Three new human herpesviruses (HHV6, 7, and 8)

A rapid plate assay for the screening of inhibitors against herpesvirus DNA polymerases and processivity factors

Kaposi's sarcoma-associated herpesvirus (KSHV) is a newly identified human pathogen with tumorigenic potential. The DNA polymerase (Pol-8) and processivity factor (PF-8) of KSHV were cloned recently. It was shown that PF-8 forms specifically a complex with Pol-8 in vitro and allows it to synthesize fully-extended DNA. Since both Pol-8 and PF-8 are apparently essential for viral DNA replication and since they cannot be substituted by any other cellular or viral proteins, they are potentially excellent antiviral targets. The development of a mechanistic plate assay is now described, which is suitable for rapid high-throughput screening of antiviral agents against Pol-8 and PF-8. The assay allows the measurement of not only total DNA synthesis activity (i.e. nucleotide incorporation) but also processivity (i.e. fully-extended DNA product). In this plate assay, any of the screen-compounds with an inhibitory effect against the total DNA synthesis activity and/or the processivity could be potential antiviral agents that target Pol-8 and/or PF-8. Particularly, since PF-8 is highly specific for Pol-8, the discovery of inhibitory agents against PF-8 may lead to specific antiviral therapies with minimal toxicity to host cells. This assay should be suitable for screening for inhibitory compounds against polymerases and processivity factors of other herpesviruses as well.

Human herpesviruses in primary ocular lymphoma

Several human lymphotropic herpesviruses have been found in certain lymphoproliferative disorders and implicated as possible etiologic factors or as modulating elements of the diseases. To assess a possible association of the human herpesviruses with lymphomas arising from mucosa-associated lymphoid tissue (MALT), we evaluated the presence of four human herpesviruses, Epstein-Barr virus (EBV), human herpesvirus 6 (HHV-6), HHV-7, and HHV-8, in the biopsied specimens from 14 patients with primary ocular MALT lymphomas. EBV DNA sequences were detected in four specimens by polymerase chain reaction (PCR), and four cases were positive for HHV-6 DNA. In situ hybridization showed that three and two of 14 cases were positive for EBV mRNA and HHV-6 DNA, respectively. Neither HHV-7 nor HHV-8 sequences could be detected by PCR. These findings would stimulate further investigation as to the involvement of these lymphotropic viruses in the pathogenesis of a subset of low-grade primary ocular lymphomas.

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

Aggressive Kaposi's sarcoma in a 6-month-old African infant: case report and review of the literature

Kaposi's sarcoma (KS), known to exist in Africa for a century now, was rare in children and unknown in the newborn. With the onset of the HIV/AIDS epidemic, a more aggressive, disseminated type of KS (AKS) was recognized. Recently KS was diagnosed in a 6-month-old infant in Tanzania. Data support the notion that HHSV8 infectivity can be potentiated with HIV infection and thus produce multiple lesions in different anatomical sites early in life. Furthermore, the available evidence would suggest a nonsexual route of HHSV8 infection, possibly from mother to fetus.

Antibodies to human herpes virus type 8 (HHV8) in general population and in individuals at risk for sexually transmitted diseases in Western Sicily

BACKGROUND

Human herpes virus 8 (HHV8) appears to be the primary aetiologic agent of Kaposi sarcoma (KS). To study the distribution of HHV8, a seroepidemiological study was carried out in western Sicily, where a high incidence rate of classical KS is well documented.

METHODS

A total of 970 sera of healthy human immunodeficiency virus (HIV) negative individuals of general population (1-70 years old) and 742 sera of individuals in different risk groups for HIV infection were evaluated by means of an indirect immunofluorescence assay able to detect antibodies to lytic and latent HHV8 antigens.

RESULTS

Crude seroprevalence to HHV8 antigens was 11.5% in the general population, and it increased significantly with age from 6% under age 16 to 22% after age 50. Significantly higher HHV8 seroprevalence rates were detected among HIV positive and negative homosexual men (62% and 22%, respectively), men who had sex with prostitutes (40% and 29%, respectively); female prostitutes (42% and 30%, respectively), and clients at a sexually transmitted disease clinic (male: 60% and 33%, respectively, female: 63% and 43%, respectively). In contrast, heterosexual intravenous drug users had seroprevalence rates comparable to those found in the general population.

CONCLUSIONS

The results suggest that HHV8 infection is widespread in Western Sicily. The high seroprevalence in individuals with high risk sexual activity point to the role of sexual behaviour in the transmission of the infection in adults, whereas the detection of antibodies in younger population (under 16 years old) is suggestive of a non-sexual route of transmission, probably occurring during childhood by close personal contact.

