Brief report: fatal encephalitis due to variant B human herpesvirus-6 infection in a bone marrow-transplant recipient

Human herpesvirus 6 and multiple sclerosis: systemic active infections in patients with early disease

By means of immunohistochemical staining, cells actively infected with human herpesvirus 6 (HHV-6) were found in central nervous system tissues from 8 (73%) of 11 patients with definite multiple sclerosis (MS). Interestingly, 17 (90%) of 19 tissue sections showing active demyelination were positive for HHV-6-infected cells compared with only 3 (13%) of 23 tissue sections free of active disease (P<.0001). Central nervous system tissues from 2 of 28 normal persons and patients with other inflammatory demyelinative diseases were positive for HHV-6-infected cells (P<.0001), and the 2 positive cases were diagnosed as having HHV-6 leukoencephalitis. By use of a rapid culture assay, blood samples from 22 (54%) of 41 patients with definite MS were found to contain active HHV-6 infections, compared with 0 of 61 normal controls (P<.0001). No significant difference was found between HHV-6 viremia-positive and HHV-6 viremia-negative MS patients with respect to type of disease (relapsing/remitting or progressive). In contrast, patients with active HHV-6 viremia were significantly younger and had shorter durations of disease than did HHV-6 viremia-negative patients.

Reactivation of human herpesviruses after allogeneic peripheral blood stem cell transplantation and bone marrow transplantation

Reactivation of latent herpesviruses results in outcomes ranging from asymptomatic shedding of viruses to severe diseases, depending on the immunological competence of the host. Severe and prolonged suppression of cellular and humoral immunity after hematopoietic stem cell transplantation is accompanied by a high incidence of symptomatic recurrent herpesvirus infections. Subclinical reactivation also occurs more frequently than previously expected in transplant recipients. An increasing viral load in the blood detected by an antigenemia assay or PCR and viral shedding in regional fluids have a predictive value for subsequent diseases. Monitoring of viral DNA in the peripheral blood after allogeneic bone marrow transplantation (allo-BMT) reveals unique temporal profiles of detection for each herpesvirus. Recent studies demonstrate that recovery of CD4+ T cells is enhanced within one month after allogeneic peripheral blood stem cell transplantation (allo-PBSCT) compared to allo-BMT. To clarify whether this immunological advantage could affect the reactivation of human herpesvirus (HHV), we monitored the emergence of viral DNA by a nested-double polymerase chain reaction in peripheral blood leukocytes. Detection rates of HHV-6 DNAs which peak at 3-4 weeks post-transplant, were significantly reduced after allo-PBSCT compared to allo-BMT, while those of other herpesviruses which tend to be reactivated later than this period (Epstein-Barr virus and cytomegalovirus) were similar between the two types of transplants. Detection of HHV-6 DNA within the first month after the transplant was associated with delayed platelet engraftment. These results underscore the important role of CD4+ T reconstitution in inhibiting virus reactivation post-transplant.

Human herpesvirus 6 is an important pathogen in infectious lung disease after allogeneic bone marrow transplantation

Two hundred and ten bronchoalveolar lavage (BAL) samples were obtained from 50 patients 10 days before and on defined days after allogeneic bone marrow transplantation (BMT). The samples were examined for human cytomegalovirus (HCMV) and human herpesvirus-6 (HHV-6) by polymerase chain reaction (PCR). Fifteen patients (30%) had a positive result for HCMV in at least one sample and 25 (50%) were positive for HHV-6 in at least one sample. Five patients developed HCMV-associated interstitial pneumonia (HCMV-IP) within 100 days after allogeneic BMT. Four of these patients were positive for both HCMV and HHV-6. Conspicuous HHV-6 positivity was detected in BAL samples obtained because of respiratory symptoms. No association was found between detection of HHV-6 and acute graft-versus-host disease. Engraftment failure or a delay in engraftment was observed in none of the 50 patients. The data from this study indicate that HHV-6 is a pathogen in HCMV-associated, as well as in non-HCMV-associated infectious lung disease after BMT.

