-induced immunodeficiency, we investigated the effect of HHV-6 infection on differentiation of monocytes to DCs.

METHODS

Monocytes were inoculated with or without HHV-6 and then allowed to differentiate to myeloid DCs in culture medium containing granulocyte-macrophage colony-stimulating factor and interleukin (IL)-4. The expression of cell surface molecules on DCs and the capacity of the DCs for antigen capture were examined by flow cytometric analysis. Alteration of antigen-presenting capacity induced by HHV-6 infection was examined.

RESULTS

The morphology of HHV-6-infected monocyte-derived DCs was distinctly different from that of the DCs derived from mock-infected monocytes. Although expression levels of DC-associated surface antigens, including CD80, CD83, and CD86, were significantly higher on HHV-6-infected monocyte-derived DCs than on DCs derived from mock-infected monocytes, antigen-presenting capacity was significantly lower in the former group. Addition of culture supernatant of HHV-6-infected monocytes resulted in suppression of the T-lymphocyte proliferative response, and anti-IL-10 neutralizing antibody partly inhibited this suppressive effect. The antigen-presenting capacity of DCs generated from a patient with severe HHV-6 reactivation was significantly lower than that of DCs generated from the same patient in the recovery phase.

CONCLUSIONS

HHV-6 infection induces immunodeficiency via impaired differentiation of DCs. These results present a new concept for the pathogenesis of HHV-6-induced immunodeficiency.

Use of amplicon-6 vectors derived from human herpesvirus 6 for efficient expression of membrane-associated and -secreted proteins in T cells

The composite amplicon-6 vectors, which are derived from human herpesvirus 6 (HHV-6), can target hematopoietic cells. In the presence of the respective helper viruses, the amplicons are replicated by the rolling circle mechanism, yielding defective genomes of overall size 135 to 150 kb, composed of multiple repeats of units, containing the viral DNA replication origin, packaging signals, and the selected transgene(s). We report the use of amplicon-6 vectors designed for transgene expression in T cells. The selected transgenes included the green fluorescent protein marker, the herpes simplex virus type 1 glycoprotein D (gD), and the gD gene deleted in the transmembrane region (gDsec). The vectors were tested after electroporation and passage in T cells with or without helper HHV-6A superinfections. The results were as follows. (i)The vectors could be passaged both as cell-associated and as cell-free secreted virions infectious to new cells. (ii)The intact gD accumulated at the cell surface, whereas the gDsec was dispersed at internal locations of the cells or was secreted into the medium. (iii)Analyses of amplicon-6-gD expression by flow cytometry have shown significant expression in cultures with reiterated amplicons and helper viruses. The vector has spread to >60% of the cells, and the efficiency of expression per cell increased 15-fold, most likely due to the presence of concatemeric amplicon repeats. Current studies are designed to test whether amplicon-6 vectors can be used for gene therapy in lymphocytes and whether amplicon-6 vectors expressed in T cells and dendritic cells can induce strong cellular and humoral immune responses.

Phenotypic and functional alterations of dendritic cells induced by human herpesvirus 6 infection

Human herpesvirus 6 (HHV-6) has a tropism for T lymphocytes and monocytes/macrophages, suggesting that HHV-6 infection affects the immunosurveillance system. In the present study, we investigated the HHV-6-induced phenotypic and functional alterations of dendritic cells (DCs), which are professional antigen-presenting cells. HHV-6 infection of monocyte-derived immature DCs appeared to induce the up-regulation of CD80, CD83, CD86, and HLA class I and class II molecules, suggesting that HHV-6 infection induces the maturation of DCs. In addition, the antigen capture capacity of DCs was found to decrease following infection with HHV-6. In contrast to up-regulation of mature-DC-associated surface molecules on HHV-6-infected DCs, their capacity for presentation of alloantigens and exogenous virus antigens to T lymphocytes decreased significantly from that of uninfected DCs. In contrast, there appeared to be no reduction in the capacity for presentation of an HLA class II-binding peptide to the peptide-specific CD4(+) T lymphocytes. These data indicate that HHV-6 infection induces phenotypic alterations and impairs the antigen presentation capacity of DCs. The present data also suggest that the dysfunction of HHV-6-infected DCs is attributable mainly to impairment of the antigen capture and intracellular antigen-processing pathways.

