Human Herpesvirus 6 Variant Research Articles

Presence of cytomegalovirus and human herpesvirus 6 in-patients with lymphomas

Background: Cytomegalovirus (CMV) and human herpesvirus 6 (HHV-6) remain latent after primary infection and can be reactivated after immunosuppression. Very little is known about the prevalence of these herpes viruses in lymphomas patients following cytotoxic chemotherapy in the absence of allogeneic transplantation. Therefore, this study investigated the frequency of HHV-6, its impact on clinical manifestations and its possible association with the risk of development of CMV infection in Hodgkin's and non-Hodgkin's Lymphoma (HL &NHL). Methods and materials: This study included 62 patients with lymphomas (25 HL and 37 NHL) diagnosed and treated in the hematology department of Farhat Hached Hospital in Sousse (Tunisia) during the period from June 2015 to July 2018. One hundred and twenty-four healthy individuals were used as age and sex-matched control group. Herpesviruses DNA (HHV6 and/or CMV) were detected by multiplex polymerase chain reaction (PCR). Nested PCR was used to discern HHV-6 variants A and B for each HHV6 positive sample. Results: Herpesviruses DNA (HHV6 and/or CMV) was present in 12 of the 62 patients with lymphomas (19.35%), a frequency that was significantly higher than that in the control group (4/124, 3.2%) (p < 0.01).There was no significant difference between HL or NHL groups regarding the presence of HHV6 and or CMV (p = 0.74). The CMV DNA was identified in eight patients (1HL, 7NHL) while in 4 both CMV and HHV-6(3HL, 1NHL).CMV infection was associated with a significantly higher rate of HHV6 infection (p < 0.01). Variant B was found in 2 HL patients and variant B in 2 NHL while all the control group individuals showed positive for HHV-6 variant B. Ten out of twelve infected patients were symptomatic with fever and pneumonia (60%), lymphopenia (<500/μL) (30%), diarrhea (20%), hepatitis (10%). The presence of both herpes viruses DNA was not significantly associated with more frequent symptomatic infection (100% vs. 75%, p = 0.5). Conclusion: The detection of CMV and/or HHV6 were more commonly observed in patients with lymphomas and HHV-6 infection was often revealed with CMV infection. In the future, enhanced prospective surveillance may help shed more light on the clinical significance of these herpes virus infections in patients with lymphomas.

Endogenization and excision of human herpesvirus 6 in human genomes.

Sequences homologous to human herpesvirus 6 (HHV-6) are integrated within the nuclear genome of about 1% of humans, but it is not clear how this came about. It is also uncertain whether integrated HHV-6 can reactivate into an infectious virus. HHV-6 integrates into telomeres, and this has recently been associated with polymorphisms affecting MOV10L1. MOV10L1 is located on the subtelomere of chromosome 22q (chr22q) and is required to make PIWI-interacting RNAs (piRNAs). As piRNAs block germline integration of transposons, piRNA-mediated repression of HHV-6 integration has been proposed to explain this association. In vitro, recombination of the HHV-6 genome along its terminal direct repeats (DRs) leads to excision from the telomere and viral reactivation, but the expected “solo-DR scar” has not been described in vivo. Here we screened for integrated HHV-6 in 7,485 Japanese subjects using whole-genome sequencing (WGS). Integrated HHV-6 was associated with polymorphisms on chr22q. However, in contrast to prior work, we find that the reported MOV10L1 polymorphism is physically linked to an ancient endogenous HHV-6A variant integrated into the telomere of chr22q in East Asians. Unexpectedly, an HHV-6B variant has also endogenized in chr22q; two endogenous HHV-6 variants at this locus thus account for 72% of all integrated HHV-6 in Japan. We also report human genomes carrying only one portion of the HHV-6B genome, a solo-DR, supporting in vivo excision and possible viral reactivation. Together these results explain the recently-reported association between integrated HHV-6 and MOV10L1/piRNAs, suggest potential exaptation of HHV-6 in its coevolution with human chr22q, and clarify the evolution and risk of reactivation of the only intact (non-retro)viral genome known to be present in human germlines.