Infections of the central nervous system in transplant recipients

Central nervous system (CNS) infections, accounting for 4-29% of CNS lesions in transplant recipients, are a significant post-transplant complication. Focal CNS infectious lesions or brain abscesses have been documented in 0.36-1% of the transplant recipients. Mycelial fungi, particularly Aspergillus, are by far the most frequent etiologies of post-transplant brain abscesses. Bacteria, with the exception of Nocardia, are rarely associated with brain abscesses in transplant recipients. Time of onset and concurrent extraneural lesions have implications relevant towards invasive diagnostic procedures in transplant recipients with brain abscesses. Meningoencephalitis in transplant recipients is predominantly due to viruses, e.g., herpesviruses, and less frequently due to Listeria monocytogenes, Toxoplasma gondii, and Cryptococcus. Despite a wide, and at times perplexing array of opportunistic pathogens that can cause CNS infections, the temporal association of the infection with the time elapsed since transplantation, risk factors, clinical manifestations, and neuroimaging characteristics of the lesion can allow a reasoned and rational approach towards the recognition, diagnosis, and appropriate management of CNS infections in transplant recipients.

Infantile convulsions with mild gastroenteritis

The development of sensitive new molecular genetic techniques has led to the detection of rotavirus in cerebrospinal fluid, stools and throat swabs from patients with gastroenteritis with accompanying clinical symptoms similar to infantile benign convulsions. Small round structured virus (SRSV) has also been found in stools of patients with similar clinical symptoms by a new procedure. However, the mechanism by which these viral infections induce benign convulsions remains to be elucidated. The present paper reviews recent virological and clinical studies of seizures probably caused by gastroenteritis viruses including rotavirus, SRSV and other viruses.

Encephalitis caused by human herpesvirus-6 in transplant recipients: relevance of a novel neurotropic virus

BACKGROUND

Human herpesvirus-6 (HHV-6) is a neurotropic virus. Encephalitis is a significant clinical manifestation of HHV-6; however, sparse data on this entity exist in transplant recipients.

METHODS

Cases of HHV-6 encephalitis reported in the literature (13 bone marrow transplant recipients and 1 liver transplant recipient) were reviewed. The diagnosis was established in all by viral isolation and/or detection of HHV-6 DNA in the cerebrospinal fluid by polymerase chain reaction or histopathologic method.

RESULTS

HHV-6 encephalitis occurred a median of 45 days (range 10 days to 15 months) after transplantation. Mental status changes, ranging from confusion to coma (92%), seizures (25%), and headache (25%) were the predominant clinical presentations. Focal neurologic findings occurred in only 17% of the patients. Twenty-five percent of the patients had fever; however, the height of fever (< or =40 degrees C) in febrile patients was striking. Cerebrospinal fluid pleocytosis was generally lacking. Abnormal neuroimaging findings, characterized by low-attenuation lesions in the posterior cerebral lobes, were present only in 17% of the patients. Overall mortality in patients with HHV-6 encephalitis was 58% (7 of 12); 42% (5 of 12) of the deaths were caused by HHV-6. Cure was documented in 7 of 8 patients who received ganciclovir or foscarnet for > or =7 days, compared with 0% (0 of 4) in those who did not receive these drugs or received them for < 7 days (P=.01).

CONCLUSIONS

HHV-6 may be associated with encephalitis after transplantation and warrants consideration in transplant recipients with encephalitis of unidentifiable etiology.

Human herpesvirus-6 antigenemia after liver transplantation

BACKGROUND

Human herpesvirus (HHV)-6 has recently been reported in liver transplant patients. It infects and causes dysfunction in hepatic transplants, which provides serious differential diagnostic problems between allograft rejection and viral infection. The diagnosis of posttransplantation HHV-6 infection is usually based on serology or on polymerase chain reaction detection of viral DNA in peripheral blood specimens. However, serology does not tell the exact time of the infection, and detection of viral DNA by polymerase chain reaction may also indicate a latent infection in seropositive patients. Here we report the diagnostic use of frequent monitoring of HHV-6 antigenemia after liver transplantation.

METHODS

Altogether 622 blood specimens from 51 consecutive adult liver transplant patients were analyzed. The diagnosis was based on demonstration of HHV-6-specific antigens in peripheral blood mononuclear cells using immunoperoxidase staining and monoclonal antibodies and on serology.

