Epstein-Barr virus replication in oropharyngeal epithelial cells

Kaposi's sarcoma-associated herpesvirus ORF18 and ORF30 are essential for late gene expression during lytic replication

Kaposi's sarcoma-associated herpesvirus (KSHV) is associated with several human malignances. As saliva is likely the major vehicle for KSHV transmission, we studied in vitro KSHV infection of oral epithelial cells. Through infection of two types of oral epithelial cells, normal human oral keratinocytes (NHOKs) and papilloma-immortalized human oral keratinocyte (HOK16B) cells, we found that KSHV can undergo robust lytic replication in oral epithelial cells. By employing de novo lytic infection of HOK16B cells, we studied the functions of two previously uncharacterized genes, ORF18 and ORF30, during the KSHV lytic cycle. For this purpose, an ORF18-deficient virus and an ORF30-deficient virus were generated using a mutagenesis strategy based on bacterial artificial chromosome (BAC) technology. We found that neither ORF18 nor ORF30 is required for immediately early or early gene expression or viral DNA replication, but each is essential for late gene expression during both de novo lytic replication and reactivation. This critical role of ORF18 and ORF30 in late gene expression was also observed during KSHV reactivation. In addition, global analysis of viral transcripts by RNA sequencing indicated that ORF18 and ORF30 control the same set of viral genes. Therefore, we suggest that these two viral ORFs are involved in the same mechanism or pathway that coregulates the viral late genes as a group.

IMPORTANCE

While KSHV can infect multiple cell types in vitro, only a few can support a full lytic replication cycle with progeny virions produced. Consequently, KSHV lytic replication is mostly studied through reactivation, which requires chemicals to induce the lytic cycle or overexpression of the viral transcriptional activator, RTA. In this study, we present a robust de novo lytic infection system based on oral epithelial cells. Using this system, we demonstrate the role of two viral ORFs, ORF18 and ORF30, in regulating viral gene expression during KSHV lytic replication. As the major route of KSHV transmission is thought to be via saliva, this new KSHV lytic replication system will have important utility in the field.

Is murine gammaherpesvirus-68 (MHV-68) a suitable immunotoxicological model for examining immunomodulatory drug-associated viral recrudescence?

Immunosuppressive agents are used for treatment of a variety of autoimmune diseases including rheumatoid arthritis (RA), systemic lupus erythematosis (SLE), and psoriasis, as well as for prevention of tissue rejection after organ transplantation. Recrudescence of herpesvirus infections, and increased risk of carcinogenesis from herpesvirus-associated tumors are related with immunosuppressive therapy in humans. Post-transplant lymphoproliferative disorder (PTLD), a condition characterized by development of Epstein Barr Virus (EBV)-associated B-lymphocyte lymphoma, and Kaposi's Sarcoma (KS), a dermal tumor associated with Kaposi Sarcoma-associated virus (KSHV), may develop in solid organ transplant patients. KS also occurs in immunosuppressed Acquired Immunodeficiency (AIDS) patients. Kaposi Sarcoma-associated virus (KSHV) is a herpes virus genetically related to EBV. Murine gammaherpes-virus-68 (MHV-68) is proposed as a mouse model of gammaherpesvirus infection and recrudescence and may potentially have relevance for herpesvirus-associated neoplasia. The pathogenesis of MHV-68 infection in mice mimics EBV/KSHV infection in humans with acute lytic viral replication followed by dissemination and establishment of persistent latency. MHV-68-infected mice may develop lymphoproliferative disease that is accelerated by disruption of the immune system. This manuscript first presents an overview of gammaherpesvirus pathogenesis and immunology as well as factors involved in viral recrudescence. A description of different types of immunodeficiency then follows, with particular focus on viral association with lymphomagenesis after immunosuppression. Finally, this review discusses different gammaherpesvirus animal models and describes a proposed MHV-68 model to further examine the interplay of immunomodulatory agents and gammaherpesvirus-associated neoplasia.

Deficient EBV-specific B- and T-cell response in patients with chronic fatigue syndrome

Epstein-Barr virus (EBV) has long been discussed as a possible cause or trigger of Chronic Fatigue Syndrome (CFS). In a subset of patients the disease starts with infectious mononucleosis and both enhanced and diminished EBV-specific antibody titers have been reported. In this study, we comprehensively analyzed the EBV-specific memory B- and T-cell response in patients with CFS. While we observed no difference in viral capsid antigen (VCA)-IgG antibodies, EBV nuclear antigen (EBNA)-IgG titers were low or absent in 10% of CFS patients. Remarkably, when analyzing the EBV-specific memory B-cell reservoir in vitro a diminished or absent number of EBNA-1- and VCA-antibody secreting cells was found in up to 76% of patients. Moreover, the ex vivo EBV-induced secretion of TNF-α and IFN-γ was significantly lower in patients. Multicolor flow cytometry revealed that the frequencies of EBNA-1-specific triple TNF-α/IFN-γ/IL-2 producing CD4(+) and CD8(+) T-cell subsets were significantly diminished whereas no difference could be detected for HCMV-specific T-cell responses. When comparing EBV load in blood immune cells, we found more frequently EBER-DNA but not BZLF-1 RNA in CFS patients compared to healthy controls suggesting more frequent latent replication. Taken together, our findings give evidence for a deficient EBV-specific B- and T-cell memory response in CFS patients and suggest an impaired ability to control early steps of EBV reactivation. In addition the diminished EBV response might be suitable to develop diagnostic marker in CFS.

EBV infection is common in gingival epithelial cells of the periodontium and worsens during chronic periodontitis

An amplifying role for oral epithelial cells (ECs) in Epstein-Barr Virus (EBV) infection has been postulated to explain oral viral shedding. However, while lytic or latent EBV infections of oro/nasopharyngeal ECs are commonly detected under pathological conditions, detection of EBV-infected ECs in healthy conditions is very rare. In this study, a simple non-surgical tissue sampling procedure was used to investigate EBV infection in the periodontal epithelium that surrounds and attaches teeth to the gingiva. Surprisingly, we observed that the gingival ECs of the periodontium (pECs) are commonly infected with EBV and may serve as an important oral reservoir of latently EBV-infected cells. We also found that the basal level of epithelial EBV-infection is significantly increased in chronic periodontitis, a common inflammatory disease that undermines the integrity of tooth-supporting tissues. Moreover, the level of EBV infection was found to correlate with disease severity. In inflamed tissues, EBV-infected pECs appear to be prone to apoptosis and to produce larger amounts of CCL20, a pivotal inflammatory chemokine that controls tissue infiltration by immune cells. Our discovery that the periodontal epithelium is a major site of latent EBV infection sheds a new light on EBV persistence in healthy carriers and on the role of this ubiquitous virus in periodontitis. Moreover, the identification of this easily accessible site of latent infection may encourage new approaches to investigate and monitor other EBV-associated disorders.

BamHI-A rightward frame 1, an Epstein-Barr virus-encoded oncogene and immune modulator

Epstein–Barr virus (EBV) causes several benign and malignant disorders of lymphoid and epithelial origin. EBV-related tumors display distinct patterns of viral latent gene expression, of which the BamHI-A rightward frame 1 (BARF1) is selectively expressed in carcinomas, regulated by cellular differentiation factors including ΔNp63α. BARF1 functions as a viral oncogene, immortalizing and transforming epithelial cells of different origin by acting as a mitogenic growth factor, inducing cyclin-D expression, and up-regulating antiapoptotic Bcl-2, stimulating host cell growth and survival. In addition, secreted hexameric BARF1 has immune evasive properties, functionally corrupting macrophage colony stimulating factor, as supported by recent functional and structural data. Therefore, BARF1, an intracellular and secreted protein, not only has multiple pathogenic functions but also can function as a target for immune responses. Deciphering the role of BARF1 in EBV biology will contribute to novel diagnostic and treatment options for EBV-driven carcinomas. Herein, we discuss recent insights on the regulation of BARF1 expression and aspects of structure-function relating to its oncogenic and immune suppressive properties. © 2013 The Authors. Reviews in Medical Virology published by John Wiley & Sons, Ltd.

