Epstein-Barr virus entry into cells

Alzheimer's disease as a viral disease: Revisiting the infectious hypothesis

Alzheimer's disease (AD) represents the most frequent type of dementia in elderly people. Two major forms of the disease exist: sporadic - the causes of which have not yet been fully understood - and familial - inherited within families from generation to generation, with a clear autosomal dominant transmission of mutations in Presenilin 1 (PSEN1), 2 (PSEN2) or Amyloid Precursors Protein (APP) genes. The main hallmark of AD consists of extracellular deposits of amyloid-beta (Aβ) peptide and intracellular deposits of the hyperphosphorylated form of the tau protein. An ever-growing body of research supports the viral infectious hypothesis of sporadic forms of AD. In particular, it has been shown that several herpes viruses (i.e., HHV-1, HHV-2, HHV-3 or varicella zoster virus, HHV-4 or Epstein Barr virus, HHV-5 or cytomegalovirus, HHV-6A and B, HHV-7), flaviviruses (i.e., Zika virus, Dengue fever virus, Japanese encephalitis virus) as well as Human Immunodeficiency Virus (HIV), hepatitis viruses (HAV, HBV, HCV, HDV, HEV), SARS-CoV2, Ljungan virus (LV), Influenza A virus and Borna disease virus, could increase the risk of AD. Here, we summarized and discussed these results. Based on these findings, significant issues for future studies are also put forward.

Markers of Epstein-Barr Virus Infection in Patients with Multiple Sclerosis

Viral infections have been suspected of being involved in the pathogenesis of certain autoimmune diseases for many years. Epstein-Barr virus (EBV), a DNA virus belonging to the Herpesviridae family, is thought to be associated with the onset and/or the progression of multiple sclerosis (MS), systemic lupus erythematosus, rheumatoid arthritis, Sjögren's syndrome and type 1 diabetes. The lifecycle of EBV consists of lytic cycles and latency programmes (0, I, II and III) occurring in infected B-cells. During this lifecycle, viral proteins and miRNAs are produced. This review provides an overview of the detection of EBV infection, focusing on markers of latency and lytic phases in MS. In MS patients, the presence of latency proteins and antibodies has been associated with lesions and dysfunctions of the central nervous system (CNS). In addition, miRNAs, expressed during lytic and latency phases, may be detected in the CNS of MS patients. Lytic reactivations of EBV can occur in the CNS of patients as well, with the presence of lytic proteins and T-cells reacting to this protein in the CNS of MS patients. In conclusion, markers of EBV infection can be found in MS patients, which argues in favour of a relationship between EBV and MS.

Bioinformatics analysis of the pathogenic link between Epstein-Barr virus infection, systemic lupus erythematosus and diffuse large B cell lymphoma

Epstein-Barr virus (EBV) is a risk factor for diffuse large B-cell lymphoma (DLBCL) and systemic lupus erythematosus (SLE). While prior research has suggested a potential correlation between SLE and DLBCL, the molecular mechanisms remain unclear. The present study aimed to explore the contribution of EBV infection to the pathogenesis of DLBCL in the individuals with SLE using bioinformatics approaches. The Gene Expression Omnibus database was used to compile the gene expression profiles of EBV-infected B cells (GSE49628), SLE (GSE61635), and DLBCL (GSE32018). Altogether, 72 shared common differentially expressed genes (DEGs) were extracted and enrichment analysis of the shared genes showed that p53 signaling pathway was a common feature of the pathophysiology. Six hub genes were selected using protein-protein interaction (PPI) network analysis, including CDK1, KIF23, NEK2, TOP2A, NEIL3 and DEPDC1, which showed preferable diagnostic values for SLE and DLBCL and involved in immune cell infiltration and immune responses regulation. Finally, TF-gene and miRNA-gene regulatory networks and 10 potential drugs molecule were predicted. Our study revealed the potential molecular mechanisms by which EBV infection contribute to the susceptibility of DLBCL in SLE patients for the first time and identified future biomarkers and therapeutic targets for SLE and DLBCL.

Epstein-Barr virus and multiple sclerosis

Epstein-Barr virus (EBV) is a ubiquitous human lymphotropic herpesvirus with a well-established causal role in several cancers. Recent studies have provided compelling epidemiological and mechanistic evidence for a causal role of EBV in multiple sclerosis (MS). MS is the most prevalent chronic inflammatory and neurodegenerative disease of the central nervous system and is thought to be triggered in genetically predisposed individuals by an infectious agent, with EBV as the lead candidate. How a ubiquitous virus that typically leads to benign latent infections can promote cancer and autoimmune disease in at-risk populations is not fully understood. Here we review the evidence that EBV is a causal agent for MS and how various risk factors may affect EBV infection and immune control. We focus on EBV contributing to MS through reprogramming of latently infected B lymphocytes and the chronic presentation of viral antigens as a potential source of autoreactivity through molecular mimicry. We consider how knowledge of EBV-associated cancers may be instructive for understanding the role of EBV in MS and discuss the potential for therapies that target EBV to treat MS.