RESULTS

During the first year (7-280 days) after transplantation, HHV-6 infection was diagnosed in 11 (22%) of 51 patients. HHV-6 early antigens, as well as HHV-6 variant B antigens, were detected in all 11 patients. HHV-6 diagnosis was confirmed by serology. The episode of HHV-6 antigenemia usually lasted for several weeks together with mild, if any, clinical signs of the infection. A significant graft dysfunction was associated with HHV-6 antigenemia in 8 of 11 patients, and viral antigens were also detected in the liver biopsy specimens of 3 of these patients.

CONCLUSIONS

An active HHV-6 infection can be diagnosed from peripheral blood by detection of virus-specific antigens in mononuclear cells. HHV-6 antigenemia correlated with seroresponse.

Human herpesvirus-6 and -7 infections in children: agents of roseola and other syndromes

Human herpesvirus-6 (HHV-6) and -7 (HHV-7) infections typically are silent or manifested as mild febrile illnesses including classic roseola. In addition, case reports and epidemiologic data support the rare occurrence of HHV-6 encephalitis in immunocompromised as well as immunocompetent subjects. Although many other diseases have been putatively associated with HHV-6 or HHV-7, these associations are not well documented due to small numbers, use of tests incapable of distinguishing latent from replicating virus, potential virus cross-reactivity, or contradictory results. Further careful studies are needed to confirm these disease associations. Laboratory tests for diagnosing active HHV-6 and HHV-7 infections include virus culture, antigen detection, and polymerase chain reaction of cell-free biologic fluid. Although HHV-6 and HHV-7 are inhibited by several antiviral drugs in the laboratory, including ganciclovir and foscarnet, no clinical trials have assessed their benefit. Nevertheless, treatment may be considered for patients with serious HHV-6- or HHV-7-associated disease confirmed with accurate virologic tests.

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.

HLA-mismatched CD34-selected stem cell transplant complicated by HHV-6 reactivation in the central nervous system

We report here a patient who suffered from PCR- confirmed human herpesvirus type 6 (HHV-6) meningoencephalitis after allogeneic purified CD34+ cell transplantation from his HLA-mismatched sibling donor, even though he had been on intense prophylaxis with i.v. ganciclovir (GCV), acyclovir (ACV) and gamma-globulin containing a specific antibody against HHV-6. Serological evaluation disclosed that both the donor and recipient had IgG antibody against HHV-6 before transplantation. His blood WBC count started to transiently increase on day 10, and all blood components had decreased by day 20. He then developed a severe headache and high blood pressure, and sporadic abnormal neurological findings including nystagmus and delirium. An analysis of cerebrospinal fluid (CSF) revealed 8 cells/microl, a glucose level of 130 mg/dl and a protein level of 201 mg/dl (normal, 50 mg/dl) on day 26. At the time, HHV-6 was detected only in CSF by a PCR-based method and he was diagnosed as having meningoencephalitis due to the local reactivation of HHV-6. Although he failed to respond to high-dose therapy with ACV (60 mg/kg/day) and gamma-globulin, the DNA of this virus disappeared from the CNS upon treatment with GCV (30 mg/kg/day) combined with the intraventricular infusion of alpha-interferon. His clinical course was further complicated with meningoencephalitis due to staphylococcus epidermidis, and he died of tentorial herniation on day 79 without the recovery of blood components. This experience may indicate that intense prophylaxis to prevent reactivation of HHV-6 in the CNS is essential for the management of such profoundly immunosuppressed patients.

Reactivation of human herpesvirus 6 by infection of human herpesvirus 7

We have attempted to reactivate human herpesvirus 6 (HHV-6) by infection with HHV-7 using childhood exanthem subitum patients in vitro. Peripheral blood mononuclear cells (PBMCs) were collected from children who had a history of exanthem subitum(ES) by HHV-6 and were infected by human herpesvirus 7 (HHV-7) in vitro. The antigen positive rate to HHV-6 started to increase 7 days after the infection and reached a maximum by Day 15 using an immunofluorescence antibody test. The copy number of HHV-6 DNA also increased in the samples in 10 days after infection in vitro. No antigen or increase in DNA was detected in PBMCs, that were mock-infected or infected with supernatant of stock virus after ultracentrifugation, suggesting that an infection by HHV-7 is necessary to reactivate HHV-6. In the paired sera samples during the acute and the convalescent phases of ES, seven to ten bands, that were specific for HHV-6, were recognized in samples from the acute phase, and at least 5 dominant polypeptides were found more intensively after HHV-7 infection.