The herpesvirus proteases as targets for antiviral chemotherapy

Viruses of the family Herpesviridae are responsible for a diverse set of human diseases. The available treatments are largely ineffective, with the exception of a few drugs for treatment of herpes simplex virus (HSV) infections. For several members of this DNA virus family, advances have been made recently in the biochemistry and structural biology of the essential viral protease, revealing common features that may be possible to exploit in the development of a new class of anti-herpesvirus agents. The herpesvirus proteases have been identified as belonging to a unique class of serine protease, with a Ser-His-His catalytic triad. A new, single domain protein fold has been determined by X-ray crystallography for the proteases of at least three different herpesviruses. Also unique for serine proteases, dimerization has been shown to be required for activity of the cytomegalovirus and HSV proteases. The dimerization requirement seriously impacts methods needed for productive, functional analysis and inhibitor discovery. The conserved functional and catalytic properties of the herpesvirus proteases lead to common considerations for this group of proteases in the early phases of inhibitor discovery. In general, classical serine protease inhibitors that react with active site residues do not readily inactivate the herpesvirus proteases. There has been progress however, with activated carbonyls that exploit the selective nucleophilicity of the active site serine. In addition, screening of chemical libraries has yielded novel structures as starting points for drug development. Recent crystal structures of the herpesvirus proteases now allow more direct interpretation of ligand structure-activity relationships. This review first describes basic functional aspects of herpesvirus protease biology and enzymology. Then we discuss inhibitors identified to date and the prospects for their future development.

Co-infection of HHV-6 and HHV-8 is rare in primary effusion lymphoma

The presence and distribution of Epstein-Barr virus (EBV), as well as human herpesvirus-6 and-8 (HHV-6 and HHV-8) was investigated by polymerase chain reaction in 191 samples from a variety of lymphoproliferative disorders. HHV-6 DNA was detected in 18% (30 of 169) of non-HHV-8 related lymphoproliferative disorders, with the highest frequency in AIDS-related lymphomas (8 of 25, 32%). In contrast, HHV-6 DNA was present in less than 5% (1 of 22) of HHV-8 related lymphoproliferative disorders [21 primary effusion lymphomas (PEL), and 1 cases of Castleman disease]. As compared to HHV-6, EBV DNA was frequently detected in PEL (11 of 19 samples, 58%). This study suggests that transformation to PEL is not enhanced by HHV-6, furthermore HHV-6 and -8 may interfere with each other.

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.

Viral and fungal infections of the oral cavity in immunocompetent patients

Oral lesions are easily visualized and often are signs of systemic diseases. Clinical diagnosis of viral and fungal infections can sometimes be confusing because many lesions will have similar clinical presentations. This article reviews the more common viral- and fungal-associated lesions found in the oral cavity in immunocompetent individuals. Differential diagnoses for the oral lesions are discussed and treatment options are proposed.

Cell adhesion molecules in the pathogenesis of and host defence against microbial infection

Eukaryotic cell adhesion molecules (CAMs) are used by various cells and extracellular molecules in host defence against infection. They are involved in many processes including recognition by circulating phagocytes of a site of inflammation, transmigration through the endothelial barrier, diapedesis through basement membrane and extracellular matrix, and release of effector mechanisms at the infected site. CAMs involved in leucocyte-endothelial cell interaction include the selectins, integrins, and members of the immunoglobulin superfamily. However, CAMs are also used by various microorganisms (protozoa, fungi, bacteria, and viruses) during their pathogenesis. For example, bacteria that utilise CAMs include Mycobacterium tuberculosis, Listeria monocytogenes, Yersinia spp, enteropathogenic Escherichia coli, Shigella spp, Neisseria spp, Bordetella spp, and Borrelia burgdorferi. In addition, CAMs are involved in the pathogenetic effects of the RTX toxins of Pasteurella haemolytica, Actinobacillus actinomycetemcomitans, and the superantigen exotoxins of Staphylococcus aureus and Streptococcus pyogenes. A recurrent and topical theme of potential importance within the bacterial group is the intimate relation between CAMs, bacterial protein receptors, and type III secretion systems. For example, the IpaBCD protein complex is secreted by the type III system of Shigella flexneri and interacts with alpha 5 beta 1 integrin on the eukaryotic cell surface, followed by Rho mediated internalisation; this illustrates the relevance of cellular microbiology. CAMs might prove to be novel therapeutic targets. Comparative genomics has provided the knowledge of shared virulence determinants among diverse bacterial genera, and will continue to deepen our understanding of microbial pathogenesis, particularly in the context of the interaction of prokaryotic and eukaryotic molecules.

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.

