HBLV (or HHV-6) in human cell lines

Identification of stimuli that enhance human herpesvirus 6A (HHV-6A) replication and reconstitution

Despite the availability of bacterial artificial chromosome (BAC) systems for human herpesvirus 6A (HHV-6A), reconstitution of infectious viruses is very challenging and time consuming. In this study, we developed approaches to improve the reconstitution process and enhance virus replication to overcome these technical challenges. Using dimethyl sulfoxide and exonuclease V, we significantly increased the efficiency of BAC transfections into JJHan T cells. We tested several stimulation strategies to enhance lytic replication and identified mitogens and glucocorticoids that, in combination, improve virus replication. In addition, we demonstrated that the interferon-mediated response impairs virus reconstitution and that the JAK1/JAK2 inhibitor ruxolitinib resulted in an immense improvement. Furthermore, hypoxia-inducible factor 1 alpha stabilization by IOX2 drastically accelerated virus reconstitution, indicating that the hypoxic response is a crucial regulator of HHV-6A replication. Our study sheds light on strategic approaches that improve replication and reconstitution of this ubiquitous human herpesvirus.

IMPORTANCE

HHV-6A is a betaherpesvirus that infects a wide range of human tissues and establishes lifelong latency in the host. Its reactivation has been implicated in several diseases, including multiple sclerosis, encephalitis, myocarditis, and chronic fatigue syndrome, although its pathogenetic role remains elusive. The efficacy of common antiviral drugs is limited, and no specific drugs target HHV-6A infection. The data of this study shed light on stimuli and potential pathways that influence HHV-6A replication and reconstitution. Our strategies not only simplify virus propagation and reconstitution to study HHV-6A biology but also provide the basis for the development of therapeutic strategies.

Symptomatic central nervous system tuberculosis and human herpesvirus-6 coinfection with associated hydrocephalus managed with endoscopic third ventriculostomy: A case report and review of human herpesvirus-6 neuropathology

Background

Human herpesvirus 6 (HHV-6) is a double-stranded DNA virus well established in the clinical literature to cause the near-universal childhood infection roseola infantum (exanthema subitum/sixth disease). Primary HHV-6 infection has been reported to cause meningoencephalitis in pediatric patients, although generally in the immunocompromised.

Case Description

The authors treated an immunocompetent 18-month-old female who transferred to our institution for a higher level of care given concerns for meningitis in the setting of decreased level of arousal (Glasgow Coma Scale 12), and bradycardia 9 days after the onset of nasal congestion, fatigue, and repeated bouts of emesis. Outside hospital cerebrospinal fluid (CSF) studies were notable for hypoglycorrhachia, elevated protein, elevated nucleated cells with a mononuclear predominance, and a meningitis polymerase chain reaction panel that was positive only for HHV-6. Brain magnetic resonance imaging with and without contrast revealed a basal cistern predominant leptomeningeal enhancement pattern as well as moderate ventriculomegaly with associated periventricular edema concerning acute communicating hydrocephalus. Considering the CSF studies, neuroimaging, and recent travel history to Mexico, central nervous system (CNS) tuberculosis (TB) was the leading suspicion, and antimicrobial therapy was initiated for this presumptive diagnosis with culture data only proving the TB suspicion correct after nearly 2 months in culture. Anti-viral therapy was initially not felt to be necessary as the HHV-6 was interpreted as incidental and not a cause of symptomatic meningitis in our immunocompetent host. The patient's hydrocephalus was treated with temporary CSF diversion followed by performance of an endoscopic third ventriculostomy. Despite appropriate hydrocephalus management, clinical improvement ultimately seemed to correlate with the initiation of antiviral therapy.

Conclusion

The authors present this case and review the literature on HHV-6-associated CNS infections with the goal of informing the neurosurgeon about this often clinically underestimated pathogen.

Transcriptomic profiling of thymic dysregulation and viral tropism after neonatal roseolovirus infection

Introduction

Herpesviruses, including the roseoloviruses, have been linked to autoimmune disease. The ubiquitous and chronic nature of these infections have made it difficult to establish a causal relationship between acute infection and subsequent development of autoimmunity. We have shown that murine roseolovirus (MRV), which is highly related to human roseoloviruses, induces thymic atrophy and disruption of central tolerance after neonatal infection. Moreover, neonatal MRV infection results in development of autoimmunity in adult mice, long after resolution of acute infection. This suggests that MRV induces durable immune dysregulation.

Methods

In the current studies, we utilized single-cell RNA sequencing (scRNAseq) to study the tropism of MRV in the thymus and determine cellular processes in the thymus that were disrupted by neonatal MRV infection. We then utilized tropism data to establish a cell culture system.

Results

Herein, we describe how MRV alters the thymic transcriptome during acute neonatal infection. We found that MRV infection resulted in major shifts in inflammatory, differentiation and cell cycle pathways in the infected thymus. We also observed shifts in the relative number of specific cell populations. Moreover, utilizing expression of late viral transcripts as a proxy of viral replication, we identified the cellular tropism of MRV in the thymus. This approach demonstrated that double negative, double positive, and CD4 single positive thymocytes, as well as medullary thymic epithelial cells were infected by MRV in vivo. Finally, by applying pseudotime analysis to viral transcripts, which we refer to as "pseudokinetics," we identified viral gene transcription patterns associated with specific cell types and infection status. We utilized this information to establish the first cell culture systems susceptible to MRV infection in vitro.

Conclusion

Our research provides the first complete picture of roseolovirus tropism in the thymus after neonatal infection. Additionally, we identified major transcriptomic alterations in cell populations in the thymus during acute neonatal MRV infection. These studies offer important insight into the early events that occur after neonatal MRV infection that disrupt central tolerance and promote autoimmune disease.