In situ hybridization detection of human herpesvirus 6 in brain tissue from fatal encephalitis

A 23-month-old girl died after 2 days' illness with rash, fever, and convulsions. Neuropathologic findings were consistent with viral hemorrhagic encephalitis in pontine tegmentum and medial thalamic areas. Human herpesvirus 6 (HHV-6) DNA was detected in pontine nuclei by in situ hybridization. In addition, polymerase chain reaction for HHV-6 of serum and paraffin-embedded pontine tissue was positive, and serology indicated an acute primary infection. This is the first case showing HHV-6 DNA in the brain cells of an immunocompetent patient with acute encephalitis.

CD46 is a cellular receptor for human herpesvirus 6

Human herpesvirus 6 (HHV-6) is the etiologic agent of exanthema subitum, causes opportunistic infections in immunocompromised patients, and has been implicated in multiple sclerosis and in the progression of AIDS. Here, we show that the two major HHV-6 subgroups (A and B) use human CD46 as a cellular receptor. Downregulation of surface CD46 was documented during the course of HHV-6 infection. Both acute infection and cell fusion mediated by HHV-6 were specifically inhibited by a monoclonal antibody to CD46; fusion was also blocked by soluble CD46. Nonhuman cells that were resistant to HHV-6 fusion and entry became susceptible upon expression of recombinant human CD46. The use of a ubiquitous immunoregulatory receptor opens novel perspectives for understanding the tropism and pathogenicity of HHV-6.

Presence of human herpesviruses 6, 7, and 8 DNA sequences in normal brain tissue

The three novel human herpesviruses (HHV) 6, 7, and 8 are predominantly, but not exclusively, lymphotropic. In an attempt to elucidate their neurotropism in vivo, viral DNA sequences present in fresh autopsy cortical brain tissues obtained from 84 consecutive Chinese subjects (mean age, 66.9 years; range, 21-98 years) were detected by a nested polymerase chain reaction. These patients were apparently immunocompetent and free of clinical signs of viral diseases. HHV-6 DNA was detected in 36 of 84 (42.9%) patients, and the DNA-positive and -negative groups did not show a significant difference in age or sex distribution. Of the 36 HHV-6 DNA-positive cases, 9 (25%) were variant A and 27 (75%) were variant B. In view of the lower prevalence of variant A than variant B in the adult population, the two variants may share a comparable neuroinvasive potential. HHV-7 and HHV-8 DNA were detected respectively in three and two patients. The low positive rates of HHV-7 and HHV-8 may represent a relatively lower neuroinvasive potential of the viruses. Alternatively, the localization of HHV-7 and HHV-8 may be more restricted and the sampled cortical tissues may not represent the most abundant site of persistence in the nervous system. The results provide molecular evidence of the presence of the three newly identified herpesviruses in brain tissue. The pathogenic role for HHV-7 and HHV-8, as with HHV-6, in neurological diseases should not be overlooked.

Human herpesviruses 6 and 7 as potential pathogens after liver transplant: prospective comparison with the effect of cytomegalovirus

Because cytomegalovirus (CMV) is an important opportunistic infection after liver transplant, we conducted a prospective study to see if the same applied to human herpesviruses (HHV)-6 and -7. We used polymerase chain reaction (PCR) methods optimised to detect active, not latent, infection and studied patients not receiving antiviral prophylaxis for CMV. Post-transplant, 536 blood samples were tested by PCR (median 7; range 4-50). Active infection with CMV was detected in 28/60 (47%), HHV-6 in 19/60 (32%), and HHV-7 in 29/60 (48%) of patients. The PCR-positive samples were tested by quantitative-competitive PCR to measure the virus load of each betaherpesvirus. The median peak virus load for CMV was significantly greater than that for HHV-6 or HHV-7. Detailed clinicopathological analyses for the whole population showed that CMV and HHV-6 were each significantly associated with biopsy-proven graft rejection. Individual case histories suggested that HHV-6 and HHV-7 may be the cause of some episodes of hepatitis and pyrexia. It is concluded that HHV-6 is a previously unrecognized contributor to the morbidity of liver transplantation, that HHV-7 may also be important and that both viruses should be included in the differential diagnosis of graft dysfunction.