NF-κB and IRF7 pathway activation by Epstein-Barr virus Latent Membrane Protein 1

The principal Epstein-Barr virus (EBV) oncoprotein, Latent Membrane Protein 1 (LMP1), is expressed in most EBV-associated human malignancies. LMP1 mimics CD40 receptor signaling to provide infected cells with constitutive NF-κB, MAP kinase, IRF7, and PI3 kinase pathway stimulation. EBV-transformed B-cells are particularly dependent on constitutive NF-κB activity, and rapidly undergo apoptosis upon NF-κB blockade. Here, we review LMP1 function, with special attention to current understanding of the molecular mechanisms of LMP1-mediated NF-κB and IRF7 pathway activation. Recent advances include the elucidation of transmembrane motifs important for LMP1 trafficking and ligand-independent signaling, analysis of genome-wide LMP1 gene targets, and the identification of novel cell proteins that mediate LMP1 NF-κB and IRF7 pathway activation.

Epstein-Barr virus transcytosis through polarized oral epithelial cells

Although Epstein-Barr virus (EBV) is an orally transmitted virus, viral transmission through the oropharyngeal mucosal epithelium is not well understood. In this study, we investigated how EBV traverses polarized human oral epithelial cells without causing productive infection. We found that EBV may be transcytosed through oral epithelial cells bidirectionally, from both the apical to the basolateral membranes and the basolateral to the apical membranes. Apical to basolateral EBV transcytosis was substantially reduced by amiloride, an inhibitor of macropinocytosis. Electron microscopy showed that virions were surrounded by apical surface protrusions and that virus was present in subapical vesicles. Inactivation of signaling molecules critical for macropinocytosis, including phosphatidylinositol 3-kinases, myosin light-chain kinase, Ras-related C3 botulinum toxin substrate 1, p21-activated kinase 1, ADP-ribosylation factor 6, and cell division control protein 42 homolog, led to significant reduction in EBV apical to basolateral transcytosis. In contrast, basolateral to apical EBV transcytosis was substantially reduced by nystatin, an inhibitor of caveolin-mediated virus entry. Caveolae were detected in the basolateral membranes of polarized human oral epithelial cells, and virions were detected in caveosome-like endosomes. Methyl β-cyclodextrin, an inhibitor of caveola formation, reduced EBV basolateral entry. EBV virions transcytosed in either direction were able to infect B lymphocytes. Together, these data show that EBV transmigrates across oral epithelial cells by (i) apical to basolateral transcytosis, potentially contributing to initial EBV penetration that leads to systemic infection, and (ii) basolateral to apical transcytosis, which may enable EBV secretion into saliva in EBV-infected individuals.

Sjögren's syndrome (SS) and Epstein-Barr virus (EBV) reactivation

Recent reports have shown that dry eye in Sjögren's syndrome (SS) is associated with reactivation of Epstein-Barr virus (EBV) in lacrimal glands. However, the number of patients examined were few and it has not been determined whether dry eye in the absence of SS is also related to EBV reactivation. The authors examined the serum antibody titers to EBV in three groups of patients: (1) simple dry eye (SDE)-dry eye with no circulating autoantibodies (n = 157), (2) autoimmune positive dry eye (ADE)-dry eye with circulating autoantibodies (n = 68), and (3) Sjögren's syndrome (SS)-dry eye associated with Sjögren's syndrome (n = 62). Healthy volunteers were recruited as controls (n = 47). In SS, the mean antibody titers to EBV nuclear antigen (anti-EBNA), early antigen (anti-EA-IgG), and virus capsid antigen (anti-VCA-IgG) were significantly elevated compared to those of controls. No significant differences in antibody titers were found among ADE, SDE, and the controls. The EBV reactivated pattern was found in 17.7% of SS, which was significantly higher than the 4.4% in ADE, 1.9% in SDE, 0% in controls. These findings suggest an association of EBV with SS, but not ADE or SDE.

Epstein-Barr virus transcription activator R upregulates BARF1 expression by direct binding to its promoter, independent of methylation

Epstein-Barr virus (EBV) BamHI-A rightward frame 1 (BARF1) is considered a major viral oncogene in epithelial cells and has immune-modulating properties. However, in B cells and lymphomas, BARF1 expression is restricted to the viral lytic replication cycle. In this report, the transcriptional regulation of BARF1 during lytic replication is unraveled. Bisulfite sequencing of various cell lines indicated a high level of methylation of the BARF1 gene control region. A BARF1 promoter luciferase reporter construct was created using a CpG-free vector, enabling true assessment of promoter methylation. Induction of the EBV lytic cycle is mediated by the immediate-early proteins BZLF1 (Z) and BRLF1 (R). R was found to activate expression of the BARF1 promoter up to 250-fold independently of Z and unaffected by BARF1 promoter methylation. Chromatin immunoprecipitation (ChIP), electrophoretic mobility shift assay (EMSA), and specific mutagenesis of the R-responsive elements (RREs) demonstrated direct binding of R to RREs between nucleotides -554 and -327 relative to the BARF1 transcriptional ATG start site. The kinetics of BARF1 expression upon transactivation by R showed that BARF1 mRNA was expressed within 6 h in the context of the viral genome. In conclusion, expression of the BARF1 protein during lytic replication is regulated by direct binding of R to multiple RREs in the gene control region and is independent of the promoter methylation status. The early kinetics of BARF1 upon transactivation by R confirm its status as an early gene and emphasize the necessity of early immune modulation during lytic reactivation.

The biology of EBV infection in human epithelial cells

EBV-associated human malignancies may originate from B cells and epithelial cells. EBV readily infects B cells in vitro and transforms them into proliferative lymphoblastoid cell lines. In contrast, infection of human epithelial cells in vitro with EBV has been difficult to achieve. The lack of experimental human epithelial cell systems for EBV infection has hampered the understanding of biology of EBV infection in epithelial cells. The recent success to infect human epithelial cells with EBV in vitro has allowed systematic investigations into routes of EBV entry, regulation of latent and lytic EBV infection, and persistence of EBV infection in infected epithelial cells. Understanding the biology of EBV infection in human epithelial cells will provide important insights to the role of EBV infection in the pathogenesis of EBV-associated epithelial malignancies including nasopharyngeal carcinoma and gastric carcinoma.

Aryl hydrocarbon receptor-mediated induction of EBV reactivation as a risk factor for Sjögren's syndrome

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates a variety of biological effects by binding to environmental pollutants, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or dioxin). Although numerous animal studies have demonstrated the harmful effects of dioxins, it remains controversial whether dioxins pose a risk to human health. Enhanced lytic replication of EBV is a risk factor for the development of autoimmune diseases and cancers. This study evaluated the possibility that ligand-activated AhR reactivates EBV. EBV reactivation and AhR transactivation were evaluated with luciferase assays. Saliva samples were collected from 19 patients with primary Sjögren's syndrome (SS). Control saliva samples were obtained from 10 healthy individuals and nine patients with severe dry mouth. TCDD enhanced BZLF1 transcription, which mediates the switch from the latent to the lytic form of EBV infection in EBV-positive B cell lines and in a salivary gland epithelial cell line. Moreover, TCDD-induced increases in BZLF1 mRNA and EBV genomic DNA levels were confirmed in the B cell lines. Saliva from SS patients activated the transcription of both CYP1A1 and BZLF1. Additionally, there was a positive correlation between CYP1A1 and BZLF1 promoter activities. AhR ligands elicited the reactivation of EBV in activated B cells and salivary epithelial cells, and these ligands are involved in SS. Our findings reveal novel aspects of the biological effects of dioxin and the AhR-dependent pathogenesis of autoimmune diseases.