The risk of using baboons as transplant donors. Exogenous and endogenous viruses

African nonhuman primates harbor several exogenous and endogenous retroviruses which deserve further consideration in the transplant setting. In particular, simian foamy viruses (SFV), simian T-cell lymphotropic virus (STLV), baboon endogenous virus (BaEV), and simian endogenous retrovirus (SERV) are all carried by baboons and may be transmitted to humans by transplantation. We have found baboons to have high seroprevalence rates to both SFV and STLV, and molecular and serologic methods have been developed to detect such agents. In addition, current nonhuman primate breeding programs have thus far not focused on eliminating these viruses. In summary, the close genetic relationship with humans and number of persistent viral infections in baboons translates into a much greater infectious disease risk when compared to that of other domesticated species.

Molecular piracy: the viral link to carcinogenesis

The vast majority of the human experience with viral infections is associated with acute symptoms, such as malaise, fever, chills, rhinitis and diarrhea. With this acute or lytic phase, the immune system mounts a response and eliminates the viral agent while acquiring antibodies to that specific viral subtype. With latent or chronic infections, the viral agent becomes incorporated into the human genome. Viral agents capable of integration into the host's genetic material are particularly dangerous and may commandeer the host's ability to regulate normal cell growth and proliferation. The oncogenic viruses may immortalize the host cell, and facilitate malignant transformation. Cell growth and proliferation may be enhanced by viral interference with tumor suppressor gene function (p53 and pRb). Viruses may act as vectors for mutated proto-oncogenes (oncogenes). Overexpression of these oncogenes in viral-infected cells interferes with normal cell function and allows unregulated cell growth and proliferation, which may lead to malignant transformation and tumour formation. Development of oral neoplasms, both benign and malignant, has been linked to several viruses. Epstein-Barr virus is associated with oral hairy leukoplakia, lymphoproliferative disease, lymphoepithelial carcinoma, B-cell lymphomas, and nasopharyngeal carcinoma. Human herpesvirus-8 has been implicated in all forms of Kaposi's sarcoma, primary effusion lymphomas, multiple myeloma, angioimmunoblastic lymphadenopathy, and Castleman's disease. Human herpesvirus-6 has been detected in lymphoproliferative disease, lymphomas, Hodgkin's disease, and oral squamous cell carcinoma. The role of human papillomavirus in benign (squamous papilloma, focal epithelial hyperplasia, condyloma acuminatum, verruca vulgaris), premalignant (oral epithelial dysplasia), and malignant (squamous cell carcinoma) neoplasms within the oral cavity is well recognized. Herpes simplex virus may participate as a cofactor in oral squamous cell carcinoma development by enhancing activation, amplification, and overexpression of pre-existing oncogenes within neoplastic tissues. Because of the integral role of viruses in malignant transformation of host cells, innovative antiviral therapy may prevent tumour development, involute neoplastic proliferations, or arrest malignant progression.

Propagation and characterization of human herpesvirus-7 (HHV-7) isolates in a continuous T-lymphoblastoid cell line (SupT1)

After initial culture of HHV-7 in PHA-stimulated human cord blood mononuclear cells (HCBMC), six HHV-7 isolates were propagated successfully in an immature continuous T-lymphoblastoid cell line SupT1. All six isolates infected efficiently the SupT1 cells, and the infected cells became grossly enlarged and multinucleated 7-21 days post-infection. Various stages of HHV-7 morphogenesis were detected. Cell-free supernatants from HHV-7-infected SupT1 cells were infectious to HCBMC as well as to SupT1 cells. The HHV-7-infected SupT1 and HCBMC cell lysates contained more infectious virus than the centrifuged cell culture fluid supernates from the same culture. The HHV-7 isolates H7-2, H7-3, JHC, and JB, concentrated 500 times, had average infectivity titers of 10(3.0) TCID50/ml while strains H7-4 and KHR titered approximately 1-2 logs higher. When all six HHV-7 isolates were propagated in SupT1 and culture fluid supernatants were examined 14-21 days post-infection by negative stain electron microscopy they contained an average of 1.9 x 10(9) virus particles/liter. IFA and ELISA, using HHV-7/SupT1 cell lysate as an antigen, seem to correlate well in detecting high and low HHV-7 antibody in sera from chronic fatigue patients and healthy donors as controls. HHV-7 from SupT1 cell culture was free of HHV-6 and other human herpesviruses as tested by PCR, and the HHV-7 PCR signal was still strong when the viral preparation was diluted to 4.82 x 10(2) genome copies. Since HCBMC are expensive to obtain and available in only small amounts, it is difficult to obtain large quantities of HHV-7 antigen. On the other hand, the SupT1 cell is an excellent source to produce consistently sufficient quantities of HHV-7 for purification studies, development of immunodiagnostics, in vivo infectivity studies, evaluation of antiviral drugs, and molecular biological studies.