The Eruptive Fevers at Sixes and Sevens

Sixth Disease (roseola infantum) and its primary causative agent, HHV-6, share names that numerically concur. This article examines and answers the question of whether that correspondence is by design or coincidental by briefly reviewing the history and nomenclature of the HHV viruses and the classic febrile rashes of childhood while highlighting some clinical and microbiologic features of HHV-6 infection.

Human Herpesvirus 6 (HHV-6) Encephalitis in a Non-Transplant Patient With Polymyositis

Human herpesvirus 6 (HHV-6) was initially labeled as a human B lymphotropic virus because it was isolated in patients diagnosed with lymphoproliferative disorders. There are two variants of HHV-6: HHV-6A and HHV-6B. A considerable majority of recorded primary infections and reactivation events are primarily due to HHV-6B. We report a case of HHV-6 encephalitis reactivation in a 75-year-old Caucasian diabetic female with a past medical history of polymyositis treated with prednisone for a long time who presented with generalized weakness and drowsiness. She developed her symptoms after contact with her grandchildren, who recently had viral-like symptoms treated with antibiotics. Magnetic resonance imaging (MRI) of the brain without contrast showed 14 mm high transverse relaxation time (T2)/fluid-attenuated inversion recovery (FLAIR) signal intensity focus on the left temporal lobe, suspicious for primary versus metastatic neoplasm. Cerebrospinal fluid analysis found that protein concentration was 75 mg/dl, glucose concentration 55 mg/dl, white blood cell count was 22/mm3, with a lymphocytic predominance. Meningitis/encephalitis polymerase chain reaction (PCR) panel detected HHV-6. She was discharged after treatment with ganciclovir for 14 days. It is crucial to recognize HHV-6 infections in immunocompromised patients who present with a T2/FLAIR signal intensity focus in the left temporal lobe. In a hospital setting, rapid HHV-6 encephalitis testing is important to make a correct diagnosis to avoid any delay to prevent further morbidity and mortality.

The Presence of Human Herpesvirus 6 in the Brain in Health and Disease

The human herpesvirus 6 (HHV-6) -A and -B are two dsDNA beta-herpesviruses infectingalmost the entire worldwide population. These viruses have been implicated in multipleneurological conditions in individuals of various ages and immunological status, includingencephalitis, epilepsy, and febrile seizures. HHV-6s have also been suggested as playing a role inthe etiology of neurodegenerative diseases such as multiple sclerosis and Alzheimer's disease. Theapparent robustness of these suggested associations is contingent on the accuracy of HHV-6detection in the nervous system. The effort of more than three decades of researching HHV-6 in thebrain has yielded numerous observations, albeit using variable technical approaches in terms oftissue preservation, detection techniques, sample sizes, brain regions, and comorbidities. In thisreview, we aimed to summarize current knowledge about the entry routes and direct presence ofHHV-6 in the brain parenchyma at the level of DNA, RNA, proteins, and specific cell types, inhealthy subjects and in those with neurological conditions. We also discuss recent findings relatedto the presence of HHV-6 in the brains of patients with Alzheimer's disease in light of availableevidence.

The Not-So-Soft Spot: Pathophysiology of the Bulging Fontanelle in Association With Roseola

Roseola infantum is a clinical syndrome characterized by high fever followed by the emergence of a rash. Case reports have documented an association between bulging fontanelles and roseola. We propose a novel mechanism for the development of intracranial hypertension caused by human herpesvirus 6-induced cytokine elevation leading to increased cerebrospinal fluid production.

Human Herpes Virus 6 (HHV-6)-associated Lymphadenitis: Pitfalls in Diagnosis in Benign and Malignant Settings

Human herpes virus 6 (HHV-6) is a member of the β-herpesvirinae subfamily. Most people acquire HHV-6 primary infection early in life and reactivation may occur, most often in immunocompromised individuals, leading to various clinical manifestations. HHV-6 infected cells may be identified in lymph nodes in both reactive and neoplastic conditions. Cases were retrieved from the hematopathology consultation service archives at National Institutes of Health from 2003 to 2017 in which infection by HHV-6 had been documented by immunohistochemical stains to HHV-6 gp60/110 envelope glycoprotein. Five cases of reactive lymphadenitis and 3 cases of lymphoma; 2 angioimmunoblastic T-cell lymphoma and 1 classic Hodgkin lymphoma, positive for HHV-6 were identified. The reactive lymph nodes showed marked paracortical hyperplasia and admixed large atypical lymphoid cells exhibiting pleomorphic nuclei, vesicular chromatin, and prominent eosinophilic intranuclear inclusions. Vascular proliferation and necrosis were also present, raising suspicion of peripheral T-cell lymphoma. The 3 cases of lymphoma showed similar viral inclusions, in addition to the characteristic features diagnostic of the lymphoma. Staining for HHV-6 was positive with a membranous and Golgi pattern and was restricted to cells with evident inclusions on hematoxylin and eosin. HHV-6 infected cells were positive for CD3 and CD4. HHV-6 lymphadenitis can present with morphologic atypia creating a diagnostic pitfall for lymphoma. In such cases, careful attention to the characteristic viral inclusions can lead to immunohistochemical analysis highlighting the replicating virus. In cases of lymphoma, identification of the inclusions is key in detecting the associated infection as well as in avoiding misinterpretation of the lymphoma subtype.

Lymphoproliferative Syndromes Associated with Human Herpesvirus-6A and Human Herpesvirus-6B

Human herpesvirus 6A and 6B (HHV-6A and HHV-6B) have been noted since their discovery for their T-lymphotropism. Although it has proven difficult to determine the extent to which HHV-6A and HHV-6B are involved in the pathogenesis of many diseases, evidence suggests that primary infection and reactivation of both viruses may induce or contribute to the progression of several lymphoproliferative disorders, ranging from benign to malignant and including infectious mononucleosis-like illness, drug induced hypersensitivity syndrome/drug reaction with eosinophilia and systemic symptoms (DIHS/DRESS), and nodular sclerosis Hodgkin's lymphoma. Herein, we discuss the conditions associated with the lymphoproliferative capacity of HHV-6, as well as the potential mechanisms behind them. Continued exploration on this topic may add to our understanding of the interactions between HHV-6 and the immune system and may open the doors to more accurate diagnosis and treatment of certain lymphoproliferative disorders.