Natural and adoptive T-cell immunity against herpes family viruses after allogeneic hematopoietic stem cell transplantation

Reactivated infections with herpes family-related cytomegalovirus, Epstein-Barr virus and varicella zoster virus are serious and sometimes life-threatening complications for patients undergoing allogeneic hematopoietic stem cell transplantation. The pathogenesis of these infections critically involves the slow and inefficient recovery of antiviral T-cell immunity after transplantation. Although efficient drugs to decrease viral load during this vulnerable period have been developed, long-term control of herpes viruses and protection from associated diseases require the sufficient reconstitution of virus-specific memory T cells. To heal the deficiency by immunotherapeutic means, numerous research groups have developed antiviral vaccines and strategies based on the adoptive transfer of virus-specific T cells. This article summarizes the substantial progress made in this field during the past two decades and gives future perspectives about challenges that need to be addressed before antigen-specific immunotherapy against herpes family viruses can be implemented in general clinical practice.

Exploiting the interplay between innate and adaptive immunity to improve immunotherapeutic strategies for Epstein-Barr-virus-driven disorders

The recent demonstration that immunotherapeutic approaches may be clinically effective for cancer patients has renewed the interest for this strategy of intervention. In particular, clinical trials using adoptive T-cell therapies disclosed encouraging results, particularly in the context of Epstein-Barr-virus- (EBV-) related tumors. Nevertheless, the rate of complete clinical responses is still limited, thus stimulating the development of more effective therapeutic protocols. Considering the relevance of innate immunity in controlling both infections and cancers, innovative immunotherapeutic approaches should take into account also this compartment to improve clinical efficacy. Evidence accumulated so far indicates that innate immunity effectors, particularly NK cells, can be exploited with therapeutic purposes and new targets have been recently identified. We herein review the complex interactions between EBV and innate immunity and summarize the therapeutic strategies involving both adaptive and innate immune system, in the light of a fruitful integration between these immunotherapeutic modalities for a better control of EBV-driven tumors.

Epstein-Barr virus (EBV) Rta-mediated EBV and Kaposi's sarcoma-associated herpesvirus lytic reactivations in 293 cells

Epstein–Barr virus (EBV) Rta belongs to a lytic switch gene family that is evolutionarily conserved in all gamma-herpesviruses. Emerging evidence indicates that cell cycle arrest is a common means by which herpesviral immediate-early protein hijacks the host cell to advance the virus's lytic cycle progression. To examine the role of Rta in cell cycle regulation, we recently established a doxycycline (Dox)-inducible Rta system in 293 cells. In this cell background, inducible Rta modulated the levels of signature G1 arrest proteins, followed by induction of the cellular senescence marker, SA-β-Gal. To delineate the relationship between Rta-induced cell growth arrest and EBV reactivation, recombinant viral genomes were transferred into Rta-inducible 293 cells. Somewhat unexpectedly, we found that Dox-inducible Rta reactivated both EBV and Kaposi's sarcoma-associated herpesvirus (KSHV), to similar efficacy. As a consequence, the Rta-mediated EBV and KSHV lytic replication systems, designated as EREV8 and ERKV, respectively, were homogenous, robust, and concurrent with cell death likely due to permissive lytic replication. In addition, the expression kinetics of EBV lytic genes in Dox-treated EREV8 cells was similar to that of their KSHV counterparts in Dox-induced ERKV cells, suggesting that a common pathway is used to disrupt viral latency in both cell systems. When the time course was compared, cell cycle arrest was achieved between 6 and 48 h, EBV or KSHV reactivation was initiated abruptly at 48 h, and the cellular senescence marker was not detected until 120 h after Dox treatment. These results lead us to hypothesize that in 293 cells, Rta-induced G1 cell cycle arrest could provide (1) an ideal environment for virus reactivation if EBV or KSHV coexists and (2) a preparatory milieu for cell senescence if no viral genome is available. The latter is hypothetical in a transient-lytic situation.

Epstein-Barr virus-associated primary central nervous system lymphoma in a patient with adult T-cell leukemia / lymphoma

We present a case of Epstein-Barr virus (EBV)-associated primary central nervous system lymphoma (PCNSL) arising from a patient with cutaneous-type adult T-cell leukemia/lymphoma (ATLL). Extranodal sites affected by ATLL include the skin, lung, liver, gastrointestinal tract and central nervous system (CNS). CNS involvement usually occurs as an acute and lymphoma-type ATLL. PCNSL is a rare type of tumor and the vast majority of PCNSL are of B-cell lineage. Individuals with acquired, iatrogenic or congenital immunodeficiency are at increased risk of PCNSL, which is commonly associated with EBV. In our patient, the expression of latent infection membrane protein 1 (LMP1), EBV nuclear antigen 2 (EBNA2), and EBV-encoded small RNA (EBER) in tumor cells confirmed a type III latency of EBV infection. Human T-cell lymphotropic virus type I (HTLV-I) can induce immunodeficiency before the overt development of ATLL. The HTLV-I infection led to suppression of the immune system and the development of EBV-associated PCNSL. This is the first reported case of the clinicopathological features of EBV-associated PCNSL arising from a patient with ATLL.

Serological detection of Epstein-Barr virus infection in dogs and cats

Epstein-Barr virus (EBV) is widespread in humans world-wide. The virus, which is linked to Burkitt's and Hodgkin lymphoma in humans, has recently been detected in pet dogs in Taiwan. The aim of this study was to determine if EBV is present in other canine populations, whether infection is associated with lymphoma in dogs, and whether infection is present in cats. Canine and feline serum samples were analysed by immunofluorescence assay. Antibodies to EBV or an EBV-like virus were detected in 38.4% of UK dog sera, 64% of US dog sera and 38% of cat sera. Canine blood samples, tissue samples from the palatine tonsil and formalin-fixed, paraffin-embedded biopsy samples from canine lymphoma cases were analysed by PCR. Using EBV-specific primers, EBV was detected in one tonsil sample, whereas all other samples tested were negative. PCR using consensus herpesvirus primers identified canine herpesvirus in twelve tonsil samples and one biopsy but no gammaherpesviruses were detected. Canine blood samples from EBV antibody-positive dogs were analysed by RT-PCR to determine if transcripts associated with lytic EBV infection (BcLF1) or latency (LMP2) were present, however all samples tested were negative. In conclusion, there is serological evidence of exposure to EBV or an EBV-like virus in dogs and cats but persistent infection in the canine palatine tonsil is rare and no evidence was found of EBV in canine peripheral blood mononuclear cells. The effect of EBV on canine and feline cells and the possible outcome of the infection for the host require further investigation.