Epstein-Barr Virus Genome Deletions in Epstein-Barr Virus-Positive T/NK Cell Lymphoproliferative Diseases

The main target cells for Epstein-Barr virus (EBV) infection and persistence are B lymphocytes, although T and NK cells can also become infected. In this paper, we characterize the EBV present in 21 pediatric and adult patients who were treated in France for a range of diseases that involve infection of T or NK cells. Of these 21 cases, 5 pediatric patients (21%) and 11 adult patients (52%) were of Caucasian origin. In about 30% of the cases, some of the EBV genomes contain a large deletion. The deletions are different in every patient but tend to cluster near the BART region of the viral genome. Detailed investigation of a family in which several members have persistent T or NK cell infection by EBV indicates that the virus genome deletions arise or are selected independently in each individual patient. Genome sequence polymorphisms in the EBV in these T or NK cell diseases reflect the geographic origin of the patient and not a distinct type of EBV (the 21 cases studied included examples of both type 1 and type 2 EBV infection). Using virus produced from type 1 or type 2 EBV genomes cloned in bacterial artificial chromosome (BAC) vectors, we demonstrate infection of T cells in cord blood from healthy donors. Our results are consistent with transient infection of some T cells being part of normal asymptomatic infection by EBV in young children. IMPORTANCE EBV contributes to several types of human cancer. Some cancers and nonmalignant lymphoproliferative diseases involving T or NK cells contain EBV. These diseases are relatively frequent in Japan and China and have been shown sometimes to have deletions in the EBV genome in the disease cells. We identify further examples of deletions within the EBV genome associated with T or NK cell diseases, and we provide evidence that the virus genomes with these deletions are most likely selected in the individual cases, rather than being transmitted between people during infection. We demonstrate EBV infection of cord blood T cells by highly characterized, cloned EBV genomes and suggest that transient infection of T cells may be part of normal asymptomatic infection by EBV in young children.

Advances in pathogenesis and precision medicine for nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a squamous carcinoma with apparent geographical and racial distribution, mostly prevalent in East and Southeast Asia, particularly concentrated in southern China. The epidemiological trend over the past decades has suggested a substantial reduction in the incidence rate and mortality rate due to NPC. These results may reflect changes in lifestyle and environment, and more importantly, a deeper comprehension of the pathogenic mechanism of NPC, leading to much progress in the preventing, screening, and treating for this cancer. Herein, we present the recent advances on the key signal pathways involved in pathogenesis of NPC, the mechanism of Epstein‐Barr virus (EBV) entry into the cell, and the progress of EBV vaccine and screening biomarkers. We will also discuss in depth the development of various therapeutic approaches including radiotherapy, chemotherapy, surgery, targeted therapy, and immunotherapy. These research advancements have led to a new era of precision medicine in NPC.

Epstein-Barr Virus-Associated Malignancies and Immune Escape: The Role of the Tumor Microenvironment and Tumor Cell Evasion Strategies

Simple Summary

The Epstein–Barr virus, also termed human herpes virus 4, is a human pathogenic double-stranded DNA virus. It is highly prevalent and has been linked to the development of 1–2% of cancers worldwide. EBV-associated malignancies encompass various structural and epigenetic alterations. In addition, EBV-encoded gene products and microRNAs interfere with innate and adaptive immunity and modulate the tumor microenvironment. This review provides an overview of the characteristic features of EBV with a focus on the intrinsic and extrinsic immune evasion strategies, which contribute to EBV-associated malignancies.

Abstract

The detailed mechanisms of Epstein–Barr virus (EBV) infection in the initiation and progression of EBV-associated malignancies are not yet completely understood. During the last years, new insights into the mechanisms of malignant transformation of EBV-infected cells including somatic mutations and epigenetic modifications, their impact on the microenvironment and resulting unique immune signatures related to immune system functional status and immune escape strategies have been reported. In this context, there exists increasing evidence that EBV-infected tumor cells can influence the tumor microenvironment to their own benefit by establishing an immune-suppressive surrounding. The identified mechanisms include EBV gene integration and latent expression of EBV-infection-triggered cytokines by tumor and/or bystander cells, e.g., cancer-associated fibroblasts with effects on the composition and spatial distribution of the immune cell subpopulations next to the infected cells, stroma constituents and extracellular vesicles. This review summarizes (i) the typical stages of the viral life cycle and EBV-associated transformation, (ii) strategies to detect EBV genome and activity and to differentiate various latency types, (iii) the role of the tumor microenvironment in EBV-associated malignancies, (iv) the different immune escape mechanisms and (v) their clinical relevance. This gained information will enhance the development of therapies against EBV-mediated diseases to improve patient outcome.