Structural and Ultrastructural Alterations in Human Olfactory Pathways and Possible Associations with Herpesvirus 6 Infection

Structural and ultrastructural alterations in human olfactory pathways and putative associations with human herpesvirus 6 (HHV-6) infection were studied. The olfactory bulb/tract samples from 20 subjects with an unspecified encephalopathy determined by pathomorphological examination of the brain autopsy, 17 healthy age-matched and 16 younger controls were used. HHV-6 DNA was detected in 60, 29, and 19% of cases in these groups, respectively. In the whole encephalopathy group, significantly more HHV-6 positive neurons and oligodendrocytes were found in the gray matter, whereas, significantly more HHV-6 positive astrocytes, oligodendrocytes, microglia/macrophages and endothelial cells were found in the white matter. Additionally, significantly more HHV-6 positive astrocytes and, in particular, oligodendrocytes were found in the white matter when compared to the gray matter. Furthermore, when only HHV-6 PCR⁺ encephalopathy cases were studied, we observed similar but stronger associations between HHV-6 positive oligodendrocytes and CD68 positive cells in the white matter. Cellular alterations were additionally evidenced by anti-S100 immunostaining, demonstrating a significantly higher number of S100 positive cells in the gray matter of the whole encephalopathy group when compared to the young controls, and in the white matter when compared to both control groups. In spite the decreased S100 expression in the PCR⁺ encephalopathy group when compared to PCR^- cases and controls, groups demonstrated significantly higher number of S100 positive cells in the white compared to the gray matter. Ultrastructural changes confirming the damage of myelin included irregularity of membranes and ballooning of paranodal loops. This study shows that among the cellular targets of the nervous system, HHV-6 most severely affects oligodendrocytes and the myelin made by them.

Reactivation of Human Herpes Virus-6 After Pediatric Stem Cell Transplantation: Risk Factors, Onset, Clinical Symptoms and Association With Severity of Acute Graft-Versus-Host Disease

BACKGROUND AND METHODS

To study clinical symptoms, timing and consequences of human herpesvirus-6 (HHV-6) reactivation after pediatric allogeneic stem cell transplantation (SCT), HHV-6 was investigated by plasma polymerase chain reaction in a cohort of 106 pediatric SCT recipients.

RESULTS

HHV-6 viremia was detected post-SCT in 48% of the patients with a median time of onset at 20 days after SCT. In week 3 and 4 post-SCT, HHV-6 is the most common infectious agent detected. In up to 30% of the patients with fever of unknown origin, HHV-6 was the only detected infectious agent to explain fever. Patients transplanted with an unrelated donor or receiving serotherapy were at increased risk of HHV-6 reactivation. The onset of HHV-6 reactivation coincided with the appearance of lymphocytes and monocytes in peripheral blood. Treatment with alemtuzumab (MabCampath) delayed both lymphocyte and monocyte engraftment and, concomitantly, onset of HHV-6 reactivation was delayed in those cases. HHV-6 reactivation was not associated with an increased incidence of acute graft-versus-host disease (GvHD). However, progression to grade II-IV GvHD was in 9 of 10 patients associated with HHV-6 reactivation before GvHD (P = 0.006) and HHV-6 was the only infection with such an association.

CONCLUSIONS

HHV-6 frequently reactivates after pediatric SCT around the time of mononuclear cell engraftment and is associated with an increased severity of GvHD. HHV-6 may explain fever of unknown origin in 30% of the patients early after SCT. Assessment of HHV-6 reactivation in patients early after SCT can be instrumental for clinical decision making.

Laboratory and clinical aspects of human herpesvirus 6 infections

Human herpesvirus 6 (HHV-6) is a widespread betaherpesvirus which is genetically related to human cytomegalovirus (HCMV) and now encompasses two different species: HHV-6A and HHV-6B. HHV-6 exhibits a wide cell tropism in vivo and, like other herpesviruses, induces a lifelong latent infection in humans. As a noticeable difference with respect to other human herpesviruses, genomic HHV-6 DNA is covalently integrated into the subtelomeric region of cell chromosomes (ciHHV-6) in about 1% of the general population. Although it is infrequent, this may be a confounding factor for the diagnosis of active viral infection. The diagnosis of HHV-6 infection is performed by both serologic and direct methods. The most prominent technique is the quantification of viral DNA in blood, other body fluids, and organs by means of real-time PCR. Many active HHV-6 infections, corresponding to primary infections, reactivations, or exogenous reinfections, are asymptomatic. However, the virus may be the cause of serious diseases, particularly in immunocompromised individuals. As emblematic examples of HHV-6 pathogenicity, exanthema subitum, a benign disease of infancy, is associated with primary infection, whereas further virus reactivations can induce severe encephalitis cases, particularly in hematopoietic stem cell transplant recipients. Generally speaking, the formal demonstration of the causative role of HHV-6 in many acute and chronic human diseases is difficult due to the ubiquitous nature of the virus, chronicity of infection, existence of two distinct species, and limitations of current investigational tools. The antiviral compounds ganciclovir, foscarnet, and cidofovir are effective against active HHV-6 infections, but the indications for treatment, as well as the conditions of drug administration, are not formally approved to date. There are still numerous pending questions about HHV-6 which should stimulate future research works on the pathophysiology, diagnosis, and therapy of this remarkable human virus.

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.

Herpesvirus-associated acute urticaria: an age matched case-control study

Background

Acute and recurrent acute urticaria are often associated with multiple factors including infections and recent data suggest a role for herpesviruses.

Objective

To test the null hypothesis, that is, there is no association of herpesvirus infections with urticaria.

