Plaque-associated expression of human herpesvirus 6 in multiple sclerosis

Definition of a divergent epitope that allows differential detection of early protein p41 from human herpesvirus 6 variants A and B

The human herpesvirus 6 (HHV-6) early protein, p41, encoded by the U27 gene has been detected in oligodendrocytes of multiple sclerosis (MS) patients by using a monoclonal antibody (MAb to p41/38). We here report the antigenic epitope of HHV-6 p41 recognized by this MAb. First, we established that the MAb to p41/38 recognizes a nuclear antigen in HHV-6A strain GS-infected cells but not in HHV-6B strain Z29-infected cells. Secondly, we compared the reactivity of the MAb to p41/38 to that of another p41-specific MAb (MAb to p41) on immunoblots with purified p41-glutathione S-transferase fusion protein from strains GS and Z29 and GS- and Z29-infected-cell lysates. The two MAbs were tested in an enzyme-linked immunosorbent assay against a panel of synthetic peptides covering the amino acid substitutions between the GS- and Z29-derived p41 proteins, as determined by DNA sequencing of our cloned isolates of the U27 gene. The MAb to p41/38 reacted specifically with a peptide comprising p41 residues 321 to 340 from strain GS. The critical residue in this peptide was serine 328, as the substitution S328N in the Z29 strain rendered the corresponding peptide nonreactive. The p41 S328 marker was present in three of three HHV-6A strains, while four of four sequenced p41 genes from HHV-6B strains had N328. Our findings are of value for the interpretation of previous findings of p41 expression in brains of MS patients and may allow a more detailed analysis of the role of HHV-6 variants in other disorders.

Chlamydia pneumoniae and multiple sclerosis: no significant association

The cause of multiple sclerosis (MS) is unknown. Despite indications from epidemiological and identical-twin studies that MS is infectious, no virus or other infectious agent has been tightly linked to disease. The isolation of Chlamydia pneumoniae from the cerebrospinal fluid (CSF) of MS patients and the detection of both Chlamydia-specific DNA and antibody in MS CSF have been reported. Other analyses of brain and CSF have shown no significant difference in C. pneumoniae-specific DNA or antibody between MS and control subjects. Recent work has revealed intrathecal production of C. pneumoniae-specific IgG in only 24% of MS patients compared with 5% of control patients. More importantly, the major CSF oligoclonal bands from MS patients did not react to C. pneumoniae.

Virally encoded 7TM receptors

A number of herpes- and poxviruses encode 7TM G-protein coupled receptors most of which clearly are derived from their host chemokine system as well as induce high expression of certain 7TM receptors in the infected cells. The receptors appear to be exploited by the virus for either immune evasion, cellular reprogramming, tissue targeting or for cell entry. Through their efficient evolutionary machinery and through in vivo selection performed directly on the human cellular and molecular targets, virus have been able to optimize the encoded receptors for distinct pharmacological profiles to help in various parts of the viral life cyclus. Most of the receptors encoded by human pathogenic virus are still orphan receptors, i.e. the endogenous ligand is unknown. In the few cases where it has been possible to characterize these receptors pharmacologically, they have been found to bind a broad spectrum of either CC chemokines, US28 from human cytomegalovirus, or CXC chemokines, ORF74 from human herpesvirus 8. Nevertheless, US28 has been specifically optimized for recognition of the membrane bound chemokine, fractalkine, conceivably involved in cell-cell transfer of virus; whereas ORF74 among the endogenous CXC chemokines has selected angiogenic chemokines as agonists and angiostatic/modulatory chemokines as inverse agonists. ORF74 possess substantial cell-transforming properties and signals with high constitutive activity through the phospholipase C and MAP kinase pathways. Interestingly, transgenic expression of this single gene in certain lymphocyte cell lineages leads to the development of lesions which are remarkably similar to Kaposi's sarcoma, a human herpesvirus 8 associated disease. Thus, this and other virally encoded 7TM receptors appear to be attractive future drug targets.

Viruses and multiple sclerosis

Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system whose cause is still unknown. Many findings suggest an infectious etiology or, at least, that infectious agents in association with host genetic factors may play a role in the pathogenesis of this disease. Accumulating data, including animal models, human models of virus induced demyelination, epidemiologic, and laboratory findings, demonstrate that viruses and host genetic factors can interact to cause immune-mediated demyelination. While many viruses have been postulated as a possible cause of MS, to date, no "MS virus" has been definitively shown to be associated with this disease. Alternatively, ubiquitous viruses are being considered as the environmental "triggers" that have been postulated to be involved in the MS disease process. We will focus on recent studies with human herpesvirus 6 and MS as how a common virus may be associated with this disorder in a subset of infected individuals.