Targeting Host Cellular Factors as a Strategy of Therapeutic Intervention for Herpesvirus Infections

Herpesviruses utilize various host factors to establish latent infection, survival, and spread disease in the host. These factors include host cellular machinery, host proteins, gene expression, multiple transcription factors, cellular signal pathways, immune cell activation, transcription factors, cytokines, angiogenesis, invasion, and factors promoting metastasis. The knowledge and understanding of host genes, protein products, and biochemical pathways lead to discovering safe and effective antivirals to prevent viral reactivation and spread infection. Here, we focus on the contribution of pro-inflammatory, anti-inflammatory, and resolution lipid metabolites of the arachidonic acid (AA) pathway in the lifecycle of herpesvirus infections. We discuss how various herpesviruses utilize these lipid pathways to their advantage and how we target them to combat herpesvirus infection. We also summarize recent development in anti-herpesvirus therapeutics and new strategies proposed or under clinical trials. These anti-herpesvirus therapeutics include inhibitors blocking viral life cycle events, engineered anticancer agents, epigenome influencing factors, immunomodulators, and therapeutic compounds from natural extracts.

Modulation of Endosome Function, Vesicle Trafficking and Autophagy by Human Herpesviruses

Human herpesviruses are a ubiquitous family of viruses that infect individuals of all ages and are present at a high prevalence worldwide. Herpesviruses are responsible for a broad spectrum of diseases, ranging from skin and mucosal lesions to blindness and life-threatening encephalitis, and some of them, such as Kaposi’s sarcoma-associated herpesvirus (KSHV) and Epstein–Barr virus (EBV), are known to be oncogenic. Furthermore, recent studies suggest that some herpesviruses may be associated with developing neurodegenerative diseases. These viruses can establish lifelong infections in the host and remain in a latent state with periodic reactivations. To achieve infection and yield new infectious viral particles, these viruses require and interact with molecular host determinants for supporting their replication and spread. Important sets of cellular factors involved in the lifecycle of herpesviruses are those participating in intracellular membrane trafficking pathways, as well as autophagic-based organelle recycling processes. These cellular processes are required by these viruses for cell entry and exit steps. Here, we review and discuss recent findings related to how herpesviruses exploit vesicular trafficking and autophagy components by using both host and viral gene products to promote the import and export of infectious viral particles from and to the extracellular environment. Understanding how herpesviruses modulate autophagy, endolysosomal and secretory pathways, as well as other prominent trafficking vesicles within the cell, could enable the engineering of novel antiviral therapies to treat these viruses and counteract their negative health effects.

Host-virus interaction and viral evasion

With each infectious pandemic or outbreak, the medical community feels the need to revisit basic concepts of immunology to understand and overcome the difficult times brought about by these infections. Regarding viruses, they have historically been responsible for many deaths, and such a peculiarity occurs because they are known to be obligate intracellular parasites that depend upon the host's cell machinery for their replication. Successful infection with the production of essential viral components requires constant viral evolution as a strategy to manipulate the cellular environment, including host internal factors, the host's nonspecific and adaptive immune responses to viruses, the metabolic and energetic state of the infected cell, and changes in the intracellular redox environment during the viral infection cycle. Based on this knowledge, it is fundamental to develop new therapeutic strategies for controlling viral dissemination, by means of antiviral therapies, vaccines, or antioxidants, or by targeting the inhibition or activation of cell signaling pathways or metabolic pathways that are altered during infection. The rapid recovery of altered cellular homeostasis during viral infection is still a major challenge. Here, we review the strategies by which viruses evade the host's immune response and potential tools used to develop more specific antiviral therapies to cure, control, or prevent viral diseases.

A novel vaccine candidate based on chimeric virus-like particle displaying multiple conserved epitope peptides induced neutralizing antibodies against EBV infection

Rationale: Epstein-Barr virus (EBV) is the causative pathogen for infectious mononucleosis and many kinds of malignancies including several lymphomas such as Hodgkin's lymphoma, Burkitt's lymphoma and NK/T cell lymphoma as well as carcinomas such as nasopharyngeal carcinoma (NPC) and EBV-associated gastric carcinoma (EBV-GC). However, to date no available prophylactic vaccine was launched to the market for clinical use.

Methods: To develop a novel vaccine candidate to prevent EBV infection and diseases, we designed chimeric virus-like particles (VLPs) based on the hepatitis B core antigen (HBc149). Various VLPs were engineered to present combinations of three peptides derived from the receptor binding domain of EBV gp350. All the chimeric virus-like particles were injected into Balb/C mice for immunogenicity evaluation. Neutralizing titer of mice sera were detected using an in vitro cell model.