Methods

Thirty-seven patients between one month and 15 years of age were age matched to 37 controls who were healthy or had mild acute respiratory infections but without urticaria. Patients and controls were followed for 1 to 6 years. Diagnostic studies included DNA detection by real-time PCR for herpes simplex virus (HSV) types 1 and 2, Epstein-Barr virus (EBV), cytomegalovirus (CMV) and human herpesvirus-6 (HHV-6). Tests for other infections included adenovirus, parvovirus B 19, respiratory syncytial virus, influenza A, Group A streptococci, rotavirus, and parasites.

Results

Specific infections were diagnosed in 26 of 37 cases and among 9 of 37 control children (P=0.0002). Single or concomitant herpesvirus infections occurred in 24 cases and in 4 controls (65% vs 11 %, p=0.0003). Cases had 10 HHV-6 infections, 8 CMV infections, 5 EBV infections, and 4 HSV-1 infections.

Conclusion

Herpesvirus infections are associated with acute or recurrent acute urticaria.

Ganciclovir-resistant human herpesvirus-6 encephalitis in a liver transplant patient: a case report

Human herpesvirus-6 (HHV-6) was initially isolated in 1986 from patients with lymphoproliferative disorders (Ablashi et al. 1987). Since that time, two genetically distinct variants were sequenced, HHV-6A and HHV-6B (Ablashi and Balachandran 1991). Both variants have been linked with neurologic disease (Crawford et al. 2007). HHV-6 encephalitis has been well described in literature, typically presenting with confusion, coma, seizure, and headache. The majority of HHV-6 encephalitis has been limited to post-transplant recipients (Singh and Paterson 2000). Encephalitis due to HHV-6 infection has been reported in two liver transplant recipients (Massih and Razonable 2009 and Montejo et al. 2002). Although there has been in vitro studies regarding the potential resistance patterns for HHV-6 virus, there has been only one clinic case report supporting these findings (Isegawa et al. 2009). We describe the first case of ganciclovir-resistant HHV-6 encephalitis in a post-liver transplant patient.

Presence of human herpes virus 6 (HHV6) in pediatric lymphomas: impact on clinical course and association with cytomegalovirus infection

Background

Activation of herpes virus 6 (HHV6) has seen in Hodgkin's and non-Hodgkin's Lymphoma (HL&NHL) as a result of lymphoma associated immunosuppression. Multiple studies have suggested an association between both HHV6 and cytomegalovirus CMV for development of CMV disease affecting the pathogenesis of lymphoma. Therefore, this study investigated the frequency of HHV6, its impact on clinical manifestations of lymphoma and its possible association with risk for development of CMV infection in pediatric lymphoma patients.

Methods

Presence of HHV6 DNA and CMV DNA was investigated by PCR assay in both WBC's and plasma samples from 50 patients diagnosed with HL or NHL. CMV antibody titer was also determined in sera obtained from each patient. Twenty apparently healthy siblings were used as a control group.

Results

In a study group of 50 patients diagnosed with HL or NHL, 23/50 (46%) were found to be positive for herpes virus DNA (HHV6 or CMV) in WBC's or plasma by PCR assay and this was significantly higher than its presence in the pediatric control group 2/20 (10%) (p = 0.005). Ten out of these 23 (43%) were found to have active CMV infection. Fifty six percent of patients with CMV infection were found among NHL cases with B- subtype. The presence of both herpes viruses DNA was significantly associated with more frequent episodes of febrile neutropenia (median 3 episodes), absolute neutrophil count (< 0.8), lymphocytes (< 0.5), and low hemoglobin level (< 9.1), (p < 0.05).

Conclusion

The presence of HHV6 can be considered as a predicting indicator of cellular immunosuppression preceding the onset of CMV infection which may result in a severe outcome among pediatric lymphoma patients.

Lymphotropic herpes virus (EBV, HHV-6, HHV-8) DNA sequences in HIV negative Castleman's disease

Aim-To evaluate the possible involvement of lymphotropic herpes viruses in Castleman's disease.Methods-Archival formalin fixed, paraffin wax embedded biopsy specimens from 16 HIV negative patients (11 with localised and five of multicentric disease) were studied. Epstein-Barr virus (EBV), human herpes virus-6 (HHV-6) and human herpes virus-8 (HHV-8) DNA was detected using PCR. PCR was also used to characterise the EBV genomes and the clonal status of the lesions.Results-EBV sequences were identified in nine (56%) cases. The main EBV genotype detected was type 1. Two (12%) cases were positive for both HHV-6 and EBV sequences. HHV-8 sequences were detected in one case of localised Castleman's disease, the sequence of which differed from that of the HHV-8 prototype. No clonal immunoglobulin gene rearrangements were found.Conclusions-EBV DNA was detected in a substantial proportion of cases, suggesting that it may have a role in the pathogenesis of Castleman's disease, unlike HHV-6 which was detected rarely. This is the first report of HHV-8 specific sequences in the localised from of the disease.

High-level human herpesvirus-6 viremia associated with onset of Stevens-Johnson syndrome: report of two cases

The pathogenesis of Stevens-Johnson syndrome (SJS) remains obscure, but it has been associated with various infectious agents, including members of the herpesvirus family. We present the first report of high-level human herpesvirus-6 viremia at the onset of SJS, suggesting a possible new association. This finding supports the need for further investigation into the possible relationship between human herpesvirus-6 and SJS, which may illuminate the pathogenesis of SJS and bring us closer to achieving enhanced prevention and treatment of this rare disease.