Multiple sclerosis: current pathophysiological concepts

Multiple sclerosis (MS) is an often disabling disease primarily affecting young adults that exhibits extraordinary clinical, radiological, and pathological heterogeneity. We review the following: (a) known environmental and genetic factors that contribute to MS susceptibility; (b) current knowledge regarding fundamental pathophysiological processes in MS, including immune cell recruitment and entry into the central nervous system (CNS), formation of the plaque, and orchestration of the immune response; (c) descriptive and qualitative distinct pathological patterns in MS and their implications; (d) the evidence supporting the causative role of direct toxins, cell-mediated and humorally mediated immune mechanisms, and the concept of a "primary oligodendrogliopathy" in demyelination and axonal injury; (e) the potential benefits of inflammation; (f) the prospects for remyelination; and (g) therapeutic implications and approaches suggested by putative pathophysiological mechanisms.

Role of viruses in etiology and pathogenesis of multiple sclerosis

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

Infection and the etiology and pathogenesis of multiple sclerosis

Multiple sclerosis (MS) currently defies clinical and scientific definitions, and carries a prognosis that remains practically unchanged despite many years of intensive research. Although the prevailing dogma is that MS is an immune-mediated condition, it fulfills none of the criteria of an autoimmune disease. On the other hand, there is enough significant data to suggest that infectious agents(s) could be involved in either direct damage to the white matter or induce inflammatory responses that secondarily affect the brain. Our goal here is to review the data supporting the possibility that infection has a critical role in the disease, examine the list of potential candidates that have been suggested, and outline an approach regarding the potential role of infectious agents in the etiology and pathogenesis of MS.

Real-time quantitative PCR for human herpesvirus 6 DNA

The diagnosis of human herpesvirus 6 (HHV-6) infection represents a complex issue because the most widely used diagnostic tools, such as immunoglobulin G antibody titer determination and qualitative DNA PCR with blood cells, are unable to distinguish between latent (clinically silent) and active (often clinically relevant) infection. We have developed a new, highly sensitive, quantitative PCR assay for the accurate measurement of HHV-6 DNA in tissue-derived cell suspensions and body fluids. The test uses a 5' nuclease, fluorogenic assay combined with real-time detection of PCR amplification products with the ABI PRISM 7700 sequence detector system. The sensitivity of this method is equal to the sensitivity of a nested PCR protocol (lower detection limit, 1 viral genome equivalent/test) for both the A and the B HHV-6 subgroups and shows a wider dynamic range of detection (from 1 to 10(6) viral genome equivalents/test) and a higher degree of accuracy, repeatability, and reproducibility compared to those of a standard quantitative-competitive PCR assay developed with the same reference DNA molecule. The novel technique is versatile, showing the same sensitivity and dynamic range with viral DNA extracted from different fluids (i.e., culture medium or plasma) or from tissue-derived cell suspensions. Furthermore, by virtue of its high-throughput format, this method is well suited for large epidemiological surveys.

Neuroinvasion by human respiratory coronaviruses

Human coronaviruses (HCoV) cause common colds but can also infect neural cell cultures. To provide definitive experimental evidence for the neurotropism and neuroinvasion of HCoV and its possible association with multiple sclerosis (MS), we have performed an extensive search and characterization of HCoV RNA in a large panel of human brain autopsy samples. Very stringent reverse transcription-PCR with two primer pairs for both viral strains (229E and OC43), combined with Southern hybridization, was performed on samples from 90 coded donors with various neurological diseases (39 with MS and 26 with other neurological diseases) or normal controls (25 patients). We report that 44% (40 of 90) of donors were positive for 229E and that 23% (21 of 90) were positive for OC43. A statistically significant higher prevalence of OC43 in MS patients (35.9%; 14 of 39) than in controls (13.7%; 7 of 51) was observed. Sequencing of nucleocapsid protein (N) gene amplicons revealed point mutations in OC43, some consistently found in three MS patient brains and one normal control but never observed in laboratory viruses. In situ hybridization confirmed the presence of viral RNA in brain parenchyma, outside blood vessels. The presence of HCoV in human brains is consistent with neuroinvasion by these respiratory pathogens. Further studies are needed to distinguish between opportunistic and disease-associated viral presence in human brains.