EBV Chronic Infections

The infection from Epstein-Barr virus (EBV) or virus of infectious mononucleosis, together with other herpes viruses' infections, represents a prototype of persistent viral infections characterized by the property of the latency. Although the reactivations of the latent infection are associated with the resumption of the viral replication and eventually with the "shedding", it is still not clear if this virus can determine chronic infectious diseases, more or less evolutive. These diseases could include some pathological conditions actually defined as "idiopathic"and characterized by the "viral persistence" as the more credible pathogenetic factor. Among the so-called idiopathic syndromes, the "chronic fatigue syndrome" (CFS) aroused a great interest around the eighties of the last century when, just for its relationship with EBV, it was called "chronic mononucleosis" or "chronic EBV infection".Today CFS, as defined in 1994 by the CDC of Atlanta (USA), really represents a multifactorial syndrome characterized by a chronic course, where reactivation and remission phases alternate, and by a good prognosis. The etiopathogenetic role of EBV is demonstrated only in a well-examined subgroup of patients, while in most of the remaining cases this role should be played by other infectious agents - able to remain in a latent or persistent way in the host - or even by not infectious agents (toxic, neuroendocrine, methabolic, etc.). However, the pathogenetic substrate of the different etiologic forms seems to be the same, much probably represented by the oxidative damage due to the release of pro-inflammatory cytokines as a response to the triggering event (infectious or not infectious).Anyway, recently the scientists turned their's attention to the genetic predisposition of the subjects affected by the syndrome, so that in the last years the genetic studies, together with those of molecular biology, received a great impulse. Thanks to both these studies it was possibile to confirm the etiologic links between the syndrome and EBV or other herpesviruses or other persistent infectious agents.The mechanisms of EBV latency have been carefully examined both because they represent the virus strategy to elude the response of the immune system of the host, and because they are correlated with those oncologic conditions associated to the viral persistence, particularly lymphomas and lymphoproliferative disorders. Just these malignancies, for which a pathogenetic role of EBV is clearly documented, should represent the main clinical expression of a first group of chronic EBV infections characterized by a natural history where the neoplastic event aroused from the viral persistence in the resting B cells for all the life, from the genetic predisposition of the host and from the oncogenic potentialities of the virus that chronically persists and incurs reactivations.Really, these oncological diseases should be considered more complications than chronic forms of the illness, as well as other malignancies for which a viral - or even infectious - etiology is well recognized. The chronic diseases, in fact, should be linked in a pathogenetic and temporal way to the acute infection, from whom start the natural history of the following disease. So, as for the chronic liver diseases from HBV and HCV, it was conied the acronym of CAEBV (Chronic Active EBV infection), distinguishing within these pathologies the more severe forms (SCAEBV) mostly reported in Far East and among children or adolescents. Probably only these forms have to be considered expressions of a chronic EBV infection "sensu scrictu", together with those forms of CFS where the etiopathogenetic and temporal link with the acute EBV infection is well documented. As for CFS, also for CAEBV the criteria for a case definition were defined, even on the basis of serological and virological findings. However, the lymphoproliferative disorders are excluded from these forms and mantain their nosographic (e.g. T or B cell or NK type lymphomas) and pathogenetic collocation, even when they occur within chronic forms of EBV infection. In the pathogenesis, near to the programs of latency of the virus, the genetic and environmental factors, independent from the real natural history of EBV infection, play a crucial role.Finally, it was realized a review of cases - not much numerous in literature - of chronic EBV infection associated to chronic liver and neurological diseases, where the modern techniques of molecular biology should be useful to obtain a more exact etiologic definition, not always possibile to reach in the past.The wide variety of clinical forms associated to the EBV chronic infection makes difficult the finding of a univocal pathogenetic link. There is no doubt, however, that a careful examination of the different clinical forms described in this review should be useful to open new horizons to the study of the persistent viral infections and the still not well cleared pathologies that they can induce in the human host.

Epstein-Barr virus can infect rabbits by the intranasal or peroral route: an animal model for natural primary EBV infection in humans

Epstein-Barr virus (EBV) is spread universally in humans, and it causes infectious mononucleosis and sometimes induces serious EBV-associated disease. The detailed mechanism of primary infection in humans has remained unclear, because it is difficult to examine the dynamics of EBV in vivo. In this study, a natural EBV-infection rabbit model by intranasal or peroral inoculation is described. Ten male rabbits were examined for EBV-DNA or mRNA expression and anti-EBV antibodies in blood. Four of 10 rabbits showed the evidence of EBV infection; detection of EBV-DNA or EBV-related genes mRNA in peripheral blood mononuclear cells, increased EBV antibodies in the plasma, and the presence of lymphocytes expressing EBER1 and EBV-related gene proteins in the lymphoid tissues of a rabbit. Three of four infected rabbits were detected transiently EBV-DNA and/or mRNA of EBV-related genes such as EBNA1, EBNA2, BZLF1, and EA in blood, while in one of four, EBV-DNA and/or mRNA were detected for more than 200 days after viral inoculation. The level of EA-IgG increased and its level was maintained in all infected rabbits, whereas those of VCA-IgM and VCA-IgG increased transiently, and EBNA-IgG was not elevated. Pathological examination of a rabbit infected transiently revealed some scattered lymphocytes expressing EBER1, LMP1, and EBNA2 in the spleen and lymph nodes. EA expression was also observed in the spleen. These findings suggest that EBV can infect the rabbit by the intranasal or peroral route, and that this rabbit model is useful for examining the pathophysiology of natural primary EBV infection in humans.

Endemic Burkitt's lymphoma as a polymicrobial disease: new insights on the interaction between Plasmodium falciparum and Epstein-Barr virus

Despite the well-established relationship between endemic Plasmodium falciparum malaria and Epstein-Barr virus (EBV) infection in the genesis of endemic Burkitt's lymphoma (eBL), very little research has examined the interaction between these two pathogens. eBL, the most prevalent childhood cancer in equatorial Africa where malaria is holoendemic, is a high-grade B cell lymphoma characterized by a c-myc translocation and the consistent presence of EBV. After primary infection, EBV establishes a life-long persistent infection characterized by virus shedding into saliva. African children are infected early in life and most have sero-converted by 3 years of age while sero-conversion tends to occur later in developed countries. Acute and chronic malaria infections profoundly affect the B cell compartment, inducing polyclonal activation, hyper-gammaglobulinemia and a dramatic increase in the levels of circulating EBV. In this review we present and discuss recent data suggesting a molecular link between the parasite, the B cell and EBV and provide evidence that adds to the concept of polymicrobial disease pathogenesis in eBL. Following the observation of EBV reactivation in children living in malaria endemic areas and its relationship with acute malaria infection, we identified the cystein-rich inter-domain region 1 alpha (CIDR1 alpha) of the Plasmodium falciparum membrane protein 1 as a polyclonal B cell activator. CIDR1 alpha increases B cell survival and preferentially activates the memory compartment where EBV is known to persist. Analysis of the mechanisms of interaction between CIDR1 alpha and EBV in the context of B cells demonstrated that CIDR1 alpha induces virus production in the EBV-infected B cell line Akata and in latently infected primary B cells derived from the peripheral blood of healthy carriers and children with eBL. This is the first demonstration that EBV can be reactivated directly by another pathogen. Our results suggest that P. falciparum antigens such as PfEMP1 can directly induce EBV reactivation during malaria infections. The increased viral load and the concomitant polyclonal B cell activation with enhanced B cell survival may augment the risk of eBL development in children living in malaria-endemic areas.