The U24 protein from human herpesvirus 6 and 7 affects endocytic recycling

Modulation of T-cell receptor expression and signaling is essential to the survival of many viruses. The U24 protein expressed by human herpesvirus 6A, a ubiquitous human pathogen, has been previously shown to downregulate the T-cell receptor. Here, we show that U24 also mediates cell surface downregulation of a canonical early endosomal recycling receptor, the transferrin receptor, indicating that this viral protein acts by blocking early endosomal recycling. We present evidence that U24 is a C-tail-anchored protein that is dependent for its function on TRC40/Asna-1, a component of a posttranslational membrane insertion pathway. Finally, we find that U24 proteins from other roseoloviruses have a similar genetic organization and a conserved function that is dependent on a proline-rich motif. Inhibition of a basic cellular process by U24 has interesting implications not only for the pathogenicity of roseoloviruses but also for our understanding of the biology of endosomal transport.

Fatal HHV6 infection in an immunocompromised patient presenting with skin involvement

Infection with human herpesvirus-6 (HHV6) has a broad distribution in the human population, with a seroprevalence approaching 100% worldwide. Primary infection takes place during childhood, after which the virus remains latent mostly in lymphocytes and monocytes at various sites. Immunosuppression can result in viral reactivation, associated with clinical sequelae and even death. We report a case of a disseminated HHV6 infection in a 53-year-old patient, who was immunocompromised after allogeneic bone marrow transplant treatment for acute lymphocytic leukemia. Initially, he presented with a macular eruption of the skin, followed by involvement of other sites. Histopathologic analysis of skin biopsies revealed superficial perivascular large atypical mononuclear cells with intranuclear and intracytoplasmic inclusions. Most affected cells labeled with antibodies to CD3 and CD43 as lymphocytes, and some labeled with CD68 as macrophages. Polymerase chain reaction (PCR) studies of the blood, skin, liver, colon, cerebrospinal fluid and brain were positive for HHV6 virus. Additionally, the serologic titers for HHV6 were high. Viral particles were also detected by electron microscopy (EM) in the colon. Although rare, HHV6 virus may be an important pathogen in immunocompromised patients, and may present initially in the skin. Awareness of this infection is critical to diagnosis in acute settings.

Detection of human herpesvirus-6 in cerebrospinal fluid of patients with encephalitis

OBJECTIVE

Virus infections are the most common causes of encephalitis, a syndrome characterized by acute inflammation of the brain. More than 150 different viruses have been implicated in the pathogenesis of encephalitis; however, because of limitations with diagnostic testing, causative factors of more than half of the cases remain unknown.

METHODS

To investigate whether human herpesvirus-6 (HHV-6) is a causative agent of encephalitis, we examined for evidence of virus infection by determining the presence of viral sequence using polymerase chain reaction and assessed HHV-6 antibody reactivity in the cerebrospinal fluid of encephalitis patients with unknown cause. In a cohort study, we compared virus-specific antibody levels in cerebrospinal fluid samples of patients with encephalitis, relapsing-remitting multiple sclerosis, and other neurological diseases.

RESULTS

Our results demonstrated increased levels of HHV-6 IgG, as well as IgM levels, in a subset of encephalitis patients compared with other neurological diseases. Moreover, cell-free viral DNA that is indicative of active infection was detected in 40% (14/35) of encephalitis patients, whereas no amplifiable viral sequence was found in either relapsing-remitting MS or other neurological diseases patients. In addition, a significant correlation between polymerase chain reaction detection and anti-HHV-6 antibody response was also demonstrated.

INTERPRETATION

Collectively, these results suggested HHV-6 as a possible pathogen in a subset of encephalitis cases.

Evidence for human herpesvirus 6 variant A antibodies in multiple sclerosis: diagnostic and therapeutic implications

Human herpesvirus 6 (HHV-6) has been linked to the pathogenesis of multiple sclerosis (MS). HHV-6 antibodies in serum and cerebrospinal fluid (CSF) of 27 patients with clinically definite MS (CDMS) were compared with age- and sex-matched controls, including various other neurological diseases and symptoms (OND). In addition, we studied a series of 19 patients with clinically or laboratory supported possible MS (CPMS). Seroprevalence to HHV-6A was 100% in patients with MS, both in CDMS and CPMS, compared to 69.2% in patients with OND (P = .001 and .007). The mean immunoglobulin G (IgG) titers were significantly higher in patients with CDMS and CPMS than in controls (P = .005 and .00002). The proportion of acute primary infections without CSF involvement was similar in all groups; however, primary infections with intrathecal HHV-6 antibody production were more frequent in MS. In CSF, HHV-6A-specific antibodies were present in three (11.5%) and four (21.1%) patients with CDMS and CPMS, compared to none with OND (P = .06 and .01, respectively). Serological suggestions to HHV-6A infection occurred more often in both CDMS and CPMS than in OND (14.8% versus 21.1% versus 3.8%). We conclude that a subpopulation of MS patients, and even a greater proportion of possible MS subjects, has serological evidence of HHV-6A infection, which might provide new markers for diagnosis and therapy.

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

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

Phenotypic alterations and survival of monocytes following infection by human herpesvirus-6

Freshly isolated monocytes rapidly undergo physiological changes in vitro, resulting in programmed cell death (apoptosis). Activation of monocytes, which promotes differentiation into macrophages, is known to inhibit apoptotic processes. In the present study, we report that human herpesvirus-6 (HHV-6) prevents monocytes from undergoing spontaneous apoptosis during the first 72 hours of culture. Furthermore, significant alterations in cell-surface phenotype were observed after 72 hours of infection with HHV-6. HHV-6-infected monocyte cultures have considerably reduced levels of CD14, CD64 (FcgammaRI) and HLA-DR antigen on their surface, while CD32 (FcgammaRII) expression is unaffected. On the basis of these results, we hypothesize that HHV-6 promotes monocytes survival and causes phenotypic modifications that could favor immune evasion and ensure its persistence within the infected host.