Antiviral prophylaxis may prevent human herpesvirus-6 reactivation in bone marrow transplant recipients

Human herpesvirus-6 (HHV-6) infects the majority of children under the age of 2 years causing roseola infantum. Following short self-limited disease, the virus enters into a latency phase in peripheral blood lymphocytes (PBL). It has been previously reported that HHV-6 reactivation from latency, in immunocompromised patients undergoing bone marrow transplantation (BMT), could result in febrile illness, pneumonitis, meningitis, and/or encephalitis. In our study, 14 BMT patients received two different antiviral prophylactic therapies: 8 patients received acyclovir, whereas 6 patients received ganciclovir. Clinical manifestations and virus recovery were monitored pre- and post-BMT by polymerase chain reaction tests of cord blood cells cultured with the patients' PBL. No HHV-6 recovery was shown in the 6 patients treated with ganciclovir, whereas 3 of the 8 acyclovir-treated patients experienced virus reactivation 20-21 days post-BMT. One of the 3 patients was asymptomatic but had late engraftment; the second patient had prolonged fever, skin rash, and hemorrhage; the third patient experienced prolonged fever, pneumonitis, marrow rejection, and fatal encephalitis. It is concluded that viral reactivation may be prevented by prophylactic treatment with ganciclovir. Our observation awaits further documentation in prospective randomized trials in high-risk BMT recipients.

Transcriptional down-regulation of CXC chemokine receptor 4 induced by impaired association of transcription regulator YY1 with c-Myc in human herpesvirus 6-infected cells

We have recently reported that down-regulation of CXC chemokine receptor (CXCR) 4 in CD4(+) T lymphocytes is induced by human herpesvirus (HHV) 6 infection. In this study, we further studied the mechanisms of HHV-6-induced CXCR4 down-regulation, focusing on the regulation of CXCR4 transcription. Down-regulation of CXCR4 transcription was detected in HHV-6A-infected JJHAN and HHV-6B-infected MT-4 cell lines, as we had previously reported for HHV-6-infected peripheral blood CD4(+) T lymphocytes. Luciferase assays revealed that a YY1-binding site around -320 relative to the transcription start site is important for down-regulation of CXCR4 transcription in HHV-6-infected cells. The binding activity of YY1, which is a repressor of CXCR4 transcription, to the CXCR4 promoter appeared to significantly increase in HHV-6-infected cells compared with the binding activity in mock-infected cells. Immunoprecipitation assays showed that in HHV-6-infected cells association of c-Myc with YY1 was decreased and that of Max with c-Myc was increased, whereas association of Mad with Max appeared to be decreased. The amounts of each of YY1, c-Myc, Max, and Mad proteins synthesized in cells were not altered by HHV-6 infection. These data indicate that the decreased association of YY1 with c-Myc that is caused by impaired interaction in the c-Myc/Max/Mad network results in increased binding activity of YY1 to the CXCR4 promoter, mediating down-regulation of CXCR4 production in HHV-6-infected cells.

Role of viruses in etiology and pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is the most prevalent demyelinating disease of young adults, affecting an estimated 300,000 individuals in the United States alone. The majority of affected individuals have a relapsing–remitting course while a smaller subset has a more chronic–progressive presentation. Women are affected more often than men, a phenomenon associated with a number of auto-immune diseases. Although the etiology of MS is unknown, it is generally believed that genetic, immunologic, and environmental factors are involved. This chapter discusses these issues as they suggest that exogenous factors are associated with the pathogenesis of this disorder. Recently, the human herpes virus 6 (HHV-6) has received considerable attention as an infectious agent candidate that might be associated with the pathogenesis of MS. The chapter focuses on this agent and the data that support the role of this virus in MS disease pathogenesis. A model is proposed, whereby in genetically susceptible individuals, multiple viruses may trigger either a virus-specific or a cross-reactive auto-immune response that results in clinical MS. Epidemiologic evidence suggests that it is a multifactorial disease that develops as a result of host genetics, immune response, and environment.