Valacyclovir pharmacokinetics and exploratory pharmacodynamics in young adults with Epstein-Barr virus infectious mononucleosis

Primary Epstein-Barr virus (EBV) infection often results in infectious mononucleosis and is associated with serious sequelae. No treatment is approved for EBV infection, and an antiviral intervention would be significant. The objectives of this study are to characterize the pharmacokinetics and explore the pharmacodynamics of acyclovir in plasma and oral washings of 8 subjects receiving 7 days of valacyclovir 1500 mg twice daily for EBV infectious mononucleosis. Virologic and clinical responses are assessed over 12 days. Acyclovir is measured by liquid chromatography/ultraviolet detection. EBV DNA is quantitated by TaqMan polymerase chain reaction. NONMEM VI and linear regression are used for data analysis. Acyclovir profiles in plasma and oral washings are consistent with a 1-compartment model. Final model estimates of clearance, volume of distribution, and fraction of acyclovir in oral wash supernatant are 49.9 L/h, 74.1 L, and 1.14%, respectively. The quantity of EBV DNA in oral washings and blood, and the severity of illness, measured by a graded scale, decrease during treatment. After treatment, viral rebound occurs in oral washings but not in blood, and the severity of illness continues to decline. Acyclovir pharmacokinetic parameters do not correlate with response metrics. These results support further studies of valacyclovir for EBV infectious mononucleosis.

Features distinguishing Epstein-Barr virus infections of epithelial cells and B cells: viral genome expression, genome maintenance, and genome amplification

Epstein-Barr virus (EBV) is associated with malignant diseases of lymphoid and epithelial cell origin. The tropism of EBV is due to B-cell-restricted expression of CD21, the major receptor molecule for the virus. However, efficient infection of CD21- epithelial cells can be achieved via transfer from EBV-coated B cells. We compare and contrast here the early events following in vitro infection of primary B cells and epithelial cells. Using sensitive, quantitative reverse transcription-PCR assays for several latent and lytic transcripts and two-color immunofluorescence staining to analyze expression at the single cell level, we confirmed and extended previous reports indicating that the two cell types support different patterns of transcription. Furthermore, whereas infection of B cells with one or two copies of EBV resulted in rapid amplification of the viral genome to >20 copies per cell, such amplification was not normally observed after infection of primary epithelial cells or undifferentiated epithelial lines. In epithelial cells, EBNA1 expression was detected in only ca. 40% of EBER+ cells, and the EBV genome was subsequently lost during prolonged culture. One exception was that infection of AGS, a gastric carcinoma line, resulted in maintenance of EBNA1 expression and amplification of the EBV episome. In contrast to B cells, where amplification of the EBV episome occurred even with a replication-defective BZLF1-knockout virus, amplification in AGS cells was dependent upon early lytic cycle gene expression. These data highlight the influence of the host cell on the outcome of EBV infection with regard to genome expression, amplification, and maintenance.

EBV BMRF-2 facilitates cell-to-cell spread of virus within polarized oral epithelial cells

We previously reported that the Epstein-Barr virus (EBV) BMRF-2 protein plays an important role in EBV infection of polarized oral epithelial cells by interacting with beta1 and alphav family integrins. Here we show that infection of polarized oral epithelial cells with B27-BMRF-2(low) recombinant virus, expressing a low level of BMRF-2, resulted in significantly smaller plaques compared with infection by parental B95-8 virus. BMRF-2 localized in the trans-Golgi network (TGN) and basolateral sorting vesicles and was transported to the basolateral membranes of polarized epithelial cells. Mutation of the tyrosine- and dileucine-containing basolateral sorting signal, YLLV, in the cytoplasmic domain of BMRF-2 led to the failure of its accumulation in the TGN and its basolateral transport. These data show that BMRF-2 may play an important role in promoting the spread of EBV progeny virions through lateral membranes of oral epithelial cells.

Recurrent chemical reactivations of EBV promotes genome instability and enhances tumor progression of nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma (NPC) is an endemic malignancy prevalent in South East Asia. Epidemiological studies have associated this disease closely with Epstein-Barr virus (EBV) infection. Previous studies also showed that EBV reactivation is implicated in the progression of NPC. Thus, we proposed that recurrent reactivations of EBV may be important for its pathogenic role. In this study, NPC cell lines latently infected with EBV, NA and HA, and the corresponding EBV-negative NPC cell lines, NPC-TW01 (TW01) and HONE-1, were treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) and sodium n-butyrate (SB) for lytic cycle induction. A single treatment with TPA/SB revealed that DNA double-strand breaks and formation of micronuclei (a marker for genome instability) were associated with EBV reactivation in NA and HA cells. Examination of EBV early genes had identified several lytic proteins, particularly EBV DNase, as potent activators that induced DNA double-strand breaks and contribute to genome instability. Recurrent reactivations of EBV in NA and HA cells resulted in a marked increase of genome instability. In addition, the degree of chromosomal aberrations, as shown by chromosome structural variants and DNA copy-number alterations, is proportional to the frequency of TPA/SB-induced EBV reactivation. Whereas these DNA abnormalities were limited in EBV-negative TW01 cells with mock or TPA/SB treatment, and were few in mock-treated NA cells. The invasiveness and tumorigenesis assays also revealed a profound increase in both characteristics of the repeatedly reactivated NA cells. These results suggest that recurrent EBV reactivations may result in accumulation of genome instability and promote the tumor progression of NPC.

Independent effect of EBV and cigarette smoking on nasopharyngeal carcinoma: a 20-year follow-up study on 9,622 males without family history in Taiwan

This study aimed to assess independent effects of EBV and cigarette smoking on nasopharyngeal carcinoma, which have never been assessed in long-term follow-up studies. A cohort of 9,622 men was enrolled from 1984 to 1986. Blood samples collected at study entry were tested for antibodies against EBV antigens (anti-EBV) viral capsid antigen immunoglobulin A and DNase. The cigarette smoking habit was inquired through questionnaire interview. Newly developed nasopharyngeal carcinoma cases were ascertained through computerized linkage with national cancer registry profile. Cox's proportional hazard regression analysis was used to estimate multivariate-adjusted hazard ratio with its 95% confidence interval (95% CI). During the follow-up of 173,706 person-years, 32 pathologically confirmed nasopharyngeal carcinoma cases were identified >1 year after recruitment. Increasing serum levels of anti-EBV viral capsid antigen immunoglobulin A and DNase were significantly associated with nasopharyngeal carcinoma risk in a dose-response relationship. The multivariate-adjusted hazard ratio (95% CI) of developing nasopharyngeal carcinoma for low and high antibody levels compared with seronegatives was 9.5 (2.2-40.1) and 21.4 (2.8-161.7), respectively, for anti-EBV viral capsid antigen immunoglobulin A (P < 0.001 for trend), and 1.6 (0.5-4.6) and 16.0 (5.4-47.1), respectively, for anti-EBV DNase (P < 0.001 for trend). The shorter the time interval between study entry and nasopharyngeal carcinoma diagnosis, the higher was the proportion of anti-EBV viral capsid antigen immunoglobulin A among nasopharyngeal carcinoma patients. The multivariate-adjusted hazard ratio (95% CI) was 3.0 (1.3-7.2) for > or =30 pack-years of cumulative cigarette smoking compared with <30 pack-years as the reference. The longer and heavier the cigarette smoking habit, the higher was the nasopharyngeal carcinoma risk. Anti-EBV viral capsid antigen immunoglobulin A, anti-EBV DNase, and long-term heavy cigarette smoking are independent nasopharyngeal carcinoma risk predictors.