Comparison of the SYBR Green and the hybridization probe format for real-time PCR detection of HHV-6

A comparative study was conducted of a novel real-time quantitative PCR test (LightCycler System) with FastStart DNA Master(PLUS) SYBR Green I dye to detect DNA of human herpes virus 6 (HHV-6). Results were compared with those of a real-time quantitative PCR with hybridization probe (HP) formats using the fluorescence resonance energy transfer method, and with those of a single qualitative PCR test. The detection limit of the test with SYBR Green I dye was 20 copies of the virus, similar to that of the other two tests. The reproducibility was satisfactory. The new test has the same advantages as real-time PCR with HP formats and offers a greater versatility at lower cost.

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

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

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

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

Activation of monocyte cyclooxygenase-2 gene expression by human herpesvirus 6. Role for cyclic AMP-responsive element-binding protein and activator protein-1

Prostaglandin E(2) (PGE(2)) is an arachidonic acid metabolite mainly produced by activated monocytes/macrophages (Mo/Mphi) that display broad immunomodulatory activities. Several viruses capable of infecting Mo/Mphi modulate PGE(2) synthesis in a way that favors the infection processes and the spread of virions. In the present work, we studied the effect of human herpesvirus 6 (HHV-6) infection of Mo/Mphi on PGE(2) synthesis. Our results indicate that HHV-6 induces COX-2 gene expression and PGE(2) synthesis within a few hours of infection. We mapped the different promoter elements associated with COX-2 gene activation by HHV-6 to two cis-acting elements: a cyclic AMP-responsive element and an activator protein-1 element. HHV-6 immediate-early protein 2 was identified as a modulator of COX-2 gene expression in Mo/Mphi. Finally, addition of PGE(2) to HHV-6-infected peripheral blood mononuclear cells cultures was found to increase significantly viral replication. Overall, these results further contribute to the immunomodulatory properties of HHV-6 and highlight a potential role for eicosanoids in the replication process of this virus.

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

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

T-tropic human immunodeficiency virus (HIV) type 1 Nef protein enters human monocyte-macrophages and induces resistance to HIV replication: a possible mechanism of HIV T-tropic emergence in AIDS

Increasing interest has been devoted to the role that monocyte-macrophages play in the pathogenesis of AIDS. The hypothesis of an involvement in AIDS pathogenesis of human/simian immunodeficiency virus (HIV/SIV) Nef also is currently under evaluation by many investigators. The original basis of this hypothesis came from evidence that monkeys infected with a nef-deleted SIV strain failed to develop simian AIDS. Here, we show that treatment of human monocyte-derived macrophages (MDM) with recombinant HIV-1 Nef protein (rNef) induces a strong inhibition of the replication of either macrophage (M-) or dual-tropic HIV-1 strains. Through cytofluorimetric analyses, we detected internalization of FITC-conjugated rNef in MDM as early as 6 h after treatment. Confocal microscope observations demonstrated that the intracellular distribution of internalized rNef was identical to that of endogenously produced Nef. Down-regulation of the CD4 HIV receptor detected upon rNef treatment of MDM suggested that the rNef-induced HIV inhibition occurred at the virus entry step. This deduction was strengthened by the observation that CD4-independent infection was totally insensitive to rNef treatment. The specificity of all observed effects was demonstrated by immunodepletion of rNef. Finally, we showed that the resistance to HIV replication induced by rNef treatment in MDM favours the spread of T-tropic over M-tropic HIV strains in doubly infected CD4(+) lymphocyte-MDM co-cultures. We propose that extracellular Nef contributes to AIDS pathogenesis by inducing resistance to M-tropic HIV replication in MDM, thereby facilitating the switching from M- to T-tropic HIV prevalence that correlates frequently with AIDS progression.

Susceptibility of human herpesvirus 6 to antiviral compounds by flow cytometry analysis

BACKGROUND

The emergence of human herpesvirus 6 (HHV-6) as a human pathogen led to the possibility of specific therapy against HHV-6 and the development of standardized susceptibility assays of HHV-6 to antivirals.

METHODS

We have developed a flow cytometry method to analyze the multiplication of the HST strain of human herpesvirus 6 (HHV-6) variant B in vitro using monoclonal antibodies specific to virus proteins. This method was subsequently used to determine the sensitivity of HST multiplication in MT4 cells to four antiviral compounds of three different classes: acyclovir (ACV) and ganciclovir (GCV), two acyclic guanosine analogs; cedofovir (CDV), an acyclic nucleoside phosphonate; and phosphonoformic acid (PFA), a pyrophosphate analog.

RESULTS

The 50% inhibitory concentrations (IC(50)) of ACV, GCV, CDV, and PFA determined by flow cytometry assay were 25.3, 6.4, 0.95, and 6.0 microM, respectively (5.7, 1.6, 0.3, and 1.8 microg/ml, respectively). These data together with the results of cytotoxicity assays confirmed the high efficiency and selectivity of CDV and PFA against HHV-6 B in vitro, suggested by previous results.

CONCLUSIONS

Our flow cytometric assay appeared as a reproducible specific method to characterize HHV-6 susceptibility to antiviral compounds. It can be considered as a convenient alternative to the other immunologic and DNA hybridization assays used for that purpose.

Human herpesvirus 6

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

Human cytomegalovirus and human herpesvirus 6 genes that transform and transactivate