Frequent HHV-6 reactivation in multiple sclerosis (MS) and chronic fatigue syndrome (CFS) patients

BACKGROUND

HHV-6 is a ubiquitous virus and its infection usually occurs in childhood and then becomes a latent infection. HHV-6 reactivation has been shown to play a role in the pathogenesis of AIDS and several other diseases.

OBJECTIVES

To determine what role HHV-6 infection or reactivation plays in the pathogenesis of multiple sclerosis (MS) and chronic fatigue syndrome (CFS).

RESULTS

Twenty-one MS and 35 CFS patients were studied and followed clinically. In these patients, we measured HHV-6 IgG and IgM antibody levels and also analyzed their peripheral blood mononuclear cells (PBMCs) for the presence of HHV-6, using a short term culture assay. In both MS and CFS patients, we found higher levels of HHV-6 IgM antibody and elevated levels of IgG antibody when compared to healthy controls. Seventy percent of the MS patients studied contained IgM antibodies for HHV-6 late antigens (capsid), while only 15% of the healthy donors (HD) and 20% of the patients with other neurological disorders (OND) had HHV-6 IgM antibodies. Higher frequency of IgM antibody was also detected in CFS patients (57.1%) compared to HD (16%). Moreover, 54% of CFS patients exhibited antibody to HHV-6 early protein (p41/38) compared to only 8.0% of the HD. Elevated IgG antibody titers were detected in both the MS and the CFS patients. PBMCs from MS, CFS and HD were analyzed in a short term culture assay in order to detect HHV-6 antigen expressing cells and to characterize the viral isolates obtained as either Variant A or B. Fifty-four percent of MS patients contained HHV-6 early and late antigen producing cells and 87% of HHV-6 isolates were Variant B. Isolates from CFS, patients were predominately Variant A (70%) and isolates from HD were predominately Variant B (67%). Moreover, one isolate from OND was also Variant B. Persistent HHV-6 infection was found in two CFS patients over a period of 2.5 years and HHV-6 specific cellular immune responses were detected in PBMCs from ten CFS patients.

CONCLUSION

In both MS and CFS patients, we found increased levels of HHV-6 antibody and HHV-6 DNA. A decrease in cellular immune responses was also detected in CFS patients. These data suggest that HHV-6 reactivation plays a role in the pathogenesis of these disorders.

Tamplicon-7, a novel T-lymphotropic vector derived from human herpesvirus 7

We describe the derivation of a novel T-cell-defective virus vector employing the human herpesvirus 7 (HHV-7). The new vector, designated Tamplicon-7, replicates in CD4(+) T cells. The system is composed of a helper virus and defective virus genomes derived by the replication of the input Tamplicon vector. There are two cis-acting functions required for the replication and packaging of the defective virus genomes in the presence of the helper virus: the viral DNA replication origin and the composite cleavage and packaging signal, which directs the cleavage and packaging of defective virus genomes. Viral DNA replication is compatible with the rolling circle mechanism, producing large head-to-tail concatemers of the Tamplicon vector. Thus, in the presence of the helper virus, the replicated vectors are packaged and secreted into the medium. Furthermore, we have shown that the vector can be employed to express a foreign gene, encoding the green fluorescent protein, in the T cells infected with the HHV-7 helper virus. We predict that the Tamplicon-7 vector might be potentially useful for gene therapy of diseases affecting the human CD4(+) T cells, including autoimmune diseases, T-cell lymphomas, and AIDS.

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.

In vitro activation of human herpesviruses 6 and 7 from latency

Human herpesviruses 6 and 7 (HHV-6 and HHV-7) are prevalent lymphotropic viruses that infect more than 80% of children at infancy or during early childhood. Infection ranges from asymptomatic to severe disease. HHV-6B causes exanthem subitum. The virus can be recovered from peripheral blood mononuclear cells during the acute phase of exanthem subitum, but the host remains latently infected throughout life. In immunocompromised patients undergoing kidney, liver, or bone marrow transplantation latent HHV-6B is reactivated, at times causing severe or fatal disease. Here, we describe the establishment of an in vitro system for reactivation of HHV-6B and HHV-7 from latency. HHV-7 is reactivated from latently infected peripheral blood mononuclear cells by T-cell activation. HHV-6B could not be reactivated under similar conditions; however, the latent HHV-6B could be recovered after the cells were infected with HHV-7. Once reactivated, the HHV-6B genomes became prominent and the HHV-7 disappeared. We conclude that HHV-7 can provide a transacting function(s) mediating HHV-6 reactivating from latency. Understanding the activation process is critical for the development of treatments to control the activation of latent viruses so as to avoid these sometimes life threatening infections in transplant recipients.