Methylation-dependent binding of the epstein-barr virus BZLF1 protein to viral promoters

The switch between latent and lytic Epstein-Barr virus (EBV) infection is mediated by the viral immediate-early (IE) protein, BZLF1 (Z). Z, a homologue of c-jun that binds to AP1-like motifs (ZREs), induces expression of the BRLF1 (R) and BRRF1 (Na) viral proteins, which cooperatively activate transcription of the Z promoter and thereby establish a positive autoregulatory loop. A unique feature of Z is its ability to preferentially bind to, and activate, the methylated form of the BRLF1 promoter (Rp). To date, however, Rp is the only EBV promoter known to be regulated in this unusual manner. We now demonstrate that the promoter driving transcription of the early BRRF1 gene (Nap) has two CpG-containing ZREs (ACGCTCA and TCGCCCG) that are only bound by Z in the methylated state. Both Nap ZREs are highly methylated in cells with latent EBV infection. Z efficiently activates the methylated, but not unmethylated, form of Nap in reporter gene assays, and both ZREs are required. Z serine residue 186, which was previously shown to be required for Z binding to methylated ZREs in Rp, but not for Z binding to the AP1 site, is required for Z binding to methylated Nap ZREs. The Z(S186A) mutant cannot activate methylated Nap in reporter gene assays and does not induce Na expression in cells with latent EBV infection. Molecular modeling studies of Z bound to the methylated Nap ZREs help to explain why methylation is required for Z binding, and the role of the Z Ser186 residue. Methylation-dependent Z binding to critical viral promoters may enhance lytic reactivation in latently infected cells, where the viral genome is heavily methylated. Conversely, since the incoming viral genome is initially unmethylated, methylation-dependent Z activation may also help the virus to establish latency following infection.

In cells with long-term latent Epstein-Barr virus (EBV) infection, the majority of the EBV genome becomes highly methylated. Methylation of cytosines plays a critical role in inhibiting the expression of cellular genes. In contrast, our laboratory previously showed that the EBV protein, BZLF1 (Z), which mediates viral reactivation and replication, preferentially binds to, and activates, the methylated form of the viral BRLF1 promoter. To date, however, BRLF1 is the only EBV promoter known to be activated by Z in this unusual manner. Here, we show that another EBV promoter (Nap, driving transcription of the BRRF1 gene) likewise has two methylation-dependent Z binding sites, and that Z only activates the Nap efficiently in the methylated form. Molecular modeling studies suggest why methylation of the Nap enhances Z binding. Since the BRLF1 and BRRF1 genes encode essential viral transcription factors that work cooperatively with Z to induce the lytic form of viral infection, our results indicate that methylation of the EBV genome enhances Z-mediated disruption of viral latency.

Induction of Epstein-Barr virus (EBV) lytic cycle in vitro causes oxidative stress in lymphoblastoid B cell lines

Here, we investigated the effect of induction of the Epstein-Barr virus (EBV) viral lytic cycle on the oxidant/antioxidant balance in three lymphoblastoid cell lines: B95-8, Raji, and LCL C1. The induction of the EBV lytic cycle was done by a non-stressing dose of 12-0-tetradecanoylphorbol-13-acetate (8 nM). Oxidative stress was assessed by measuring malondialdehyde as a parameter of lipid peroxidation, the levels of glutathione, and the activities of three antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase). After 48 h (peak of lytic cycle), a significant decrease in superoxide dismutase activity was observed in B95-8, Raji, and LCL C1 cells (P < 0.05). In addition, in B95-8 cells also a significant decrease of catalase activity was detected (P < 0.05). The glutathione peroxidase activity and the glutathione level were not significantly modified by the induction in any of the cell lines. We found a significant rise in malondialdehyde levels in B95-8, Raji, and LCL C1 cells after the induction of the lytic cycle compared to controls (P < 0.05). In conclusion, induction of EBV lytic cycle in lymphoblastoid cells causes increased oxidative stress in the host cells within 48 h, a process that could be involved in malignant transformations.

Oral Hairy Leukoplakia in HIV-Negative Patients: Report of 10 Cases

Ten cases of oral hairy leukoplakia (OHL) in HIV- negative patients are presented. Eight of the 10 patients were on steroid treatment for chronic obstructive pulmonary disease, 1 patient was on prednisone as part of a therapeutic regimen for gastrointestinal stromal tumor, and 1 patient did not have any history of immunosuppression. There were 5 men and 5 women, ages 32-79, with mean age being 61.8 years. Nine out of 10 lesions were located unilaterally on the tongue, whereas 1 lesion was located at the junction of the hard and soft palate. All lesions were described as painless, corrugated, nonremovable white plaques (leukoplakias). Histologic features were consistent with Epstein—Barr virus—associated hyperkeratosis suggestive of OHL, and confirmatory in situ hybridization was performed in all cases. Candida hyphae and spores were present in 8 cases. Pathologists should be aware of OHL presenting not only in HIV-positive and HIV-negative organ transplant recipients but also in patients receiving steroid treatment, and more important, certain histologic features should raise suspicion for such diagnosis without prior knowledge of immunosuppression.

Oropharyngeal shedding of Epstein-Barr virus in the absence of circulating B cells

Infection with Epstein-Barr virus (EBV) results in lifelong infection of B cells in the peripheral blood and in episodic shedding of virus from the oropharynx. We monitored patients treated with rituximab (anti-CD20 monoclonal antibody) and found that several had both no detectable B cells and no EBV in the blood but shed EBV from the throat. Although some models postulate that EBV traffics from the B cells in the blood to the throat, where it is subsequently shed, our findings indicate that circulating EBV in B cells is not necessary for the virus to persist in, and to be shed from, the oropharynx.

Human cytomegalovirus and Epstein-Barr virus in apical and marginal periodontitis: a role in pathology?

Periodontitis is presumably caused by bacterial infection, but it has been shown recently that affected tissue often contains human cytomegalovirus (HCMV) and Epstein-Barr virus (EBV). The present study was initiated to evaluate the role of these viruses in the pathogenesis of periodontitis. HCMV and EBV were quantified in 40 apical and 25 marginal periodontitis samples using real time PCR. In situ hybridization or immunohistochemistry was carried out on apical samples to detect viral presence within cells. A possible association with relevant bacteria was examined. Of the apical periodontitis samples, 50% contained EBV, while none contained HCMV. Of the marginal periodontitis samples, 40% were positive for EBV and 12% for HCMV. With one exception, however, the amount of virus was close to the detection limits. EBV was only detected in 1 out of 15 healthy periodontium samples. Immunohistochemistry and in situ hybridization were all negative. Significant associations were found between periodontal EBV and the presence of Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis. Although there was an obvious association of the virus with clinical samples, it seems unlikely that these viruses play a major role in the pathogenesis of periodontitis of the average patient. Their presence may reflect that the clinical samples contain more blood or saliva compared to controls, or an accumulation of lymphoid cells harboring virus in the inflamed tissue.

Epstein-Barr virus-associated epithelial and mesenchymal neoplasms

Epstein-Barr virus (EBV) is a ubiquitous human pathogen that usually maintains a harmonious relationship with its host. Rarely, this host-virus balance is perturbed, causing a diverse group of malignancies in both immunocompetent and immunosuppressed patients. In addition to its role in hematologic malignancies (Burkitt lymphoma, subsets of Hodgkin and T-cell lymphomas, posttransplant lymphomas), EBV has been implicated in both epithelial (undifferentiated nasopharyngeal carcinoma, a subset of gastric adenocarcinomas) and mesenchymal (EBV-associated smooth muscle tumor, inflammatory pseudotumor-like follicular dendritic cell tumor) neoplasms. This review will focus on EBV-associated epithelial and mesenchymal neoplasms.

Spectrum of Epstein-Barr virus-associated diseases

The association between Epstein-Barr virus (EBV) and a large number of benign and malignant diseases is unique among DNA viruses. Within infected tissues, proteins that are expressed during the normal lytic and latent viral life cycle lead to cellular alterations that contribute to these EBV-associated diseases. Although the early events of EBV infection are poorly understood, increasing knowledge of the viral processes that govern viral latency has shed light upon the potential mechanisms by which EBV infection can lead to cellular transformation. Our current understanding of the role of EBV in the development of Burkitt lymphoma, Hodgkin lymphoma, nasopharyngeal carcinoma, and other EBV-associated diseases is discussed.