Detection frequency of human herpesviruses-6A, -6B, and -7 genomic sequences in central nervous system DNA samples from post-mortem individuals with unspecified encephalopathy.

In this autopsy-based study, human herpesvirus-6 (HHV-6) and -7 (HHV-7) genomic sequence frequency, HHV-6 variants, HHV-6 load and the expression of HHV-6 antigens in brain samples from the individuals, with and without unspecified encephalopathy (controls), using nested and real-time polymerase chain reactions, restriction endonuclease, and immunohistochemical analysis were examined. GraphPad Prism 6.0 Mann-Whitney nonparametric and chi-square test and Fisher's exact test were used for statistical analysis. The encephalopathy diagnoses were shown by magnetic resonance imaging made during their lifetime and macro- and microscopically studied autopsy tissue materials. Widespread HHV-6 and/or HHV-7 positivity was detected in the brain tissue of various individuals with encephalopathy, as well as in controls (51/57, 89.4% and 35/51, 68.6%, respectively; p = 0.009). Significantly higher detection frequency of single HHV-6 and concurrent HHV-6 + HHV-7 DNA was found in pia mater meninges, frontal lobe, temporal lobe, and olfactory tract DNAs in individuals with encephalopathy compared to the control group. HHV-6 load and higher frequency of the viral load >10 copies/10(6) cells significantly differed in samples from individuals with and without encephalopathy. The expression of HHV-6 antigens was revealed in different neural cell types with strong predominance in the encephalopathy group. In all HHV-6-positive autopsy samples of individuals with and without encephalopathy, HHV-6B was revealed. Significantly higher detection frequency of beta-herpesvirus DNA, more often detected HHV-6 load >10 copies/10(6) cells, as well as the expression of HHV-6 antigens in different brain tissue samples from individuals with encephalopathy in comparison with control group indicate on potential involvement of these viruses in encephalopathy development.

Prevalence of Human Herpes Virus 6 (HHV-6) in Patients with Hemodialysis

HHV-6 is the causative agent of exanthema subitum in children. The main modes of transmission of HHV-6 arebody secretions such as infected saliva but it can be transmitted with blood and blood products that are infected with\the virus. Therefore, it is thought that the immunocompromised hemodialysis patients who had multiple bloodtransfusions due to various reasons, and who collectively use devices such as hemodialysis machines are at risk forHHV-6 infection. The present study aimed to determine the incidence of HHV-6 infection in hemodialysis patients. Twenty-five healthy individuals that were matched with 25 hemodialysis patients in terms of gender and age wereincluded in the study. The IgM and IgG sero-prevalence in the patient and control groups wereinvestigated with theindirect fluorescence antibody method and HHV-6 DNA prevalence and the determination of variant types (variant Aand variant B) were investigated with the PCR-RFLP molecular method. HHV-6 IgG and HHV-6 IgM antibodypositivity ratios in the patient and control groups were 76% and 20% respectively. Out of 50 serum samples of hemodialysis patients and healthy individuals, HHV-6 DNA was positive in seven of 25 samples of hemodialysispatients (28%) and it was positive in eight of 25 samples of the control group (32%). Variant analysis was performedwith the PCR-RFLP method in HHV-6 DNA positive hemodialysis patients and control patients. At the end of theanalysis, while variant A was not detected in the patient and control groups, variant B was detected in a total of 15individuals, including seven patients in the hemodialysis patient group and eight patients in the control group. Inconclusion, the researchers believe that there is a need for controlled studies including more samples to determinethe clinical importance of HHV-6 DNA and HHV-6 variants in hemodialysis patients.