Novel, nonconsensus cellular splicing regulates expression of a gene encoding a chemokine-like protein that shows high variation and is specific for human herpesvirus 6

There are few genes that are specific and diagnostic for human herpesvirus-6. U83 and U22 are two of them. U22 is unique, whereas U83 encodes distant similarity with some cellular chemokines. Reverse transcription-polymerase chain reaction, cDNA cloning, and sequence analyses show polyadenylated RNA transcripts corresponding to minor full-length and abundant spliced forms of U83 in human herpesvirus 6-infected cells. The splice donor and acceptor sites do not fit consensus sequences for either major GT-AG or minor AT-AC introns. However, the spliced form can also be detected in a U83 transfected cell line; thus the novel sites are used by cellular mechanisms. This intron may represent a new minor CT-AC splicing class. The novel splicing regulates gene expression by introducing a central stop codon that abrogates production of the chemokine-like molecule, resulting in an encoded truncated peptide. The use of metabolic inhibitors and an infection time course showed expression of the two RNA transcripts with immediate early kinetics. However, the full-length product accumulated later, dependent on virus DNA replication, similar to U22. Sequence analyses of 16 strains showed high variation (13%) in U83, with conservation of the novel splice sites. Representative strain variants had similar kinetics of expression and spliced products.

Human herpes virus 6 fatal encephalitis in a bone marrow recipient

Human herpes virus 6 (HHV-6) has been implicated as a human pathogen in both normal and immunocompromised hosts. It has been associated with interstitial pneumonitis and bone marrow suppression after transplantation. We report here a case of fatal encephalitis in a bone marrow transplant recipient. This case illustrates the importance of considering HHV6 as an emerging pathogen in immunocompromised hosts.

Encephalopathy associated with human herpesvirus 6 in a liver transplant recipient

Recent reports have documented human herpesvirus 6 (HHV-6) as a cause of high fever, bone marrow depression, and rash in liver transplant recipients in the absence of another known pathogen. We describe a 49-year-old liver transplant recipient who developed confusion, occipital headache, and involuntary movements of the limbs 3 weeks after orthotopic liver transplantation. HHV-6 was detected in the peripheral blood using a rapid culture assay. Examination of cerebrospinal fluid by polymerase chain reaction for HHV-6 was also positive. No other pathogens were identified. The patient improved after commencement of intravenous ganciclovir therapy. This case suggests HHV-6 needs to be considered in the differential diagnosis of unexplained confusion in liver transplant recipients.

Human herpesvirus-6 infection in children with cancer

Pediatric cancer patients treated with multimodal therapy are at a great risk of opportunistic infections or reactivation of latent infections. Human herpesvirus-6 (HHV-6) can serve as an example of such infection, with high seroprevalence in population. In 66 children with cancer and in 45 healthy controls, age matched, the presence of DNA HHV-6 was examined in peripheral blood by the polymerase chain reaction method. HHV-6 serology was also performed. No difference has been found between patients at the time of cancer diagnosis and the group of healthy children in the presence of DNA HHV-6 in blood, 17.4 and 15.6%, respectively. During cytotoxic chemotherapy the presence of HHV-6 in peripheral blood raised to 37.1% in patients with fever. Other parameters and symptoms such as febrile neutropenia, lymphopenia, exanthem, hepatopathy, lymphadenopathy, enteritis, bone marrow aplasia, pneumonitis, and encephalitis were examined in both the HHV-6 positive and HHV-6 negative groups of pediatric cancer patients. Statistically significant differences (p < .05) were found in case of lymphopenia, exanthem, and hepatopathy. In 4 out of 66 patients (6.1%) severe HHV-6 infection has been found: in 3 patients during cytotoxic chemotherapy and in 1 at the time of cancer diagnosis. Reactivation of HHV-6 infection in pediatric cancer patients under treatment with cytotoxic chemotherapy is frequent and can lead to severe complications as described in patients after bone marrow or organ transplantation.