Results: All chimeric HBc149 proteins self-assembled into VLPs with gp350 epitopes displayed on the surface of spherical particles. Interestingly, the different orders of the three epitopes in the chimeric proteins induced different immune responses in mice. Two constructs (149-3A and 149-3B) induced high serum titer against the receptor-binding domain of gp350. Most importantly, these two VLPs elicited neutralizing antibodies in immunized mice, which efficiently blocked EBV infection in cell culture. Competition analysis showed that sera from these mice contained antibodies to a major neutralizing epitope recognized by the strong neutralizing mAb 72A1.

Conclusion: Our data demonstrate that HBc149 chimeric VLPs provide a valuable platform to present EBV gp350 antigens and offer a robust basis for the development of peptide-based candidate vaccines against EBV.

Alphaherpesvirus gB Homologs Are Targeted to Extracellular Vesicles, but They Differentially Affect MHC Class II Molecules

Herpesvirus envelope glycoprotein B (gB) is one of the best-documented extracellular vesicle (EVs)-incorporated viral proteins. Regarding the sequence and structure conservation between gB homologs, we asked whether bovine herpesvirus-1 (BoHV-1) and pseudorabies virus (PRV)-encoded gB share the property of herpes simplex-1 (HSV-1) gB to be trafficked to EVs and affect major histocompatibility complex (MHC) class II. Our data highlight some conserved and differential features of the three gBs. We demonstrate that mature, fully processed BoHV-1 and PRV gBs localize to EVs isolated from constructed stable cell lines and EVs-enriched fractions from virus-infected cells. gB also shares the ability to co-localize with CD63 and MHC II in late endosomes. However, we report here a differential effect of the HSV-1, BoHV-1, and PRV glycoprotein on the surface MHC II levels, and MHC II loading to EVs in stable cell lines, which may result from their adverse ability to bind HLA-DR, with PRV gB being the most divergent. BoHV-1 and HSV-1 gB could retard HLA-DR exports to the plasma membrane. Our results confirm that the differential effect of gB on MHC II may require various mechanisms, either dependent on its complex formation or on inducing general alterations to the vesicular transport. EVs from virus-infected cells also contained other viral glycoproteins, like gD or gE, and they were enriched in MHC II. As shown for BoHV-1 gB- or BoHV-1-infected cell-derived vesicles, those EVs could bind anti-virus antibodies in ELISA, which supports the immunoregulatory potential of alphaherpesvirus gB.

Epstein-Barr Virus Infection in the Development of Neurological Disorders

Epstein-Barr Virus (EBV) is a ubiquitous human herpesvirus that contributes to the etiology of diverse human cancers and auto-immune diseases. EBV establishes a relatively benign, long-term latent infection in over 90 percent of the adult population. Yet, it also increases risk for certain cancers and auto-immune disorders depending on complex viral, host, and environmental factors that are only partly understood. EBV latent infection is found predominantly in memory B-cells, but the natural infection cycle and pathological aberrations enable EBV to infect numerous other cell types, including oral, nasopharyngeal, and gastric epithelia, B-, T-, and NK-lymphoid cells, myocytes, adipocytes, astrocytes, and neurons. EBV infected cells, free virus, and gene products can also be found in the CNS. In addition to the direct effects of EBV on infected cells and tissue, the effect of chronic EBV infection on the immune system is also thought to contribute to pathogenesis, especially auto-immune disease. Here, we review properties of EBV infection that may shed light on its potential pathogenic role in neurological disorders.

Viral Infection of Human Natural Killer Cells

Natural killer (NK) cells are essential in the early immune response against viral infections, in particular through clearance of virus-infected cells. In return, viruses have evolved multiple mechanisms to evade NK cell-mediated viral clearance. Several unrelated viruses, including influenza virus, respiratory syncytial virus, and human immunodeficiency virus, can directly interfere with NK cell functioning through infection of these cells. Viral infection can lead to immune suppression, either by downregulation of the cytotoxic function or by triggering apoptosis, leading to depletion of NK cells. In contrast, some viruses induce proliferation or changes in the morphology of NK cells. In this review article, we provide a comprehensive overview of the viruses that have been reported to infect NK cells, we discuss their mechanisms of entry, and describe the interference with NK cell effector function and phenotype. Finally, we discuss the contribution of virus-infected NK cells to viral load. The development of specific therapeutics, such as viral entry inhibitors, could benefit from an enhanced understanding of viral infection of NK cells, opening up possibilities for the prevention of NK cell infection.