Virologic and Immunologic Evidence Supporting an Association between HHV-6 and Hashimoto's Thyroiditis

Hashimoto's thyroiditis (HT) is the most common of all thyroid diseases and is characterized by abundant lymphocyte infiltrate and thyroid impairment, caused by various cell- and antibody-mediated immune processes. Viral infections have been suggested as possible environmental triggers, but conclusive data are not available. We analyzed the presence and transcriptional state of human herpesvirus 6 (HHV-6) in thyroid fine needle aspirates (FNA) and peripheral blood mononuclear cells (PBMCs) from 34 HT patients and 28 controls, showing that HHV-6 DNA prevalence (82% vs. 10%, p≤0.001) and viral load were significantly increased in FNA from HT patients, and thyrocytes from HT FNA displayed a 100-fold higher HHV-6 DNA load compared to infiltrating lymphocytes. In addition, while HHV-6 was strictly latent in positive samples from controls, a low grade acute infection was detected in HT samples. HHV-6 variant characterization was carried out in 10 HT FNA samples, determining that all specimens harbored HHV-6 Variant A.The tropism of HHV-6 for thyroid cells was verified by infection of Nthy-ori3-1, a thyroid follicular epithelial cell line, showing that thyrocytes are permissive to HHV-6 replication, which induces de novo expression of HLA class II antigens. Furthermore, HHV-6-infected Nthy-ori3-1 cells become targets for NK-mediated killing, NK cells from HT patients show a significantly more efficient killing of HHV-6 infected thyroid cells than healthy controls, and HT patients have increased T-cell responses to HHV-6 U94 protein, associated to viral latency. These observations suggest a potential role for HHV-6 (possibly variant A) in the development or triggering of HT.

Virological Analysis in Patients with Human Herpes Virus 6–Associated Ocular Inflammatory Disorders

To determine whether human herpes virus 6 (HHV-6) genomic DNA and mRNA can be detected in ocular samples from patients with inflammatory disorders, and whether viral replication is involved in the development of inflammation in the eye. After informed consent was obtained, ocular fluid samples (aqueous humor and vitreous fluids) were collected from 350 patients with uveitis or endophthalmitis. Corneal samples were also collected from 65 patients with corneal infections. Multiplex PCR was performed to screen ocular samples from the patients for HHV-1 to HHV-8. Samples were also assayed for HHV-6 DNA using quantitative real-time PCR. Primers for nested RT-PCR were designed to detect amplification of mRNA (HHV-6 A IE1 U90). PCR results indicated a total of seven patients with uveitis or endophthalmitis (7/350, 2% +) and a single patient with corneal inflammatory disease were positive for HHV-6 DNA (1/65, 1.5% +). These eight patients had high copy numbers of HHV-6 DNA, with values ranging from 4.0 × 10(3) to 5.1 × 10(6) copies/mL. Real-time PCR analysis indicated that two of these cases were HHV-6 variant A and six cases were variant B. In addition, HHV-6 mRNA was clearly detected in vitreous cells collected from one of the patients, suggesting that viral replication may occur in the eye. Our results indicate that HHV-6 infection/reactivation is implicated in ocular inflammatory diseases.

Dominance of variant A in Human Herpesvirus 6 viraemia after renal transplantation

BackgroundHuman herpesvirus 6 (HHV-6), mostly variant B reactivation in renal transplant patients has been published by other authors, but the pathogenetic role of HHV-6 variant A has not been clarified. Our aims were to examine the prevalence of HHV-6, to determine the variants, and to investigate the interaction between HHV-6 viraemia, human cytomegalovirus (HCMV) infection and clinical symptoms.MethodsVariant-specific HHV-6 nested PCR and quantitative real-time PCR were used to examine blood samples from renal transplant patients and healthy blood donors for the presence and load of HHV-6 DNA and to determine the variants. Active HHV-6 infection was proved by RT-PCR, and active HCMV infection was diagnosed by pp65 antigenaemia test.ResultsHHV-6 viraemia was significantly more frequent in renal transplant patients compared to healthy blood donors (9/200 vs. 0/200; p = 0.004), while prevalence of HHV-6 latency was not significantly different (13/200 vs. 19/200; p > 0.05). Dominance of variant A was revealed in viraemias (8/9), and the frequency of HHV-6A was significantly higher in active infections compared with latency in renal transplant patients (8/9 vs. 2/13; p = 0.0015). Latency was established predominantly by HHV-6B both in renal transplant patients and in healthy blood donors (11/13 and 18/19). There was no statistical significant difference in occurrence of HCMV and HHV-6 viraemia in renal transplant patients (7/200 vs. 9/200). Statistical analysis did not reveal interaction between HHV-6 viraemia and clinical symptoms in our study.ConclusionsContrary to previous publications HHV-6A viraemia was found to be predominant in renal transplant patients. Frequency of variant A was significantly higher in cases of active infection then in latency.