Valproic acid enhances the efficacy of chemotherapy in EBV-positive tumors by increasing lytic viral gene expression

EBV infection in tumor cells is generally restricted to the latent forms of viral infection. Switching the latent form of viral infection into the lytic form may induce tumor cell death. We have previously reported that certain chemotherapy agents can increase the amount of lytic viral gene expression in EBV-positive tumor cells. In this report, we have explored the potential utility of valproic acid (VPA), an anti-seizure drug that also has strong histone deacetylase inhibitory activity, for activating lytic viral gene expression in EBV-positive tumors. Although VPA treatment alone induced only a modest increase in the level of lytic viral gene expression, it strongly enhanced the ability of chemotherapeutic agents to induce lytic EBV gene expression in EBV-positive epithelial and lymphoid cells in vitro. Furthermore, VPA enhanced cell killing in vitro by chemotherapeutic agents in lymphoblastoid cells and gastric cells (AGS) containing wild-type EBV. In contrast, VPA did not enhance the cytotoxicity of chemotherapy in lymphoblastoid cells containing a lytic-defective (BZLF1-knockout) form of EBV or in EBV-negative AGS cells. Finally, we found that the combination of VPA and chemotherapy was significantly more effective in inhibiting EBV-driven lymphoproliferative disease in severe combined immunodeficient mice than chemotherapy alone. These results suggest that VPA could potentiate the efficacy of chemotherapy for EBV-positive tumors in patients.

Evasion of host immune responses by tumours and viruses

Viruses and tumours use various mechanisms to avoid immune surveillance. Oncogenic viruses have achieved a balance with the immune system through evolutionary time to ensure long-term persistence. Mutations that promote escape mechanisms favouring tumour growth to the detriment of host survival through reproductive age offer no selective advantage and will not generally be maintained in the viral genome that persists in nature. Conventional (non-oncogenic) and tumour viruses interact with various immune mediators and T cells in different ways. Oncogenic viruses cannot operate solely in the context of a lytic cycle, though this may be characteristic of the initial phase of infection that is limited by the acute immune response. Some oncogenic viruses interact with normal cellular growth control and signalling mechanisms. Synthesis of key viral proteins may be tightly controlled in replicating cells that are subject to T cell surveillance, such as basal epithelia, while productive infection occurs in non-proliferating progeny that are lost under normal physiological conditions, such as desquamating epithelia. Tumorigenesis may be an aberrant consequence of the molecular mechanisms needed to maintain this pattern of viral growth regulation in the context of the cell cycle. Vaccines designed to limit the acute phase of infection with cell-free oncogenic viruses should be as effective as those for conventional viruses.

Epstein-Barr virus–associated lymphoproliferative disorders

Epstein-Barr virus (EBV) is a member of the human herpesvirus family that was initially isolated from a cultured Burkitt lymphoma cell line by Epstein et al in 1964. Subsequent studies have proven that it is the causative agent in most cases of infectious mononucleosis. Primary infection is usually asymptomatic in childhood; but in adulthood, it is associated with a self-limiting infectious mononucleosis syndrome in approximately one third of the cases. EBV has been linked to many human neoplasms including hematopoietic, epithelial, and mesenchymal tumors. In this review, we will only discuss the EBV-associated lymphoproliferative disorders, dividing them into B-cell, T/NK-cell, and HIV-related lymphoproliferative disorders.

Epstein-Barr virus B95.8 produced in 293 cells shows marked tropism for differentiated primary epithelial cells and reveals interindividual variation in susceptibility to viral infection

Epstein-Barr virus (EBV), a well-characterised B-lymphotropic agent is aetiologically linked to B cell lymphoproliferations, but the spectrum of diseases the virus causes also includes oral hairy leukoplakia, a benign epithelial lesion, as well as carcinomas of the nasopharynx and of the stomach. However, it is still unclear how EBV accesses and transforms primary epithelial cells. Sixteen samples consisting of primary epithelial cells from the sphenoidal sinus or from tonsils were infected with GFP-tagged recombinant B95.8 EBVs produced in the 293 cell line. The rate of infection was assessed by counting GFP-positive cells and cells expressing viral proteins. Primary epithelial cells from all samples were found to be sensitive to EBV infection but there was a marked interindividual variation among the tested samples (2-48% positive cells). This suggests heterogeneity in terms of sensitivity to EBV infection in vivo and therefore possibly to EBV-associated diseases of the epithelium. The virus showed a preferential tropism for differentiated epithelial cells (p63 negative, involucrin positive). In all cases, infected cells expressed EBV lytic proteins but also the LMP1 protein. The viral tropism for differentiated cells and the permissivity of these cells for virus replication reproduced in vitro cardinal features of oral hairy leukoplakia. We have identified a source of EBV that shows unusually strong epitheliotropism for primary epithelial cells that will allow detailed analysis of virus-cell interactions during virus infection, replication and virus-mediated transformation.

ZEB1 and c-Jun levels contribute to the establishment of highly lytic Epstein-Barr virus infection in gastric AGS cells

The induction of lytic infection has been proposed as a therapeutic strategy for treating Epstein-Barr virus (EBV)-positive malignancies. To succeed, efficient methods are needed for activating the EBV immediate-early (IE) promoters, Zp and Rp. Here we compared factors which regulate Zp and Rp in AGS gastric carcinoma cells that support a remarkably high level of persistently lytic EBV infection with HeLa cervical cells that permit only tightly latent infection. We found that the level of Zp activity assayed by transient transfection assays with reporter plasmids was high in AGS cells but low in HeLa cells. The level of Rp activity was low in both cell types. Mutational analysis indicated that sequences within Zp located between -70 and +27 relative to the transcription initiation site were sufficient to confer a high level of Zp activity in AGS cells. The Zp CRE motif was necessary for this constitutive activity, while the ZIA and ZIB MEF2D motifs were not. Consistent with these findings, immunoblot analysis indicated that phosphorylated c-Jun, which activates Zp through the CRE motif, was expressed at a much higher level in EBV-infected AGS cells than in EBV-infected HeLa cells. In contrast, ZEB1, which represses Zp via the ZV motif located near the transcription initiation site, was abundant in HeLa cells, while it was absent from AGS cells. Exogenous addition of ZEB1 led to the repression of Zp in AGS cells. We conclude that the unusually high Zp activity level in AGS cells is due to the high abundance of positively acting transcription factors such as c-Jun combined with the low abundance of negatively acting factors such as ZEB1.

Epstein-Barr virus BHRF1 micro- and stable RNAs during latency III and after induction of replication

Epstein-Barr virus (EBV) microRNAs miR-BHRF1-1, -2, and -3 have been detected in latency III-infected lymphoblasts, where they are encoded within EBNA transcripts (X. Cai, A. Schafer, S. Lu, J. P. Bilello, R. C. Desrosiers, R. Edwards, N. Raab-Traub, and B. R. Cullen, PLoS Pathog. 2:e23, 2006). In latency III-infected lymphoblasts, we have also identified a stable 1.3-kb RNA, which begins 3' to miR-BHRF1-1, includes the BHRF1 open reading frame, and ends near miR-BHRF1-2. This 1.3-kb RNA is the residue of Drosha cleavage of the BHRF1 microRNAs from EBNA transcripts. Early after induction of EBV replication in latency I-infected Akata lymphoblasts, BHRF1 spliced 1.4-kb mRNA accumulated along with low levels of miR-BHRF1-2 and -3 and a 0.9-kb Drosha or miR-BHRF1-2 cleavage product of BHRF1 mRNA. The turning on of latency III infection at 48 to 72 h after induction of EBV replication was associated with higher miR-BHRF1-1, -2, and -3 levels; accumulation of the 1.3-kb RNA residue in the nucleus; abundant BHRF1 spliced 1.4-kb mRNA in the cytoplasm; and more abundant 0.9-kb mRNA cleavage product in the cytoplasm. These findings implicate miR-BHRF1-2 in 3' cleavage of BHRF1 mRNA in the cytoplasm and Drosha in cleavage of latency III EBNA and EBV replication-associated BHRF1 transcripts in the nucleus.