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.

Several options for antiviral treatment trials in multiple sclerosis--but which targets should be selected?

Involvement of viruses in the pathogenesis of multiple sclerosis (MS) is a long-lived hypothesis, which is has not yet been proven nor refuted. This is partly due to difficulties in the evaluation of diagnostic findings on persistent infections by common viruses such as herpesviruses and endogenous retroviruses. Progress in antiviral treatment of central nervous system (CNS) herpesvirus infections has stimulated controlled trials of long-term therapy with acyclovir and valacyclovir in MS, but conclusive results are not yet available. Other treatment possibilities might include anti-retroviral therapy, as well as attempts to counteract the effects of viruses in triggering attacks of MS following upper respiratory tract infections. Before such trials are initiated, however, further diagnostic evidence of the involvement of target viruses seems warranted.

Central nervous system complications in human herpesvirus-6 infection

Human herpesvirus-6 (HHV-6) is the causative agent of the common childhood infectious disease, exanthem subitum. After the virus was recently isolated from humans, it was found to be closely related to human cytomegalovirus (CMV), and was thus classified within the beta subgroup of human herpesviruses. HHV-6 possesses neurotropism in vitro, and it has been suggested that primary infection can cause complications of the central nervous system (CNS), including febrile seizures and encephalitis/encephalopathy. There is also speculation that the direct invasion of the virus into the CNS may play an important role in causing these neurological complications. Moreover, there are several reports which have suggested an association between HHV-6 and a variety of neurological disorders in adults. This paper will briefly review our virological understanding of the virus, and summarize recent findings regarding HHV-6 as an etiologic agent for CNS infection.

Persisting viruses and autoimmunity

Viral infections can be responsible for the onset and sustaining of autoimmune processes. We discuss how chronic inflammation associated with viral persistence is the prerequisite for initiation of a multi-step process leading to autoimmunity. Firstly, chronic inflammation may favor the priming of autoreactive T cells that have escaped thymic selection and are specific for self-mimicking viral peptides in the periphery. In addition, viral persistence and inflammation can act synergistically to induce and sustain autoimmunity either unveiling cryptic self-epitopes, or favoring determinant spreading, or activating dendritic cells, or promoting constant priming of new autoreactive T cells, or contributing to the efficient generation of effector cells, or, finally, restimulating memory T lymphocytes.

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.

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.

The HHV6 paradox: ubiquitous commensal or insidious pathogen? A two-step in situ PCR approach

BACKGROUND

Progressive multifocal leukoencephalopathy (PML) and multiple sclerosis (MS) are demyelinative diseases of the central nervous system (CNS). PML occurs mostly in individuals with AIDS-impaired immunity and is thought to be caused by JC polyoma virus (JCV). In MS a neurotrophic virus trigger is suspected, but the precise etiology remains unknown. Human herpesvirus 6 (HHV6) is a ubiquitous, commensal and usually benign beta-herpesvirus. Some researchers have found evidence for HHV6 infection in MS plaques and sera. We recently demonstrated a high frequency of cells containing HHV6 genome in PML lesions, as well as co-infection of oligodendrocytes by JCV and HHV6. This suggests that HHV6 may be a co-factor in the etiology of PML, and raises questions about its role in other demyelinative diseases.

OBJECTIVES

To determine the prevalence and cellular localization of HHV6, JCV and HIV-1 infected cells in PML, MS, AIDS and control CNS tissues, and their potential relationship with disease.

STUDY DESIGN

An unconventional, sensitive two-step in situ polymerase chain reaction (ISPCR) procedure was used to amplify and detect HHV6, JCV and HIV-1 genomic DNAs in formalin fixed, paraffin-embedded archival CNS tissues. HHV6, JCV and HIV-1 gene expression was detected by ICC for HHV6 p41 and gp101, JCV large T, and HIV-1 p24 gag and NEF proteins.

RESULTS

A high frequency of HHV6 genome was consistently detected in both PML and MS white matter lesional cells; a peri-lesional concentration was notable. HHV6 was found mainly in oligodendrocytes, but neurons were also infected. HHV6 was present in larger amounts than JCV in PML lesions, while more HIV-1 than HHV6 was present in AIDS. Variable amounts of HHV6 genome were detected in normal, AIDS and other control brains; the frequency of infected cells tended to increase with patient age.