Human MHC-II with Shared Epitope Motifs Are Optimal Epstein-Barr Virus Glycoprotein 42 Ligands-Relation to Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disorder of unknown etiology, which is characterized by inflammation in the synovium and joint damage. Although the pathogenesis of RA remains to be determined, a combination of environmental (e.g., viral infections) and genetic factors influence disease onset. Especially genetic factors play a vital role in the onset of disease, as the heritability of RA is 50–60%, with the human leukocyte antigen (HLA) alleles accounting for at least 30% of the overall genetic risk. Some HLA-DR alleles encode a conserved sequence of amino acids, referred to as the shared epitope (SE) structure. By analyzing the structure of a HLA-DR molecule in complex with Epstein-Barr virus (EBV), the SE motif is suggested to play a vital role in the interaction of MHC II with the viral glycoprotein (gp) 42, an essential entry factor for EBV. EBV has been repeatedly linked to RA by several lines of evidence and, based on several findings, we suggest that EBV is able to induce the onset of RA in predisposed SE-positive individuals, by promoting entry of B-cells through direct contact between SE and gp42 in the entry complex.

A comparative review of viral entry and attachment during large and giant dsDNA virus infections

Viruses enter host cells via several mechanisms, including endocytosis, macropinocytosis, and phagocytosis. They can also fuse at the plasma membrane and can spread within the host via cell-to-cell fusion or syncytia. The mechanism used by a given viral strain depends on its external topology and proteome and the type of cell being entered. This comparative review discusses the cellular attachment receptors and entry pathways of dsDNA viruses belonging to the families Adenoviridae, Baculoviridae, Herpesviridae and nucleocytoplasmic large DNA viruses (NCLDVs) belonging to the families Ascoviridae, Asfarviridae, Iridoviridae, Phycodnaviridae, and Poxviridae, and giant viruses belonging to the families Mimiviridae and Marseilleviridae as well as the proposed families Pandoraviridae and Pithoviridae. Although these viruses have several common features (e.g., topology, replication and protein sequence similarities) they utilize different entry pathways to infect wide-range of hosts, including humans, other mammals, invertebrates, fish, protozoa and algae. Similarities and differences between the entry methods used by these virus families are highlighted, with particular emphasis on viral topology and proteins that mediate viral attachment and entry. Cell types that are frequently used to study viral entry are also reviewed, along with other factors that affect virus-host cell interactions.

B-Cell-Rich T-Cell Lymphoma Associated with Epstein-Barr Virus-Reactivation and T-Cell Suppression Following Antithymocyte Globulin Therapy in a Patient with Severe Aplastic Anemia

B-cell lymphoproliferative disorder (B-LPD) is generally characterized by the proliferation of Epstein-Barr virus (EBV)-infected B lymphocytes. We here report the development of EBV-negative B-LPD associated with EBV-reactivation following antithymocyte globulin (ATG) therapy in a patient with aplastic anemia. The molecular autopsy study showed the sparse EBV-infected clonal T cells could be critically involved in the pathogenesis of EBV-negative oligoclonal B-LPD through cytokine amplification and escape from T-cell surveillances attributable to ATG-based immunosuppressive therapy, leading to an extremely rare B-cell-rich T-cell lymphoma. This report helps in elucidating the complex pathophysiology of intractable B-LPD refractory to rituximab.

Effect of high dose vitamin C on Epstein-Barr viral infection

Background Many natural compounds were tested for the ability to suppress viral replication. The present manuscript details an analysis of high dose vitamin C therapy on patients with EBV infection. Material and Methods The data were obtained from the patient history database at the Riordan Clinic. Among people in our database who were treated with intravenous vitamin C (7.5 g to 50 g infusions) between 1997 and 2006, 178 patients showed elevated levels of EBV EA IgG (range 25 to 211 AU) and 40 showed elevated levels of EBV VCA IgM (range 25 to 140 AU). Most of these patients had a diagnosis of chronic fatigue syndrome, with the rest being diagnosed as having mononucleosis, fatigue, or EBV infection. Results Our data provide evidence that high dose intravenous vitamin C therapy has a positive effect on disease duration and reduction of viral antibody levels. Plasma levels of ascorbic acid and vitamin D were correlated with levels of antibodies to EBV. We found an inverse correlation between EBV VCA IgM and vitamin C in plasma in patients with mononucleosis and CFS meaning that patients with high levels of vitamin C tended to have lower levels of antigens in the acute state of disease. In addition, a relation was found between vitamin D levels and EBV EA IgG with lower levels of EBV early antigen IgG for higher levels of vitamin D. Conclusions The clinical study of ascorbic acid and EBV infection showed the reduction in EBV EA IgG and EBV VCA IgM antibody levels over time during IVC therapy that is consistent with observations from the literature that millimolar levels of ascorbate hinder viral infection and replication in vitro.