Subtype-specific, probe-based, real-time PCR for detection and typing of human herpesvirus-6 encephalitis from pediatric patients under the age of 2 years

To investigate the frequency of human herpesvirus-6 (HHV-6) encephalitis in pediatric patients under 2 years of age, we developed a method for the simultaneous detection and differentiation of the 2 variants of HHV-6 (HHV-6A and HHV-6B) using subtype-specific, probe-based, real-time PCR (SSPBRT-PCR) and which were further evaluated on 405 cerebrospinal fluid (CSF) specimens from children with suspected encephalitis. A total of 23 (5.70%) out of 405 CSF specimens were positive by SSPBRT-PCR, including 3 cases of HHV-6A and 20 cases of HHV-6B. The positive rate of HHV-6B was significantly higher than that of HHV-6A ( P = 0.0004). Compared with the results of the conventional real-time PCR, the sensitivity and specificity of the SSPBRT-PCR assay were 95.24% and 99.22%, respectively. This study suggests a role for both variants of HHV-6 in the pathogenesis of viral encephalitis. SSPBRT-PCR can provide rapid, sensitive, and specific results for identification of HHV-6A and HHV-6B and management of HHV-6 encephalitis.

Benzimidazole analogs inhibit human herpesvirus 6.

Several benzimidazole nucleoside analogs, including 1H-β-D-ribofuranosyl-2-bromo-5,6-dichlorobenzimidazole (BDCRB) and 1H-β-L-ribofuranosyl-2-isopropylamino-5,6-dichlorobenzimidazole (maribavir [MBV]), inhibit the replication of human cytomegalovirus. Neither analog inhibited the related betaherpesvirus human herpesvirus 6 (HHV-6). Additional analogs of these compounds were evaluated against both variants of HHV-6, and two L-analogs of BDCRB had good antiviral activity against HHV-6A, as well as more modest inhibition of HHV-6B replication.

Review part 2: Human herpesvirus‐6 in central nervous system diseases

AbstractJ. Med. Virol. 82:1669–1678, 2010. © 2010 Wiley‐Liss, Inc.

Translational Challenges Of Human Herpesvirus 6 Chromosomal Integration

Translational Challenges Of Human Herpesvirus 6 Chromosomal Integration

Divergent susceptibilities of human herpesvirus 6 variants to type I interferons

Two distinct human herpesvirus 6 (HHV-6) variants infect humans. HHV-6B is the etiologic agent of roseola and is associated with life-threatening neurological diseases, such as encephalitis, as well as organ transplant failure. The epidemiology and disease association for HHV-6A remain ill-defined. Specific anti-HHV-6 drugs do not exist and classic antiherpes drugs have secondary effects that are often problematic for transplant patients. Clinical trials using IFN were also performed with inconclusive results. We investigated the efficacy of type I IFN (alpha/beta) in controlling HHV-6 infection. We report that cells infected with laboratory strains and primary isolates of HHV-6B are resistant to IFN-alpha/beta antiviral actions as a result of improper IFN-stimulated gene (ISGs) expression. In contrast, HHV-6A-infected cells were responsive to IFN-alpha/beta with pronounced antiviral effects observed. Type II IFN (gamma)-signaling was unaltered in cells infected by either variant. The HHV-6B immediate-early 1 (IE1) physically interacts with STAT2 and sequestrates it to the nucleus. As a consequence, IE1B prevents the binding of ISGF3 to IFN-responsive gene promoters, resulting in ISG silencing. In comparison, HHV-6A and its associated IE1 protein displayed marginal ISG inhibitory activity relative to HHV-6B. The ISG inhibitory domain of IE1B mapped to a 41 amino acid region absent from IE1A. Transfer of this IE1B region resulted in a gain of function that conferred ISG inhibitory activity to IE1A. Our work is unique in demonstrating type I IFN signaling defects in HHV-6B-infected cells and highlights a major biological difference between HHV-6 variants.