Exanthem subitum (roseola infantum) with vesicular lesions

We report a 7-month-old boy who developed vesicular lesions during the course of exanthem subitum. Human herpesvirus-6 (HHV-6) DNA was detected both in the skin lesions and in the throat, by polymerase chain reaction. IgG and IgM antibodies against HHV-6 were 1:10 and < 1:10, respectively on the tenth day of the illness, and > 1:640 and 1:10 on the twenty-second day, respectively. These results suggest that this was primary HHV-6 infection.

Low-incidence latent infection with variant B or roseola type human herpesvirus 6 in leukocytes of healthy adults

Nested primer-based polymerase chain reaction was employed to determine the frequency of latent infection with human herpesvirus 6 (HHV-6) among healthy adults from Bratislava, Slovak Republic. A 592-bp region, upstream from the gene encoding the putative large tegument protein of HHV-6, was amplified from DNA extracted from peripheral blood mononuclear cells (PBMC) of only one of 29 seropositive adults, suggesting that as few as 1 in 10(5) PBMC may be infected with the virus. Direct sequencing of the 592-bp fragment indicated that the virus harbored by the seropositive Slovak subject (designated B38) differed by only 3 nucleotides from an HHV-6 variant B strain (R-147) isolated from an American infant with a roseola-like illness and by 32 bases from the variant A strain GS isolated from a patient with lymphadenopathy (5.4% sequence divergence). None of these strains had a deoxyadenosine at base position 1251, when compared to the published sequence of strain GS clone pZVH14. Although this discrepancy did not affect the large tegument protein gene, it altered the predicted amino acid sequences of two putative proteins coded by open-reading frames 1 and 2 (ORF 1 and ORF 2) located upstream from this gene.

Human herpesvirus-6 infection in children. A prospective study of complications and reactivation

BACKGROUND

Infection with human herpesvirus-6 (HHV-6) is nearly universal in infancy or early childhood. However, the course of this infection, its complications, and its potential for persistence or reactivation remain unclear.

METHODS

We studied infants and children under the age of three years who presented to our emergency department with acute illnesses. Infants and young children without acute illness were studied as controls. HHV-6 infection was identified by blood-mononuclear-cell culture, serologic testing, and the polymerase chain reaction (PCR).

RESULTS

No primary HHV-6 infection was found among 582 infants and young children with acute nonfebrile illnesses or among 352 controls without acute illness. Of 1653 infants and young children with acute febrile illnesses, 160 (9.7 percent) had primary HHV-6 infection, as documented by viremia and seroconversion. They ranged in age from 2 weeks to 25 months; 23 percent were under the age of 6 months. HHV-6 infections accounted for 20 percent of 365 visits to the emergency department for febrile illnesses among children 6 to 12 months old. Of the 160 infants and young children with acute HHV-6 infections, 21 (13 percent) were hospitalized, and 21 had seizures. Often the seizures appeared late and were prolonged or recurrent. HHV-6 infections accounted for one third of all febrile seizures in children up to the age of two years. In follow-up studies over a period of one to two years, the HHV-6 genome persisted in blood mononuclear cells after primary infection in 37 of 56 children (66 percent). Reactivation, sometimes with febrile illnesses, was suggested by subsequent increases in antibody titers in 16 percent (30 of 187) and by PCR in 6 percent (17 of 278). No recurrent viremia was detected. Of 41 healthy newborns studied, 12 (29 percent) had the HHV-6 genome in their blood mononuclear cells; nevertheless, 6 of these newborns subsequently had primary HHV-6 infections.

CONCLUSIONS

In infants and young children HHV-6 infection is a major cause of visits to the emergency department, febrile seizures, and hospitalizations. Perinatal transmission may occur, with possible asymptomatic, transient, or persistent neonatal infection.