Entry of herpesviruses into cells: the enigma variations

The entry of herpesviruses into their target cells is complex at many levels. Virus entry proceeds by a succession of interactions between viral envelope glycoproteins and molecules on the cell membrane. The process is divided into distinct steps: attachment to the cell surface, interaction with a specific entry receptor, internalization of the particle (optional and cell specific), and membrane fusion. Several viral envelope glycoproteins are involved in one or several of these steps. The most conserved entry glycoproteins in the herpesvirus family (gB, gH/gL) are involved in membrane fusion. Around this functional core, herpesviruses have a variety of receptor binding glycoproteins, which interact with cell surface proteins often from different families. This interaction activates and controls the actual fusion machinery. Interactions with cellular receptors and between viral glycoproteins have to be tightly coordinated and regulated to guarantee successful entry. Although additional entry receptors for herpesviruses continue to be identified, the molecular interactions between viral glycoproteins remain mostly enigmatic. This chapter will review our current understanding of the molecular interactions that occur during herpesvirus entry from attachment to fusion. Particular emphasis will be placed on structure-based representation of receptor binding as a trigger of fusion during herpes simplex virus entry.

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.

Progress and problems in understanding and managing primary Epstein-Barr virus infections

Epstein-Barr virus (EBV) is a gammaherpesvirus that infects a large fraction of the human population. Primary infection is often asymptomatic but results in lifelong infection, which is kept in check by the host immune system. In some cases, primary infection can result in infectious mononucleosis. Furthermore, when host-virus balance is not achieved, the virus can drive potentially lethal lymphoproliferation and lymphomagenesis. In this review, we describe the biology of EBV and the host immune response. We review the diagnosis of EBV infection and discuss the characteristics and pathogenesis of infectious mononucleosis. These topics are approached in the context of developing therapeutic and preventative strategies.

Mapping regions of Epstein-Barr virus (EBV) glycoprotein B (gB) important for fusion function with gH/gL

Glycoproteins gB and gH/gL are required for entry of Epstein-Barr virus (EBV) into cells, but the role of each glycoprotein and how they function together to mediate fusion is unclear. Analysis of the functional homology of gB from the closely related primate gammaherpesvirus, rhesus lymphocryptovirus (Rh-LCV), showed that EBV gB could not complement Rh gB due to a species-specific dependence between gB and gL. To map domains of gB required for this interaction, we constructed a panel of EBV/Rh gB chimeric proteins. Analysis showed that insertion of Rh gB from residues 456 to 807 restored fusion function of EBV gB with Rh gH/gL, suggesting this region of gB is important for interaction with gH/gL. Split YFP bimolecular complementation (BiFC) provided evidence of an interaction between EBV gB and gH/gL. Together, our results suggest the importance of a gB-gH/gL interaction in EBV-mediated fusion with B cells requiring the region of EBV gB from 456 to 807.

beta1 integrin expression increases susceptibility of memory B cells to Epstein-Barr virus infection

Epstein-Barr virus (EBV) uses nasal mucosa-associated lymphoid tissue (NALT) as a portal of entry to establish life-long persistence in memory B cells. We previously showed that naïve and memory B cells from NALT are equally susceptible to EBV infection. Here we show that memory B cells from NALT are significantly more susceptible to EBV infection than those from remote lymphatic organs. We identify beta(1) integrin, which is expressed the most by naïve B cells of distinct lymphoid origin and by memory B cells from NALT, as a mediator of increased susceptibility to infection by EBV. Furthermore, we show that BMRF-2-beta(1) integrin interaction and the downstream signal transduction pathway are critical for postbinding events. An increase of beta(1) integrin expression in peripheral blood memory B cells provoked by CD40 stimulation plus B-cell receptor cross-linking increased the susceptibility of non-NALT memory B cells to EBV infection. Thus, EBV seems to utilize the increased activation status of memory B cells residing in the NALT to establish and ensure persistence.

Functional analysis of glycoprotein L (gL) from rhesus lymphocryptovirus in Epstein-Barr virus-mediated cell fusion indicates a direct role of gL in gB-induced membrane fusion

Glycoprotein L (gL), which complexes with gH, is a conserved herpesvirus protein that is essential for Epstein-Barr virus (EBV) entry into host cells. The gH/gL complex has a conserved role in entry among herpesviruses, yet the mechanism is not clear. To gain a better understanding of the role of gL in EBV-mediated fusion, chimeric proteins were made using rhesus lymphocryptovirus (Rh-LCV) gL (Rh gL), which shares a high sequence homology with EBV gL but does not complement EBV gL in mediating fusion with B cells. A reduction in fusion activity was observed with chimeric gL proteins that contained the amino terminus of Rh gL, although they retained their ability to process and transport gH/gL to the cell surface. Amino acids not conserved within this region in EBV gL when compared to Rh gL were further analyzed, with the results mapping residues 54 and 94 as being functionally important for EBV-mediated fusion. All chimeras and mutants displayed levels of cell surface expression similar to that of wild-type gL and interacted with gH and gp42. Our data also suggest that the role of gL involves the activation or recruitment of gB with the gH/gL complex, as we found that reduced fusion of Rh gL, EBV/Rh-LCV chimeras, and gL point mutants could be restored by replacing EBV gB with Rh gB. These observations demonstrate a distinction between the role of gL in the processing and trafficking of gH to the cell surface and a posttrafficking role in cell-cell fusion.