Detection of human herpesviruses 6 and 7 genomic sequences in brain tumours

BACKGROUND

Human herpesviruses 6 and 7 (HHV-6, HHV-7) are ubiquitous, with primary infection occurring early in life followed by persistence, which may involve neural tissue. While HHV-6 and HHV-7 are predominantly T lymphotropic, the extent of tissue tropism in persistent infection is not known.

AIM

To investigate neuropersistence and the role of HHV-6 and HHV-7 in brain tumorigenesis.

METHODS

Nested polymerase chain reaction was used to detect HHV-6 and HHV-7 genomic sequences in preparations of total DNA extracted from 98 formalin fixed, paraffin embedded primary brain tumours. HHV-6 detected was further characterized into variants A and B by restriction fragment length analysis.

RESULTS

HHV-6 was detected in 8.2% of cases and HHV-7 in 14.3% (14/98). None of the positive samples contained both viruses. Among the eight HHV-6 positive tumours, three harboured variant A and five variant B. Four of the five ependymomas studied contained viral DNA. Otherwise, both HHV-6 and HHV-7 were present at similar low frequencies in most of the tumour types investigated.

CONCLUSIONS

The findings do not support an aetiological role of HHV-6 and HHV-7 in primary brain tumour, but they suggest that HHV-6 and HHV-7 are neurotropic in vivo and that the central nervous system seems to be one of the reservoirs for persistent infection.

Temporally-specific retrograde amnesia in two cases of discrete bilateral hippocampal pathology

The role of the hippocampus in retrograde amnesia remains controversial and poorly understood. Two cases are reported of discrete bilateral hippocampal damage, one of which was a rare case of limbic encephalitis secondary to the human herpes virus 6. Detailed memory testing showed marked anterograde memory impairment, but only mild, temporally-limited retrograde amnesia that covered a period of several years in both autobiographical and factual knowledge domains. The absence of extensive retrograde amnesia in these two cases points to a time-limited role for the hippocampus in the retrieval of retrograde memories, and suggests that entorhinal, perirhinal, parahippocampal, or neocortical areas of the temporal lobe may be more critical than the hippocampus proper for long-term retrograde memory functioning. Our findings offer general support to theories of memory consolidation that propose a gradual transfer of memory from hippocampal to neocortical dependency.

Human herpesvirus 6 open reading frame U83 encodes a functional chemokine

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

Concepts of viral pathogenesis of multiple sclerosis

Viral infections have long been suspected to cause or modulate the pathogenesis of multiple sclerosis. Recently, two viruses in particular have been associated with multiple sclerosis: human herpesvirus-6 and a retrovirus termed multiple sclerosis-associated retrovirus, which is a member of the human endogenous retrovirus-9 family. Reports on the detection of human herpesvirus-6-encoded proteins in and around multiple sclerosis lesions are intriguing. Serological and polymerase chain reaction analyses looking for signs of reactivation of human herpesvirus-6 in multiple sclerosis patients are ambiguous, however. If human herpesvirus-6 does play a role as an initiator or amplifier of inflammatory lesions in some multiple sclerosis patients, these individuals might benefit from antiviral therapy.

CT and MRI manifestations of central nervous system infection following allogeneic bone marrow transplantation

AIM

To determine the frequency, microbiological diversity and radiological patterns of central nervous system (CNS) infection following allogeneic bone marrow transplantation (BMT).

PATIENTS AND METHODS

Two neuroradiologists retrospectively reviewed the computed tomography (CT) and magnetic resonance imaging (MRI) examinations of a large cohort of bone marrow recipients. The radiological findings were correlated with clinical, microbiological and pathological data.