This review is an update on the transforming genes of human cytomegalovirus (HCMV) and human herpesvirus 6 (HHV-6). Both viruses have been implicated in the etiology of several human cancers. In particular, HCMV has been associated with cervical carcinoma and adenocarcinomas of the prostate and colon. In vitro transformation studies have established three HCMV morphologic transforming regions (mtr), i.e., mtrI, mtrII, and mtrIII. Of these, only mtrII (UL111A) is retained and expressed in both transformed and tumor-derived cells. The transforming and tumorigenic activities of the mtrII oncogene were localized to an open reading frame (ORF) encoding a 79-amino-acid (aa) protein. Furthermore, mtrII protein bound to the tumor suppressor protein p53 and inhibited its ability to transactivate a p53-responsive promoter. In additional studies, the HCMV immediate-early protein IE86 (IE2; UL122) was found to interact with cell cycle-regulatory proteins such as p53 and Rb. However, IE86 exhibited transforming activity in vitro only in cooperation with adenovirus E1A. HHV-6 is a T-cell-tropic virus associated with AIDS-related and other lymphoid malignancies. In vitro studies identified three transforming fragments, i.e., SalI-L, ZVB70, and ZVH14. Of these, only SalI-L (DR7) was retained in transformed and tumor-derived cells. The transforming and tumorigenic activities of SalI-L have been localized to a 357-aa ORF-1 protein. The ORF-1 protein was expressed in transformed cells and, like HCMV mtrII, bound to p53 and inhibited its ability to transactivate a p53-responsive promoter. HHV-6 has also been proposed to be a cofactor in AIDS because both HHV-6 and human immunodeficiency virus type 1 (HIV-1) have been demonstrated to coinfect human CD4(+) T cells, causing accelerated cytopathic effects. Interestingly, like the transforming proteins of DNA tumor viruses such as simian virus 40 and adenovirus, ORF-1 was also a transactivator and specifically up-regulated the HIV-1 long terminal repeat when cotransfected into CD4(+) T cells. Finally, based on the interactions of HCMV and HHV-6 transforming proteins with tumor suppressor proteins, a scheme is proposed for their role in oncogenesis.

The U69 gene of human herpesvirus 6 encodes a protein kinase which can confer ganciclovir sensitivity to baculoviruses

The protein encoded by the U69 open reading frame (ORF) of human herpesvirus 6 (HHV-6) has been predicted to be a protein kinase. To investigate its functional properties, we have expressed the U69 ORFs from both HHV-6 variants, A and B, by using recombinant baculoviruses (BV6AU69 and BV6BU69). Nickel agarose and antibody affinity chromatography was used to purify the proteins to homogeneity and when incubated with [gamma-32P]ATP, both U69 proteins became phosphorylated on predominantly serine residues. These data strongly suggest that U69 is a protein kinase which autophosphorylates. The phosphorylation reaction was optimal at physiological pH and low NaCl concentrations. It required the presence of Mg2+ or Mn2+, and Mg2+ was able to support phosphorylation over a wider range of concentrations than Mn2+. Both ATP and GTP could donate phosphate in the protein kinase assay and the former was more efficient. U69 was capable of phosphorylating histone and casein (serine/threonine kinase substrates) but not enolase (a tyrosine kinase substrate). For the autophosphorylation reaction, the Michaelis constants for ATP of baculovirus-expressed HHV-6A and HHV-6B U69 were calculated to be 44 and 11 microM, respectively. U69 is a homologue of the UL97 gene encoded by human cytomegalovirus which has been shown to phosphorylate the antiviral drug ganciclovir (GCV). We analyzed whether the U69 ORF alone was capable of conferring GCV sensitivity on baculoviruses BV6AU69 and BV6BU69. In plaque reduction experiments, these baculoviruses displayed a GCV-sensitive phenotype compared to a control baculovirus (BVLacZ). The 50% inhibitory concentrations (IC50) of BV6AU69 and BV6BU69 were calculated to be 0.35 and 0.26 mM, respectively, whereas the control baculovirus had an IC50 of >1.4 mM. This shows that the U69 gene product is the only one required to confer GCV sensitivity on baculovirus.

Human herpesvirus 6

Human herpesvirus (HHV) 6 is a beta-herpes, DNA virus. This virus shows closest homology with cytomegalovirus and HHV-7. Infection usually occurs in infants 6 to 24 months of age, and primary infection may result in roseola. HHV-6 infection in infants is the commonest cause of fever-induced seizures. Infection in adults is seen primarily in immunocompromised hosts with solid organ transplants or in those with human immunodeficiency virus infection. The virus is capable of pronounced interaction in vitro with cytomegalovirus and human immunodeficiency virus and induces immunosuppression and apoptosis. The importance of these interactions in vivo necessitates further investigation. HHV-6 infection may contribute to the pathogenesis of multiple sclerosis. HHV-6 may be diagnosed by viral culture, serology, or polymerase chain reaction.

Human herpesvirus 6: An emerging pathogen

Infections with human herpesvirus 6 (HHV-6), a beta-herpesvirus of which two variant groups (A and B) are recognized, is very common, approaching 100% in seroprevalence. Primary infection with HHV-6B causes roseola infantum or exanthem subitum, a common childhood disease that resolves spontaneously. After primary infection, the virus replicates in the salivary glands and is shed in saliva, the recognized route of transmission for variant B strains; it remains latent in lymphocytes and monocytes and persists at low levels in cells and tissues. Not usually associated with disease in the immunocompetent, HHV-6 infection is a major cause of opportunistic viral infections in the immunosuppressed, typically AIDS patients and transplant recipients, in whom HHV-6 infection/reactivation may culminate in rejection of transplanted organs and death. Other opportunistic viruses, human cytomegalovirus and HHV-7, also infect or reactivate in persons at risk. Another disease whose pathogenesis may be correlated with HHV-6 is multiple sclerosis. Data in favor of and against the correlation are discussed.

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.

Viruses and multiple sclerosis

Animal models illustrate how viruses and host genetic factors may interact to cause immune-mediated demyelination. Similar mechanisms may take place in at least some forms of multiple sclerosis, a disease that is histopathologically heterogeneous. No 'multiple sclerosis virus' has been found yet, although recent data on human herpesvirus-6 antigens in multiple sclerosis brain warrant further investigation. Multiple sclerosis associated retrovirus, a recently described retroviral sequence isolated from multiple sclerosis material, is a member of the endogenous retrovirus-9 family. The association between the expression of this virus associated retrovirus and multiple sclerosis is only tentative.