Cross-regulation between herpesviruses and the TNF superfamily members

Herpesviruses have evolved numerous strategies to subvert host immune responses so they can coexist with their host species. These viruses 'co-opt' host genes for entry into host cells and then express immunomodulatory genes, including mimics of members of the tumour-necrosis factor (TNF) superfamily, that initiate and alter host-cell signalling pathways. TNF superfamily members have crucial roles in controlling herpesvirus infection by mediating the direct killing of infected cells and by enhancing immune responses. Despite these strong immune responses, herpesviruses persist in a latent form, which suggests a dynamic relationship between the host immune system and the virus that results in a balance between host survival and viral control.

Distinct ex vivo susceptibility of B-cell subsets to epstein-barr virus infection according to differentiation status and tissue origin

Epstein-Barr virus (EBV) uses tonsils as the portal of entry to establish persistent infection. EBV is found in various B-cell subsets in tonsils but exclusively in memory B cells in peripheral blood. The in vitro susceptibilities of B-cell subsets to EBV infection have been studied solely qualitatively. In this work, we examined quantitatively the in vitro susceptibilities of various B-cell subsets from different tissue origins to EBV infection. First, we established a centrifugation-based inoculation protocol (spinoculation) that resulted in a significantly increased proportion of infected cells compared to that obtained by conventional inoculation, enabling a detailed susceptibility analysis. Importantly, B-cell infection occurred via the known EBV receptors and infected cells showed EBV mRNA expression patterns similar to those observed after conventional inoculation, validating our approach. Tonsillar naïve and memory B cells were infected ex vivo at similar frequencies. In contrast, memory B cells from blood, which represent B cells from various lymphoid tissues, were infected at lower frequencies than their naïve counterparts. Immunoglobulin A (IgA)-positive or IgG-positive tonsillar memory B cells were significantly more susceptible to EBV infection than IgM-positive counterparts. Memory B cells were transformed with lower efficiency than naïve B cells. This result was paralleled by lower proliferation rates. In summary, these data suggest that EBV exploits the B-cell differentiation status and tissue origin to establish persistent infection.

Characterization of EBV gB indicates properties of both class I and class II viral fusion proteins

To gain insight into Epstein-Barr virus (EBV) glycoprotein B (gB), recombinant, secreted variants were generated. The role of putative transmembrane regions, the proteolytic processing and the oligomerization state of the gB variants were investigated. Constructs containing 2 of 3 C-terminal hydrophobic regions were secreted, indicating that these do not act as transmembrane anchors. The efficiency of cleavage of the gB furin site was found to depend on the nature of C-terminus. All of the gB constructs formed rosette structures reminiscent of the postfusion aggregates formed by other viral fusion proteins. However, substitution of putative fusion loop residues, WY(112-113) and WLIY(193-196), with less hydrophobic amino acids from HSV-1 gB, produced trimeric protein and abrogated the ability of the EBV gB ectodomains to form rosettes. These data demonstrate biochemical features of EBV gB that are characteristic of other class I and class II viral fusion proteins, but not of HSV-1 gB.

Binding-site interactions between Epstein-Barr virus fusion proteins gp42 and gH/gL reveal a peptide that inhibits both epithelial and B-cell membrane fusion

Herpesviruses require membrane-associated glycoproteins gB, gH, and gL for entry into host cells. Epstein-Barr virus (EBV) gp42 is a unique protein also required for viral entry into B cells. Key interactions between EBV gp42 and the EBV gH/gL complex were investigated to further elucidate their roles in membrane fusion. Deletion and point mutants within the N-terminal region of gp42 revealed residues important for gH/gL binding and membrane fusion. Many five-residue deletion mutants in the N-terminal region of gp42 that exhibit reduced membrane fusion activity retain binding with gH/gL but map out two functional stretches between residues 36 and 96. Synthetic peptides derived from the gp42 N-terminal region were studied in in vitro binding experiments with purified gH/gL and in cell-cell fusion assays. A peptide spanning gp42 residues 36 to 81 (peptide 36-81) binds gH/gL with nanomolar affinity, comparable to full-length gp42. Peptide 36-81 efficiently inhibits epithelial cell membrane fusion and competes with soluble gp42 to inhibit B-cell fusion. Additionally, this peptide at low nanomolar concentrations inhibits epithelial cell infection by intact virus. Shorter gp42 peptides spanning the two functional regions identified by deletion mutagenesis had little or no binding to soluble gH/gL and were also unable to inhibit epithelial cell fusion, nor could they complement gp42 deletion mutants in B-cell fusion. These studies identify key residues of gp42 that are essential for gH/gL binding and membrane fusion activation, providing a nanomolar inhibitor of EBV-mediated membrane fusion.