Conservation of HHV-6 DNA polymerase processivity factor sequence and predicted structure suggests it as a target for antiviral development

The replication of human herpesvirus-6 (HHV-6) DNA is catalyzed by the viral DNA polymerase pU38 and the processivity factor pU27 which stabilizes the enzyme on the DNA template. The genetic polymorphism of pU27 among 46 clinical strains of HHV-6 variant A or B and four strains resistant to antivirals was investigated. Overall, 28 amino acid changes (7.6%) and a two-amino acid deletion were identified among the 368 residues of pU27, when using the U1102 (variant A) sequence as the reference. Eleven amino acid changes (3.0%) specifically differentiated both variants. The median intravariant amino acid variability was 1.2% and 0.3% for A and B, respectively. Except for a single change, the pU27 sequence of multi-drug resistant HHV-6 strains was also conserved. Structural models of pU27 for variants A and B were derived from that of the human cytomegalovirus homologue pUL44, and showed either identical or very similar residues in the regions interacting with viral DNA polymerase and viral DNA molecule. As pU27 is both highly conserved and essential for viral replication, it might constitute an interesting target for antiviral chemotherapy.

HHV-6 infection of tonsils and adenoids in children with hypertrophy and upper airway recurrent infections

Objective Human herpes virus 6 (HHV-6), the agent of a self-limiting exanthematic disease in childhood, persists in a silent state in the secondary lymphoid organs and the reactivation is characterized by HHV-6-induced inflammatory cytokines. This study investigates the possible etiological role of HHV-6 in children affected by tonsil and adenoid hypertrophy. Methods 55 tonsils, 80 adenoids fresh tissues and 74 blood samples were collected from 80 children (mean age 4.8 years, 43.5% female) undergoing elective tonsillectomy and/or adenoidectomy for tissue hypertrophy. Moreover, patients with <5 years old documented upper airway recurrent infections not related to relapsing of acute tonsillitis. Specific IgG antibodies and virus detection (by PCR, variant A/B enzymatic genotyping and real-time PCR) were performed. Results In our series, HHV-6 seroprevalence was tested at 50%. HHV-6 variant B was the unique strain finding in 25% of adenoids, in 12.7% of tonsils and in 4% of peripheral blood mononuclear cells (PBMCs). HHV-6-B was prevalent in tonsils of children affected by upper airway infections (17.8% vs 7.4%) while the adenoids represented the more frequent reservoir (30.7% vs 19.5%) in patients with hypertrophy. HHV-6 viral load was low, ranging from 80 to 600 copies/10 6 cells suggesting a latent/persistent phase of infection. Conclusion These results reinforce the role of the secondary lymphoid organs as an important reservoir for HHV-6B. Nevertheless, infection of lymphoid cells, sustained by a low level of replication, could be sufficient to increase the local injury through an autologous mechanism of inflammation.

Detection of human herpesvirus-6 in adult central nervous system tumors: predominance of early and late viral antigens in glial tumors

The purpose is to determine the incidence of active and latent human herpesvirus-6 (HHV-6) infection in a large cohort of adult primary and recurrent CNS tumors. We screened a tissue microarray (TMA) containing more than 200 adult primary and recurrent CNS tumors with known clinical information for the presence of HHV-6 DNA by in situ hybridization (ISH) and protein by immunohistochemistry (IHC). One hundred six of 224 (47%) CNS tumors were positive for HHV-6 U57 Major Capsid Protein (MCP) gene by ISH compared to 0/25 non tumor control brain (P = 0.001). Fourteen of 30 (47%) tumors were HHV-6 MCP positive by nested PCR compared to 0/25 non-tumor brain controls (P = 0.001), revealing HHV-6 Variant A in 6 of 14 samples. HHV-6A/B early (p41) and late (gp116/64/54) antigens were detected by IHC in 66 of 277 (24%) (P = 0.003) and 84 of 282 (35%) (P = 0.002) tumors, respectively, suggesting active infection. HHV-6 p41 (P = 0.645) and gp116/64/54 (P = 0.198) antigen detection was independent of recurrent disease. Glial tumors were 3 times more positive by IHC compared to non glial tumors for both HHV-6 gp116/64/54 (P = 0.0002) and HHV-6 p41 (P = 0.004). Kaplan Meier survival analysis showed no effect of HHV-6 gp116/64/54 (P = 0.852) or HHV-6 p41 (P = 0.817) antigen detection on survival. HHV-6 early and late antigens are detected in adult primary and recurrent CNS tumors more frequently in glial tumors. We hypothesize that the glial-tropic features of HHV-6 may play an important modifying role in tumor biology that warrants further investigation.