CONCLUSIONS

High concentrations of HHV6 genome in association with PML and MS lesions, open the possibility that HHV6 activation may play a role in the pathogenesis of these demyelinative diseases.

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.

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

BACKGROUND

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

OBJECTIVES

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

RESULTS

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

CONCLUSION

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

Leukotropic herpesviruses in multiple sclerosis

Detection frequency of human herpesvirus 6 (HHV-6) and Epstein Barr virus (EBV) DNA in multiple sclerosis (MS) patients and controls was investigated. DNA of peripheral blood mononuclear leukocytes (PBL) was isolated and amplified by polymerase chain reaction techniques. EBV DNA was detected in all patients and controls. HHV-6 DNA was detected in 7% of MS patients and in 14% of controls. Results are compared with other investigations of HHV-6 DNA in PBL, serum, CSF and brain of patients with MS. Results of the present study and other investigations do not show an association between HHV-6 in PBL and MS. Multiple Sclerosis (2000) 6, 66 - 68

HHV-6, 7 and their related diseases

Human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7) are relatively recently discovered beta-herpesvirus. They are prevalent in the human population. Primary infection of HHV-6 has been associated with exanthem subitum and febrile illness. Little information is known about the clinical characteristics of primary infection with HHV-7, although some cases of exanthem subitum have been linked to it. HHV-6 has been recently recognized as an opportunistic pathogen in patients with HIV infection and in transplant recipients. The techniques now available to detect these two viruses remain limited, though putative roles for HHV-6 and HHV-7 in several diseases linked to viral infection have been reported. This report reviews the current knowledge of HHV-6 and HHV-7 biology and their pathogenesis.

Seroprevalence of viral childhood infections in Eritrea

BACKGROUND

The seroprevalence of viral childhood infections in Africa has not been thoroughly investigated. The relatively recently discovered human parvovirus B19 (B19) and human herpesvirus 6 (HHV-6) have received particularly little attention.

OBJECTIVE

To investigate the seroprevalence of viral childhood infections in different Eritrean populations and to define groups at high risk for infection.

STUDY DESIGN

Five population groups in Eritrea have been examined to define the prevalence of specific antibodies to several childhood viruses. The study population of more than 400 persons consisted of children, pregnant women, female sex workers and members of a secluded tribe called Rashaida.

RESULTS

All groups showed a high prevalence of antibodies to measles and HHV-6 (> 85%). For rubella, the seroprevalence was very high in all adult groups (93-99%) except the Rashaida group (71%). The mumps prevalence was surprisingly low in the Rashaida group (29%) compared to 46-85% in the other adults. Late encounter of mumps and rubella was also observed among the Rashaidas. The pattern of antibodies to B19 showed a higher seroprevalence in all groups (56-91%) compared to what has been reported from the western world.

CONCLUSION

The findings represent what might be expected in an unvaccinated population. The exception was the Rashaidas, which had low seroprevalences and late encounter of mumps and rubella. This is of importance because it makes this tribe vulnerable to these infections, which are associated with complications when acquired in adult age. Also noteworthy is the high frequency of antibodies to HHV-6 and particularly B19 in all groups, indicative of an early encounter of both these viruses.

Clinical characteristics of febrile convulsions during primary HHV-6 infection

OBJECTIVE

To clarify clinical characteristics of children with febrile convulsions during primary human herpesvirus 6 (HHV-6) infection.

SUBJECTS AND METHODS

The clinical characteristics of first febrile convulsion were compared between those with and without primary HHV-6 infection in 105 children. HHV-6 infection was verified by culture or acute/convalescent anti-HHV-6 antibody titres.

RESULTS

Primary infection with HHV-6 was seen in 21 of 105 patients with febrile convulsions (3 upper respiratory infection, 1 lower respiratory infection, and 17 exanthem subitum). 13 of 23 patients < 1 year, 19 of 79 patients with first febrile convulsion, and 2 of 15 with second convulsion were infected with HHV-6. The median age of patients with first febrile convulsion and HHV-6 was significantly lower than those without infection. The frequency of clustering seizures, long lasting seizures, partial seizures, and postictal paralysis was significantly higher among those with primary HHV-6 infection than among those without. The frequency of atypical seizures in 19 patients with first febrile convulsion associated with primary infection was significantly higher than in 60 patients without primary infection. The frequency in infants younger than 1 year of age was also significantly higher than that in 10 age matched infants without primary infection.