RESULTS

During an 8-year period 406 patients underwent allogeneic BMT; a total of 11 infections of the CNS were diagnosed in nine patients [sino-orbital aspergillosis (3), cerebral aspergillosis (2), pseudomonas (1), listeria (1), human herpes virus-6 (1), herpes zoster (1), toxoplasmosis (1) and progressive multifocal leucoencephalopathy (1)]. The radiological abnormalities could be divided into one or more of the following pathological entities: (i) focal lesions, (ii) invasive sinusitis, (iii) cerebral infarction, (iv) demyelination, (v) encephalitis and (vi) meningitis/hydrocephalus.

CONCLUSIONS

Approximately 2% of bone marrow recipients developed an infection of the CNS. The spectrum of infection changed over time and was related to predictable deficits in host immunity. The radiological appearances were diverse and corresponded to several different pathological processes.

Human herpesvirus 6 infects dendritic cells and suppresses human immunodeficiency virus type 1 replication in coinfected cultures

Human herpesvirus 6 (HHV-6) has been implicated as a cofactor in the progressive loss of CD4(+) T cells observed in AIDS patients. Because dendritic cells (DC) play an important role in the immunopathogenesis of human immunodeficiency virus (HIV) disease, we studied the infection of DC by HHV-6 and coinfection of DC by HHV-6 and HIV. Purified immature DC (derived from adherent peripheral blood mononuclear cells in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4) could be infected with HHV-6, as determined by PCR analyses, intracellular monoclonal antibody staining, and presence of virus in culture supernatants. However, HHV-6-infected DC demonstrated neither cytopathic changes nor functional defects. Interestingly, HHV-6 markedly suppressed HIV replication and syncytium formation in coinfected DC cultures. This HHV-6-mediated anti-HIV effect was DC specific, occurred when HHV-6 was added either before or after HIV, and was not due to decreased surface expression or function of CD4, CXCR4, or CCR5. Conversely, HIV had no demonstrable effect on HHV-6 replication. These findings suggest that HHV-6 may protect DC from HIV-induced cytopathicity in AIDS patients. We also demonstrate that interactions between HIV and herpesviruses are complex and that the observable outcome of dual infection is dependent on the target cell type.

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 latently infects mononuclear cells but not liver tissue

AIM

To investigate whether human herpesvirus 6 (HHV-6) can cause latent infection of liver tissue.

METHODS

Peripheral blood and liver tissue were collected from 25 living related liver transplant recipients at the time of transplantation. An avidin-biotin complex peroxidase method was used to identify HHV-6 antigen in the liver tissue. A nested polymerase chain reaction (PCR) was used to detect HHV-6 DNA in the liver tissue and mononuclear cells. Variant of HHV-6 was determined by the presence of the Hind III site in a second PCR product.

RESULTS

Immunohistochemical analysis for HHV-6 antigen was negative in all the liver specimens. HHV-6 DNA was not detected in liver tissue. Virus DNA was detected in peripheral blood mononuclear cells in nine of 25 recipients. All nine HHV-6 identified in the mononuclear cells were variant B.

CONCLUSIONS

HHV-6 variant B latently infects mononuclear cells but not liver tissue.

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.

Organ recovery from a donor with presumed viral encephalitis: a case report and review

This article reviews the pathophysiology of viral encephalitis, which is specifically infectious to transplant recipients, and discusses the potential infectivity of donors who had this virus. In addition, the case report demonstrates one center's experience in placing organs from a donor who was presumed--but not confirmed--to have viral encephalitis. When a patient with viral encephalitis is considered for organ donation, it is recommended that a brain biopsy be obtained prior to organ placement to identify the suspected virus or confirm the absence of any viral entity.