Studies on the antibodies to human herpesvirus type 6 among Hungarian patients with asymptomatic HIV infection

The occurrence and the possible role in promoting HIV infection by human herpesvirus type 6 (HHV-6) have not yet been revealed in Hungary. In different groups of patients, serum titre of IgM and IgG antibodies, as well as avidity of IgG were quantitated by indirect immunofluorescence and an enzyme-linked immunosorbent assay, using isolate U1102 of HHV-6 variant A as antigen. In 60% of HIV-seronegative adult controls, high avidity IgG antibodies were found in low titre suggesting childhood infection. In HIV-seronegative persons with high risk behaviour for HIV-infection, both IgM and low avidity IgG were frequently found in higher titre, representing either primary or frequent reinfections, or reactivation of latent HHV-6. In asymptomatic HIV-seropositive patients, high titre of high avidity IgG antibodies was predominant, proving virus infection in the near past. These results indicate the contribution of HHV-6 to immunosuppression prior to AIDS, predisposing the organism to HIV infection.

Human herpesvirus-6 infection in liver transplant recipients: documentation of pathogenicity

BACKGROUND

The new herpesvirus, human herpesvirus-6 (HHV-6), is able to cause clinical illness after transplantation; however, the pathogenic potential and the clinical features of HHV-6 have not been defined in liver transplant recipients.

METHODS

We report the first cases of invasive and symptomatic infection due to HHV-6 in liver transplant recipients.

RESULTS

HHV-6 infection occurred in four liver transplant recipients at a median of 50 days after transplant (range 17-90 days). Severe cytopenia was observed in all patients; leukopenia (with median leukocyte count of 1400/mm3) was the most commonly effected bone marrow lineage. One of the four patients had interstitial pneumonitis due to HHV-6. No other virus (e.g., cytomegalovirus) or another pathogen was detected in the lungs, blood, or bone marrow in any of the above patients.

CONCLUSIONS

Our data suggest that HHV-6 can be a pathogen in liver transplant recipients; idiopathic bone marrow suppression is its predominant clinical sequelae. Recognition of HHV-6 infection is clinically pertinent because HHV-6 is potentially treatable with the currently available antiviral agents.

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.

Induction of T-cell apoptosis by human herpesvirus 6

The mechanisms of cell death in CD4+ T cells mediated by human herpesvirus 6 (HHV-6) were investigated. The frequency of cell death in the human CD4+ T-cell line JJHAN, which had been inoculated with HHV-6 variant A or B, appeared to be augmented by tumor necrosis factor alpha (TNF-alpha). Agarose gel electrophoresis of DNA from HHV-6-inoculated cells showed DNA fragmentation in multiples of the oligonucleosome length unit. The degree of DNA fragmentation increased when HHV-6-inoculated cells were cultured in the presence of TNF-alpha. Flow cytometry and Scatchard analysis of TNF receptors revealed an increase in the number of the p55 form of TNF receptors on JJHAN cells after HHV-6 inoculation. It also appeared that treatment with anti-Fas monoclonal antibody (MAb) induced marked apoptosis in HHV-6-inoculated cells. Transmission electron microscopy showed characteristics of apoptosis, such as chromatin condensation and fragmentation of nuclei, but virus particles were hardly detected in apoptotic cells. Two-color flow cytometric analysis using anti-HHV-6 MAb and propidium iodide revealed that DNA fragmentation was present predominantly in uninfected cells but not in productively HHV-6-infected cells. In addition, JJHAN cells incubated with UV light-irradiated and ultracentrifuged culture supernatant of HHV-6-infected cells appeared to undergo apoptosis. The present study demonstrated that both HHV-6 variants A and B induce apoptosis in CD4+ T cells by indirect mechanisms, as reported recently in human immunodeficiency virus type 1 infection.

Development and application of HHV-6 antigen capture assay for the detection of HHV-6 infections

An HHV-6 antigen capture assay measuring gp116/64/54 antigen was developed. This ELISA is specific for HHV-6 Variants A and B, does not cross react with other human herpesviruses, is sensitive, stable, quantitative, and can detect antigen in body fluids and cell cultures. Relative to virus isolation or techniques for measuring HHV-6 nucleic acids, the assay is much simpler and less expensive to perform. Plasmas/sera (413) obtained from healthy donors, children with Exanthem subitum, febrile illnesses, patients with Chronic Fatigue Syndrome, and AIDS patients tested by antigen capture assay demonstrated that the assay is useful in clinical laboratory settings. The capture assay can also be used to monitor cell cultures for virus isolation, production, quantitation, and antiviral agent screening.

Human herpesvirus-6 infections

HHV-6 is ubiquitous in the community, appears to be acquired early in life, and has been proved to cause the clinical syndrome of exanthem subitum, and rarely to cause encephalitis. Like other herpesviruses, HHV-6 is capable of establishing latent infection and reactivating under a variety of stimuli. Improved diagnostic techniques have led to increased recognition of HHV-6 in the presence of many diseases, but much of the evidence for an aetiological role is inconclusive. There is accruing evidence for possible pathological roles in the immunocompromised host, but the evidence is less convincing for the range of associations otherwise listed for the normal host at the present time.

On the role of human herpesvirus 6 in viral latency in nervous tissue and in cerebral lymphoma

Latent infections by human herpesvirus 6 (HHV6) in nervous tissue and its role in human disease are poorly understood. For the present study, an improved PCR method has been applied to brain tissue samples from 5 different brain regions from 20 forensic post-mortem cases without neurologic involvement. Spleen tissue from these cases as well as 5 cerebral lymphoma tissue samples were also examined. HHV6 DNA was detected in 3 of 20 brains. The viral sequences could be amplified from cortical brain tissue from these 3 cases. In one of these cases, HHV6 DNA was detectable in two separate tissue samples. PCR was negative in brain lymphoma and spleen tissue. These findings point toward HHV6 latency in brain tissue and might thus support the reported glial tropism of this virus. No role could be found for HHV6 in the pathogenesis of cerebral lymphoma.