CONCLUSIONS

These findings suggest that primary infection with HHV-6 is frequently associated with febrile convulsions in infants and young children and that it often results in the development of a more severe form of convulsions, such as partial seizures, prolonged seizures, and repeated seizures, and might be a risk factor for subsequent development of epilepsy.

Infectious etiology in multiple sclerosis: the debate continues

‘Demonstrating Infectious Cause: Viral and Bacterial Infections in MS and Related Disorders’ was held in Brighton, UK, 23–25 August 1999.

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.

Chronic fatigue syndrome: new insights and old ignorance

Chronic fatigue syndrome (CFS) is a condition characterized by impairment of neurocognitive functions and quality of sleep and of somatic symptoms such as recurrent sore throat, muscle aches, arthralgias, headache, and postexertional malaise. A majority of patients describe an infectious onset but the link between infections and CFS remains uncertain. Findings show an activation of the immune system, abberations in several hypothalamic-pituitary axes and involvement of other parts of the central nervous system. The origin is bound to be complex and it may well be that the solution will come together with a more generally altered view about mind-body dualism, and the concept of illness and disease.

Viral Hyperinfection of the Central Nervous System and High Mortality After Hematopoietic Stem Cell Transplantation for Treatment of Theiler’s Murine Encephalomyelitis Virus-Induced Demyelinating Disease

Theiler’s murine encephalomyelitis virus (TMEV) establishes a persistent infection in the central nervous system (CNS) leading to an inflammatory demyelinating disease of the CNS in which the histology and clinical course is similar to multiple sclerosis (MS). Disease pathogenesis is primarily due to T-cell–mediated destruction of myelin, which has been attributed to cytopathic effects of the virus, but immune-mediated destruction of myelin mediated via both virus-specific and myelin-specific T cells appear to play the major role. To determine if bone marrow transplantation would be an effective therapy for a virus-initiated autoimmune disease and to better separate viral cytopathic effects from immune-mediated demyelination, we ablated the immune system of TMEV-infected animals with 1,100 cGy total body irradiation, and then the animal’s immunity was reconstituted by transplantation of disease-susceptible SJL/J mice with syngeneic marrow or disease-susceptible DBA/2J with marrow from disease-resistant (C57Bl/6 × DBA/2)F1 (B6D2) donors. Hematopoietic transplant performed after onset of disease resulted in 42% mortality in SJL/J syngeneic transplants, 47% mortality in diseased DBA2 recipients restored with marrow from naive B6D2 donors, and 12% in diseased DBA2 recipients receiving marrow from B6D2 donors previously infected with TMEV. Delayed type hypersensitivity (DTH) to both virion and myelin proteins was decreased in surviving mice that underwent transplantation; however, CNS viral titers were significantly elevated compared with nontransplanted controls. We conclude that a functional immune system with appropriate T-cell responses are important in prevention of lethal cytopathic CNS effects from TMEV. Relevant to the clinical use of bone marrow transplantation, attempts to ablate the immune system in viral-mediated immune diseases or virus-initiated autoimmune disease may have acute and lethal consequences. Our results raise concern about the attempted use of autologous hematopoietic transplantation in patients with MS, an autoimmune disease with a suspected virus etiology, particularly if the graft is aggressively depleted of lymphocytes.

Human herpesvirus 7

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

The association of the human herpesvirus-6 and MS

Given the clinical and pathological nature of Multiple Sclerosis (MS), a viral infection has long been hypothesized as part of the etiology. In this study we investigated the possibility that the human herpesvirus-6 (HHV-6) is present in a dormant or active phase in the tissue of MS patients, specifically oligodendrocytes. Using PCR assays of MS and non-MS brain sections with primers prepared against the HHV-6 structural protein 101, the results demonstrated that 36% of MS brains were positive for the virus, while 13.5% of non-MS brains were positive. Antibody to the HHV-6 structural protein was also used in immunohistochemical experiments in brain tissue. 47% (7/15) of MS brains were positive for HHV-6, whereas 0/16 controls were positive. In addition, MS patients demonstrated high immune reactivity to this virus, even when compared to auto-immune diseases, which might cause polyclonal activation. Sera obtained from MS and control patients revealed that the IgM response to the HHV-6 virus was significantly elevated in 80% patients compared to 16% non-MS controls, P<.001. The above experiments strongly suggest that a significant number of MS brain samples contain HHV-6 antigens and genomic fragments in a dormant or active phase compared to control specimens and that MS patients mount a brisk, early IgM response.