U94 of human herpesvirus 6 is expressed in latently infected peripheral blood mononuclear cells and blocks viral gene expression in transformed lymphocytes in culture

Human herpesvirus 6 (HHV-6) like other herpesviruses, expresses sequentially immediate early (IE), early, and late genes during lytic infection. Evidence of ability to establish latent infection has not been available, but by analogy with other herpesviruses it could be expected that IE genes that regulate and transactivate late genes would not be expressed. We report that peripheral blood mononuclear cells of healthy individuals infected with HHV-6 express the U94 gene, transcribed under IE conditions. Transcription of other IE genes (U16/17, U39, U42, U81, U89/90, U91) was not detected. To verify that U94 may play a role in the maintenance of the latent state, we derived lymphoid cell lines that stably expressed U94. HHV-6 was able to infect these cells, but viral replication was restricted. No cytopathic effect developed. Furthermore, viral transcripts were present in the first days postinfection and declined thereafter. A similar decline in the level of intracellular viral DNA also was observed. These findings are consistent with the hypothesis that the U94 gene product of HHV-6 regulates viral gene expression and enables the establishment and/or maintenance of latent infection in lymphoid cells.

A practitioner's guide to human herpesvirus-6 (HHV-6) and human herpesvirus-7 (HHV-7)

Human herpesvirus-6 (HHV-6) and HHV-7 are newly recognized ubiquitous human viruses first discovered in patients with AIDS or lymphoproliferative disorders. Much more information is available about the clinical characteristics of infection with HHV-6 than HHV-7. Primary infection with HHV-6 occurs in early childhood and is most commonly manifested as an undifferentiated highly febrile illness, with seizures noted to be the most common complication. A subset of children develop the classic manifestations of roseola infantum or exanthem subitum. Other neurologic diseases in adults such as encephalitis and multiple sclerosis also have been linked to HHV-6; however, the role of HHV-6 in these clinical entities has not been fully elucidated. Although HHV-6 and HIV are both tropic for CD4+ lymphocytes and interact in vitro, there is no evidence at present that HHV-6 plays a role in HIV disease. HHV-7 is similar to HHV-6 in genetic organization and structure. Little is known of the clinical characteristics of infection with HHV-7 or its ability to cause disease in children or reactivation in adults.

Meningoencephalitis caused by human herpesvirus-6 in an immunocompetent adult patient: case report and review of the literature

Human herpesvirus-6 (HHV-6) is the etiologic agent of roseola infantum, and has been implicated as a possible cause of encephalitis in pediatric and adult patients. A case of meningoencephalitis in an otherwise healthy, immunocompetent 59-year-old woman is described. The diagnosis of HHV-6 meningoencephalitis was confirmed by detecting viral DNA in cerebrospinal fluid collected in the acute stage of the disease by polymerase chain reaction. The patient was treated with acyclovir and recovered without any sequelae. The current knowledge of the pathophysiology, clinical course and outcome of HHV-6 meningoencephalitis in immunocompetent adult patients is also reviewed.

Cytomegalovirus and human herpesvirus 6 both cause viral disease after renal transplantation

BACKGROUND

Systemic viral disease after renal transplantation, especially after treatment with OKT3 or antithymocyte globulin, has usually been attributed to cytomegalovirus (CMV) infection. Identification of human herpesvirus 6 (HHV6) has raised the possibility that infection or reactivation of this virus may also occur in the same setting.

METHODS

We thus examined the incidence of CMV and HHV6 infection in a prospective blinded consecutive series of 30 renal and renal/pancreas transplant patients, 22 of whom received OKT3, antithymocyte globulin, or both.

RESULTS

Clinical diagnosis of a viral syndrome was made in 15 patients. Three patients with only HHV6 DNA in urine or serum had fever and abnormal liver function but not neutropenia. All five CMV-seronegative patients who received positive kidneys developed moderate to severe disease with fever and neutropenia but also had HHV6 DNA in urine or serum. Seven CMV-seropositive patients developed disease, mostly after OKT3/antithymocyte globulin, but six shed both CMV and HHV6 in urine or serum. The simultaneous detection of both HHV6 and CMV DNA in either urine or serum was the strongest predictor of disease (and also the severity of disease), with an odds ratio of 99.0 (95% confidence intervals 5.4-1814, P<0.002).

CONCLUSION

Most systemic viral disease after renal transplantation may be due to either coinfection or reactivation of CMV and HHV6 together. A wider understanding of risk factors for severe viral disease in this setting may come from testing for both viruses in all donors and patients in both clinical practice and clinical trials.

Human herpesvirus 6 infection and associated pathogenesis following bone marrow transplantation

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

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

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