Epstein-Barr virus lytic infection induces retinoic acid-responsive genes through induction of a retinol-metabolizing enzyme, DHRS9

Lytic Epstein-Barr virus (EBV) replication occurs in differentiated, but not undifferentiated, epithelial cells. Retinoic acid (RA) induces epithelial cell differentiation. The conversion of retinol into its active form, retinoic acid, requires retinol dehydrogenase enzymes. Here we show that AGS gastric carcinoma cells containing the lytic form of EBV infection have enhanced expression of a gene (DHRS9) encoding an enzyme that mediates conversion of retinol into RA. DHRS9 expression is also increased following induction of lytic viral infection in EBV-positive Burkitt lymphoma cells. We demonstrate that the EBV immediate-early protein, BZLF1, activates the DHRS9 promoter through a direct DNA binding mechanism. Furthermore, BZLF1 expression in AGS cells is sufficient to activate DHRS9 gene expression and increases the ability of retinol to induce the RA-responsive gene, CYP26A1. Production of RA during the lytic form of EBV infection may enhance viral replication by promoting keratinocyte differentiation.

Evidence of shared Epstein-Barr viral isolates between sexual partners, and low level EBV in genital secretions

Epstein-Barr virus is present in the saliva of most persistently infected individuals and is generally thought to be spread by close oral contact. However, there are now several reports of EBV in genital secretions, suggesting the possibility of sexual transmission between adults. The present study was undertaken to investigate the risk of sexual transmission of EBV. PCR analysis was used to examined the degree to which a group (n = 11) of patients with infectious mononucleosis (IM) shared the same viral isolates as their sexual partners, and compare this to the extent of isolate sharing among a different group (n = 18) of IM patients and their non-sexual contacts. There was significantly more sharing of EBV isolates among the IM/sexual-contact pairs than among the IM/non-sexual-contact pairs (P = 0.0012). Female cervical (n = 84), male urethral (n = 55), and semen (n = 30) samples from asymptomatic, unselected volunteers were analyzed for the presence of EBV DNA, revealing 7%, 5%, and 3% to be EBV positive, respectively. Fractionation of cervical and urethral samples into cellular and supernatant fluid components showed EBV to be mainly cell-associated. Quantitation of EBV in these samples gave levels of below 10 EBV genomes per microg of DNA. Overall the findings support the possibility that EBV could on occasions be transmitted sexually, however, the low levels detected in genital secretions compared to saliva suggest that this is not a major transmission route. The finding of small quantities of cell-associated virus suggests a latent infection; thus EBV is probably in the B lymphocyte rather than in the epithelial cell component of the secretions.

Resting B cells as a transfer vehicle for Epstein-Barr virus infection of epithelial cells

Epstein-Barr virus (EBV), an orally transmitted herpesvirus, efficiently targets B lymphocytes through binding of the viral envelope glycoprotein gp350 to the complement receptor CD21. How the virus accesses epithelial cells is less well understood, because such cells are largely resistant to infection with cell-free virus in vitro. Here, we show that, after binding to primary B cells, most Epstein-Barr virions are not internalized but remain on the B cell surface and from there can transfer efficiently to CD21-negative epithelial cells, increasing epithelial infection by 10(3)- to 10(4)-fold compared with cell-free virus. Transfer infection is associated with the formation of B cell-epithelial conjugates with gp350/CD21 complexes focused at the intercellular synapse; transfer involves the gp85 and gp110 viral glycoproteins but is independent of gp42, the HLA class II ligand that is essential for B cell entry. Therefore, through efficient binding to the B cell surface, EBV has developed a means of simultaneously accessing both lymphoid and epithelial compartments; in particular, infection of pharyngeal epithelium by orally transmitted virus becomes independent of initial virus replication in the B cell system.

Epstein-Barr virus infection negatively impacts the CXCR4-dependent migration of tonsillar B cells

The primary Epstein-Barr virus (EBV) infection occurs in the oropharynx, where the virus infects B cells and subsequently establishes latency in the memory B-cell compartment. EBV has previously been shown to induce changes in the cell surface expression of several chemokine receptors in cell lines and the transfection of EBNA2 or LMP1 into a B-cell-lymphoma-derived cell line decreased the expression of CXCR4. We show that in vitro EBV infection reduces the expression of CXCR4 on primary tonsil B cells already 43 hr after infection. Furthermore, EBV infection affects the chemotactic response to stromal cell-derived factor (SDF-1)alpha/CXCL12, the ligand for CXCR4, with a reduction of SDF-1alpha-induced migration. To clarify whether this reduced migration is EBV-specific or a consequence of cell activation, tonsillar B cells were either infected with EBV, activated with anti-CD40 and interleukin-4 (IL-4) or kept in medium. Activation by anti-CD40 and IL-4 decreased the CXCR4 expression but the CD40 + IL-4-stimulated cells showed no reduction of chemotactic efficacy. Our finding suggests that changing the SDF-1alpha response of the EBV-infected B cells may serve the viral strategy by directing the infected cells into the extrafollicular areas, rather than retaining them in the lymphoepithelium.

Virus and cell RNAs expressed during Epstein-Barr virus replication

Changes in Epstein-Barr virus (EBV) and cell RNA levels were assayed following immunoglobulin G (IgG) cross-linking-induced replication in latency 1-infected Akata Burkitt B lymphoblasts. EBV replication as assayed by membrane gp350 expression was approximately 5% before IgG cross-linking and increased to more than 50% 48 h after induction. Seventy-two hours after IgG cross-linking, gp350-positive cells excluded propidium iodide as well as gp350-negative cells. EBV RNA levels changed temporally in parallel with previously defined sensitivity to inhibitors of protein or viral DNA synthesis. BZLF1 immediate-early RNA levels doubled by 2 h and reached a peak at 4 h, whereas BMLF1 doubled by 4 h with a peak at 8 h, and BRLF1 doubled by 8 h with peak at 12 h. Early RNAs peaked at 8 to 12 h, and late RNAs peaked at 24 h. Hybridization to intergenic sequences resulted in evidence for new EBV RNAs. Surprisingly, latency III (LTIII) RNAs for LMP1, LMP2, EBNALP, EBNA2, EBNA3A, EBNA3C, and BARTs were detected at 8 to 12 h and reached maxima at 24 to 48 h. EBNA2 and LMP1 were at full LTIII levels by 48 h and localized to gp350-positive cells. Thus, LTIII expression is a characteristic of late EBV replication in both B lymphoblasts and epithelial cells in immune-comprised people (J. Webster-Cyriaque, J. Middeldorp, and N. Raab-Traub, J. Virol. 74:7610-7618, 2000). EBV replication significantly altered levels of 401 Akata cell RNAs, of which 122 RNAs changed twofold or more relative to uninfected Akata cells. Mitogen-activated protein kinase levels were significantly affected. Late expression of LTIII was associated with induction of NF-kappaB responsive genes including IkappaBalpha and A20. The exclusion of propidium, expression of EBV LTIII RNAs and proteins, and up-regulation of specific cell RNAs are indicative of vital cell function late in EBV replication.