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.

Similar humoral and cellular immunological reactivities to human herpesvirus 6 in patients with multiple sclerosis and controls

Several studies have suggested an association between human herpesvirus 6 (HHV-6) and multiple sclerosis (MS). We have previously studied intrathecal production of antibody to lymphotropic herpesviruses in MS patients and the presence of human herpesvirus 1 to 7 DNAs in cerebrospinal fluid (CSF). In the present study anti-HHV-6 immunoglobulin M (IgM) in serum and anti-HHV-6 IgG subclasses in serum and CSF were examined and the lymphoproliferative response to HHV-6 was analyzed. The PCR examination was refined by purifying DNA from CSF and retesting the samples for HHV-6 DNA. There were no statistically significant differences between the groups concerning IgM positivity, distribution of IgG subclasses, or lymphoproliferative response to HHV-6. The purification of DNA increased the number of PCR-positive samples from 0 of 71 to 4 of 68. The study does not give additional support to the possibility that HHV-6 is a common cause of MS, but a role for the virus in a subset of patients cannot be excluded.

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.

Progress in determining the causes and treatment of multiple sclerosis

The cause of multiple sclerosis remains unknown after more than a century of study. Unconfirmed work has once more indicated that a viral infection may be important in the aetiology of the disease, and there is considerable evidence for an important genetic influence on disease susceptibility. The clinical course is as variable as that of any disease in medicine. Studies using serial magnetic resonance imaging have helped to define the disease course and response to experimental therapies. Although the predominant pathological characteristic is myelin loss with preservation of axons, some studies recall classic descriptions that irreversible axonal destruction may occur, perhaps even in the early stages of the illness. There are now several, partially effective therapies for relapsing forms of multiple sclerosis and here I review progress in determining the timing and course of the illness and the steps that need to be taken to identify more effective treatments for this disease.

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.

Fine mapping of an apparently targeted latent human herpesvirus type 6 integration site in chromosome band 17p13.3

An unusually high level of latent HHV-6 infection has been documented in the peripheral blood and/or bone marrow cells of a small group of patients with predominantly malignant lymphoid disorders, and in at least one healthy individual. We have shown previously in peripheral blood mononuclear cells (PBMCs) of three patients, two with a history of lymphoma and one with multiple sclerosis, a specific target site for latent integration of the full-length HHV-6 viral genome on the distal short arm of chromosome 17, in band p13.3. Fluorescence in situ hybridization (FISH) procedures were used to map more precisely the location of the viral integration site in one of those patients, relative to two known oncogenes mapped previously, namely CRK, and the more telomeric ABR oncogene. It is shown that the HHV-6 integration site is located at least 1,000 kb telomeric of ABR, and is very likely to map close to or within the telomeric sequences of 17p. This finding is significant given that human telomeric-like repeats flank the terminal ends of the HHV-6 genome. Cytogenetic studies showed evidence of karyotype instability in the peripheral blood cells infected latently.

Herpesviruses--a rationale for antiviral treatment in multiple sclerosis

In multiple sclerosis (MS), the extensive and long lasting search for viruses or other pathogens has hitherto failed to identify a common etiological agent. However, the beneficial effects by interferon-beta treatment in MS, although suggested to depend mainly on immunomodulation, might lend support to a viral involvement in the pathogenesis. The human herpesviruses have attracted interest since their recurrent modes of infection share some similarity with the relapsing-remitting course of MS, most members are readily detected within the brain, and several of these viruses may induce demyelination within the central nervous system in human hosts as well as in animal models. Accumulated diagnostic and epidemiological data are compatible with a role for the herpesviruses as possible cofactors rather than etiological agents, and recent studies showing early neuronal damage in MS patients focus attention on the neurotropic alpha-herpesviruses. Antiviral treatment trials with safe and effective drugs such as valaciclovir offer a possibility of testing the hypotheses concerning herpesviral involvement in MS.

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.