Cloning and functional analysis of Kaposi's sarcoma-associated herpesvirus DNA polymerase and its processivity factor

Kaposi's sarcoma-associated herpesvirus (KSHV), or human herpesvirus 8, is a newly identified virus with tumorigenic potential. Here, we cloned and expressed the DNA polymerase (Pol-8) of KSHV and its processivity factor (PF-8). Pol-8 bound specifically to PF-8 in vitro. Moreover, the DNA synthesis activity of Pol-8 was shown in vitro to be strongly dependent on PF-8. Addition of PF-8 to Pol-8 allowed efficient synthesis of fully extended DNA products corresponding to the full-length M13 template (7,249 nucleotides), whereas Pol-8 alone could incorporate only several nucleotides. The specificity of PF-8 and Pol-8 for each other was demonstrated by their inability to be functionally replaced by the DNA polymerases and processivity factors of herpes simplex virus 1 and human herpesvirus 6.

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

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

Geography of AIDS-associated Kaposi's sarcoma in Europe

BACKGROUND

Classical Kaposi's sarcoma (KS) is about four times more common in southern Europeans than in northern Europeans.

OBJECTIVE

To describe the epidemiology of AIDS-associated KS (AIDS-KS) in Europe and to determine whether it occurs with increased frequency in southern Europe.

METHODS

Analysis of the 'European non-aggregate AIDS data set', as of September 1995. Countries with a cumulative total of > or = 50 KS cases as the presenting manifestation of AIDS were included. Homosexual men were excluded from south versus non-south comparisons because of possible confounding effects due to their route of HIV transmission.

RESULTS

KS was the presenting manifestation of AIDS for 13.3% (16,367 out of 122,679) of men and 2% (491 out of 24,826) of women. In all countries, the risk for KS was higher in individuals who acquired HIV infection via sexual rather than parenteral transmission. Among AIDS patients, there is little difference by sex in the risk of KS in injecting drug users (IDU) or transfusion recipients. The percentage with KS increased with age among homosexual and bisexual men, from 10% in the age group 15-19 years to 23% in the age group 30-39 years. In all countries, the percentage with KS declined over time. The risk of KS was not significantly higher in southern Europe. The percentage with KS in southern Europe was slightly lower than in northern Europe (P > 0.1) in male IDU (1.8% versus 2.1%), and only slightly higher (P > 0.1) in female IDU (1.5% versus 1.1%), in male transfusion recipients (3.5% versus 3.0%), in female transfusion recipients (2.4% versus 2.3%), and in both heterosexual men (7.5% versus 6.2%) and women (2.0% versus 1.6%) excluding those originating from countries where heterosexual HIV transmission is frequent.

CONCLUSIONS

The strong geographic predilection described for classical KS in southern Europe was not seen for AIDS-KS. If KS is caused by a viral infection in an immunodeficient host, our findings suggest the geographical variations in classical KS are not due to variation in prevalence of the causative virus but may be due to geographical variations in the prevalence of a form of mild immunodeficiency.

In situ polymerase chain reaction-based localization studies support role of human herpesvirus-8 as the cause of two AIDS-related neoplasms: Kaposi's sarcoma and body cavity lymphoma

Several lines of investigation point to a new herpesvirus, human herpesvirus-8 (HHV-8), as the cause of two different neoplasms seen in AIDS patients-Kaposi's sarcoma (KS) and body cavity B cell lymphoma. If this virus is the etiological agent, rather than another opportunistic infectious agent, it should be present in the earliest detectable clinical lesions on a temporal basis, and localize to specific target cells in a spatial pattern consistent with tumorigenic pathways. In this study, we take advantage of the clinical accessibility to biopsy early (patch stage) skin lesions of KS to address the temporal issue, combined with in situ PCR and dual immunostaining using a marker identifying malignant cells, to address the spatial localization issue. 21 different tissue samples were subjected to PCR analysis and in situ PCR with and without simultaneous immunostaining. In normal skin from healthy individuals, no HHV-8 DNA was detected by PCR or in situ PCR. However, in all PCR-positive tissues, distinct and specific in situ PCR staining was observed. In four different patch stage KS lesions, in situ PCR staining localized to nuclei of endothelial cells and perivascular spindle-shaped tumor cells. Later stage KS lesions (plaques and nodules) revealed additional positive cells, including epidermal keratinocytes (four of five), and eccrine epithelia (two of four). These patterns were nonrestricted to skin, as pulmonary KS also revealed HHV-8-specific infection of endothelial cells and KS tumor cells, as well as epithelioid pneumocytes (two of two). In body cavity B cell lymphoma by dual staining, HHV-8 was present in malignant tumor cells (EMA immunostained positive) and not in reactive lymphocytes. These results reveal an early temporal onset and nonrandom tissue and cellular distribution pattern for HHV-8 infection that is consistent with a causal link between this DNA virus and two AIDS-related neoplasms.