Detection of human herpesvirus-6 variants in pediatric brain tumors: Association of viral antigen in low grade gliomas

Background Human herpesvirus-6 (HHV-6) has been associated with a diverse spectrum of central nervous system (CNS) diseases and reported glial tropism. Objective To determine if HHV-6 is present in a series of pediatric brain tumors. Study design Pediatric gliomas from 88 untreated patients represented in a tissue microarray (TMA) were screened for HHV-6 by nested polymerase chain reaction (PCR), in situ hybridization (ISH), and immunohistochemistry (IHC) and compared to non-glial tumors ( N = 22) and control brain ( N = 32). Results were correlated with tumor grade and overall survival. Results HHV-6 U57 was detected by nested PCR in 68/120 (57%) tumors and 7/32 (22%) age-matched non-tumor brain ( P = 0.001). HHV-6 U31 was positive in 73/120 (61%) tumors and 11/32 (34%) controls ( P = 0.019). Seventy-two percent (43/60) of tumors were HHV-6 Variant A. HHV-6 U57 was confirmed by ISH in 83/150 (54%) tumors and 10/32 (31%) controls ( P = 0.021), revealing a non-lymphocytic origin of HHV-6. HHV-6A/B gp116/64/54 late antigen was detected by IHC in 50/124 (40%) tumors and 6/32 (18%) controls ( P = 0.013). Interestingly, 58% of low grade gliomas ( N = 67) were IHC positive compared to 19% of high grade gliomas ( N = 21, P = 0.002) and 25% of non-gliomas ( N = 36, P = 0.001). HHV-6A/B gp116/64/54 antigen co-localized with glial fibrillary acidic protein, confirming the astrocytic origin of antigen. Overall, there was no primary association between HHV-6A/B gp116/64/54 antigen detection and survival ( P = 0.861). Conclusions We provide the first reported series of HHV-6 detection in pediatric brain tumors. The predominance of HHV-6 in glial tumors warrants further investigation into potential neurooncologic disease mechanisms.

Prevalence of HHV‐6 integrated chromosomally among children treated for acute lymphoblastic or myeloid leukemia in the Czech Republic

Chromosomal integration of human herpesvirus 6 (HHV-6) is a novel situation found in a small percentage of individuals. While active HHV-6 infection is treatable using antivirals, the abnormally high level of HHV-6 DNA found in chromosomal integration of HHV-6 (CI-HHV-6) is not affected by such drugs. Stored DNA samples taken originally for detection of fusion genes and minimal residual disease from 339 pediatric patients treated for leukemia in the Czech Republic between the years 1995-2007 were tested retrospectively. Using real-time quantitative PCR technology, the quantity of HHV-6 DNA detected was normalized to 100,000 human genome equivalents as assessed by quantitation of the albumin gene. HHV-6 DNA was detected in 107 samples from 91 patients (26.8%). In the majority of samples (99) only a minute level of normalized viral copies (NVCs) (median 1.84 NVCs) was detected. A high viral load of approximately 100,000 NVCs was detected in 5 patients (1.5%; median 140,150 NVCs), in all of whom were confirmed subsequently CI-HHV-6 by a detection of HHV-6 DNA in hair follicles or in the nails. In all but one patient with HHV-6 variant B, variant A of the virus was detected. None of the patients with CI-HHV-6 had complications attributable to HHV-6 infection. The prevalence of CI-HHV-6 in childhood leukemia does not differ from that published for other patients or healthy populations. Where high levels of HHV-6 DNA are present, CI-HHV-6 should be confirmed as soon as possible so that potentially toxic but ineffective antiviral treatment can be stopped.