Molecular characterization and placental expression of HERV-W, a new human endogenous retrovirus family

The multiple sclerosis-associated retrovirus (MSRV) isolated from plasma of MS patients was found to be phylogenetically and experimentally related to human endogenous retroviruses (HERVs). To characterize the MSRV-related HERV family and to test the hypothesis of a replication-competent HERV, we have investigated the expression of MSRV-related sequences in healthy tissues. The expression of MSRV-related transcripts restricted to the placenta led to the isolation of overlapping cDNA clones from a cDNA library. These cDNAs spanned a 7.6-kb region containing gag, pol, and env genes; RU5 and U3R flanking sequences; a polypurine tract; and a primer binding site (PBS). As this PBS showed similarity to avian retrovirus PBSs used by tRNATrp, this new HERV family was named HERV-W. Several genomic elements were identified, one of them containing a complete HERV-W unit, spanning all cDNA clones. Elements of this multicopy family were not replication competent, as gag and pol open reading frames (ORFs) were interrupted by frameshifts and stop codons. A complete ORF putatively coding for an envelope protein was found both on the HERV-W DNA prototype and within an RU5-env-U3R polyadenylated cDNA clone. Placental expression of 8-, 3.1-, and 1.3-kb transcripts was observed, and a putative splicing strategy was described. The apparently tissue-restricted HERV-W long terminal repeat expression is discussed with respect to physiological and pathological contexts.

EBV-Induced Expression and HLA-DR-Restricted Presentation by Human B Cells of αB-Crystallin, a Candidate Autoantigen in Multiple Sclerosis

The development of multiple sclerosis is most likely influenced by autoimmune responses to central nervous system myelin proteins as well as by infections with common viruses such as EBV and human herpesvirus-6. However, much remains to be established on how these factors interact. In this study, we show that upon EBV infection, human B cells start to express αB-crystallin, a small stress protein that was identified previously as an immunodominant Ag of CNS myelin in multiple sclerosis patients. EBV-induced expression of αB-crystallin in B cells leads to HLA-DR-restricted presentation of the protein and to activation of proinflammatory αB-crystallin-specific Th cells. While αB-crystallin is present in EBV-infected human B cells, the protein is absent from human lymphoid tissues under normal conditions. This is in sharp contrast to other stress proteins such as heat-shock protein (hsp)27 and hsp60 that are ubiquitously expressed in these tissues. In addition, the absence of αB-crystallin from lymphoid tissues in humans is unique as compared with other mammals. All other species examined, including rodents, sheep, and primates, showed constitutive expression of αB-crystallin in secondary lymphoid tissues and sometimes even in the thymus. Since constitutive lymphoid expression most likely results in immunologic tolerance, such a state of tolerance to αB-crystallin can be expected for all of these species, but not for humans. When taken together, our data provide evidence for a novel mechanism by which common viral infections can trigger myelin-directed autoimmunity in a way that is unique for humans.

Trafficking to the plasma membrane of the seven-transmembrane protein encoded by human herpesvirus 6 U51 gene involves a cell-specific function present in T lymphocytes

The sequence of human herpesvirus 6 (HHV-6) U51 open reading frame predicts a protein of 301 amino acid residues with seven transmembrane domains. To identify and characterize U51, we derived antipeptide polyclonal antibodies and developed a transient expression assay. We ascertained that U51 was synthesized in cord blood mononuclear cells infected with either variant A- or variant B-HHV-6 and was transported to the surface of productively infected cells. When synthesized in transient expression systems, U51 intracellular trafficking was regulated in a cell-type-dependent fashion. In human monolayer HEK-293 and 143tk- cells, U51 accumulated predominantly in the endoplasmic reticulum and failed to be transported to the cell surface. In contrast, in T-lymphocytic cell lines J-Jhan, Molt-3, and Jurkat, U51 was successfully transported to the plasma membrane. We infer that transport of U51 to the cell surface requires a cell-specific function present in activated T lymphocytes and T-cell lines.

Human herpesvirus 6 latently infects early bone marrow progenitors in vivo

We have studied the in vivo tropism of human herpesvirus 6 (HHV-6) for hemopoietic cells in patients with latent HHV-6 infection. Having used a variety of cell purification, molecular, cytogenetic, and immunocytochemical procedures, we report the first evidence that HHV-6 latently infects early bone marrow progenitor cells and that HHV-6 may be transmitted longitudinally to cells which differentiate along the committed pathways.