Human Herpesvirus 6 Rhombencephalitis in Immunocompetent Children

This article describes the clinical presentation, diagnostic workup, and neurologic outcome of 3 immunocompetent pediatric patients diagnosed with human herpesvirus 6 (HHV6) rhombencephalitis. Presentation of HHV6 rhombencephalitis included new onset seizures, ataxia, encephalopathy, and opsoclonus-myoclonus. Neurologic examination revealed cranial neuropathies, cerebellar dysfunction, and extremity weakness. Magnetic resonance imaging abnormalities located in the cerebellum, basal ganglia/thalamus, and cerebral hemispheres were detected in 2 patients. Diagnosis of HHV6 encephalitis was made by real-time and nested polymerase chain reaction of serum and cerebrospinal fluid. The HHV6 variant A was detected in 2 patients by sequence analysis, and HHV6 protein was detected by immunomicroscopy in a patient who underwent biopsy secondary to progressive clinical and neuroradiographic findings. Therapy with intravenous ganciclovir did not correlate with resolution of neurologic symptoms, despite eventual non-detectable HHV6. Human herpesvirus 6 should be considered in the differential diagnosis of unexplained cases of rhombencephalitis in immunocompetent children. Features may be rapidly progressive and include profound encephalopathy, seizures, ataxia, and opsoclonus-myoclonus.

Downregulation of the T-Cell Receptor Complex and Impairment of T-Cell Activation by Human Herpesvirus 6 U24 Protein

We have performed a screen aimed at identifying human herpesvirus 6 (HHV-6)-encoded proteins that modulate immune recognition. Here we show that the U24 protein encoded by HHV-6 variant A downregulates cell surface expression of the T-cell receptor (TCR)/CD3 complex, a complex essential to T-cell activation and the generation of an immune adaptive response. In the presence of U24, the TCR/CD3 complex is endocytosed but is not recycled back to the plasma membrane. Instead, it accumulates in early and late endosomes. Interestingly, whereas CD3 downregulation from the cell surface is normally associated with T-cell activation, U24 downregulates CD3 independently of T-cell activation. Moreover, we found that U24-expressing T cells are resistant to activation by antigen-presenting cells. HHV-6 has evolved a unique mechanism of inhibition of T-cell activation that may impair the establishment of an adaptive immune response. Furthermore, lymphocyte activation creates an environment favorable to the reactivation and replication of lymphotropic herpesviruses. Thus, by inhibiting T-cell activation, HHV-6 might limit its reactivation and thus minimize immune recognition.

Human Herpesvirus 6 (HHV-6) Induces Dysregulation of Glutamate Uptake and Transporter Expression in Astrocytes

Human herpesvirus 6 (HHV-6) infects and establishes latency in the central nervous system (CNS). Reactivation of latent HHV-6 has been associated with neurologic diseases including epilepsy and multiple sclerosis (MS). In vivo, HHV-6 has been localized to astrocytes and can infect human astrocytes in vitro, suggesting that this virus may have a tropism for glial cells and may affect glial cell function. An essential role of astrocytes in the CNS is active maintenance of the excitatory neurotransmitter glutamate. Dysregulation of glutamate has been implicated as a potential mechanism of disease in both epilepsy and MS. Both disorders have demonstrated elevated glutamate in CSF and may be associated with dysregulation of glutamate signaling, uptake, and metabolism. This study demonstrates dysregulation of glutamate uptake in human astrocytes infected with both variants of HHV-6, A and B, with differential effects of HHV-6 in acute and persistently infected cells. Whereas astrocytes acutely infected with HHV-6 demonstrated increased glutamate uptake, cells persistently infected with HHV-6A and HHV-6B demonstrated impaired glutamate uptake. Functional dysregulation of glutamate uptake was associated with early increases in mRNA and protein expression of the glial glutamate transporter EAAT-2 followed by a sustained decrease in mRNA expression in astrocytes infected with both HHV-6A and HHV-6B. Dysregulated glutamate uptake and transporter expression suggests a mechanism for dysregulation of glutamate levels in vivo and a potential mechanism for virus-associated neurologic disease.