Functional homology of gHs and gLs from EBV-related gamma-herpesviruses for EBV-induced membrane fusion

Epstein-Barr virus (EBV) is a human gamma-herpesvirus that primarily infects B lymphocytes and epithelial cells. Entry of EBV into B cells requires the viral glycoproteins gp42, gH/gL and gB, while gp42 is not necessary for infection of epithelial cells. In EBV, gH and gL form two distinct complexes, a bipartite complex that contains only gH and gL, used for infection of epithelial cells, and a tripartite complex that additionally includes gp42, used for infection of B cells. The gH/gL complex is conserved within the herpesvirus family, but its exact role in entry and mechanism of fusion is not yet known. To understand more about the functionality of EBVgH/gL, we investigated the functional homology of gHs and gLs from human herpesvirus 8 (HHV8) and two primate (rhesus and marmoset) gamma-herpesviruses in EBV-mediated virus-free cell fusion assay. Overall, gHs and gLs from the more homologous primate herpesviruses were better at complementing EBV gH and gL in fusion than HHV8 gH and gL. Interestingly, marmoset gH was able to complement fusion with epithelial cells, but not B cells. Further investigation of this led to the discovery that EBVgH is the binding partner of gp42 in the tripartite complex and the absence of fusion with B cells in the presence of marmoset gH/gL is due to its inability to bind gp42.

Soluble Epstein-Barr virus glycoproteins gH, gL, and gp42 form a 1:1:1 stable complex that acts like soluble gp42 in B-cell fusion but not in epithelial cell fusion

Epstein-Barr virus (EBV) is a herpesvirus that infects cells by fusing its lipid envelope with the target cell membrane. The fusion process requires the actions of viral glycoproteins gH, gL, and gB for entry into epithelial cells and additionally requires gp42 for entry into B cells. To further study the roles of these membrane-associated glycoproteins, purified soluble forms of gp42, gH, and gL were expressed that lack the membrane-spanning regions. The soluble gH/gL protein complex binds to soluble gp42 with high affinity, forming a stable heterotrimer with 1:1:1 stoichiometry, and this complex is not formed by an N-terminally truncated variant of gp42. The effects of adding soluble gp42, gH/gL, and gH/gL/gp42 were examined with a virus-free cell-cell fusion assay. The results demonstrate that, in contrast to gp42, membrane fusion does not proceed with secreted gH/gL. The addition of soluble gH/gL does not inhibit or enhance B-cell or epithelial cell fusion when membrane-bound gH/gL, gB, and gp42 are present. However, the soluble gH/gL/gp42 complex does activate membrane fusion with B cells, similarly to soluble gp42, but it does not inhibit fusion with epithelial cells, as observed for gp42 alone. A gp42 peptide, derived from an N-terminal segment involved in gH/gL interactions, binds to soluble gH/gL and inhibits EBV-mediated epithelial cell fusion, mimicking gp42. These observations reveal distinct functional requirements for gH/gL and gp42 complexes in EBV-mediated membrane fusion.

Epstein-Barr virus immunossuppression of innate immunity mediated by phagocytes

Epstein-Barr virus (EBV) is an oncogenic human herpesvirus that persistently infects approximately 90% of the world's population. Such a remarkably sustained of viral infectivity relies on EBV's ability to evade the host immune defenses. A crucial part of this anti-EBV response is mediated by cytotoxic CD8+ T lymphocytes, which maintain a life-long control over proliferating latently-infected B cells in order to prevent these from giving rise to lymphomatous diseases. On the other hand, little has been done to assess the role of phagocytes-mediated innate immunity in the pathogenesis of EBV infection. In the course of primary EBV infection, episodes of neutropenia and monocytopenia can be observed during the acute phase of infection. According to the role of those cells in the non specific and specific immunity, such a decrease in circulating phagocytes may then temporarily affect the immune defense and potentially influence the outcome of EBV infection. Recent studies have demonstrated that EBV infects both neutrophils and monocytes and modulates several of their biological functions. This review covers the current state of our knowledge relative to the role of neutrophils and monocytes in EBV pathogenesis and describes the nature of countermeasures deployed by EBV against these cells.

The amino terminus of Epstein-Barr virus glycoprotein gH is important for fusion with epithelial and B cells

Epstein-Barr virus (EBV) infects B lymphocytes and epithelial cells. While the glycoproteins required for entry into these two cell types differ, the gH/gL glycoprotein complex is essential for entry into both epithelial and B cells. Analysis of gH protein sequences from three gammaherpesviruses (EBV, marmoset, and rhesus) revealed a potential coiled-coil domain in the N terminus. Four leucines located in this region in EBV gH were replaced by alanines by site-directed mutagenesis and analyzed for cell-cell membrane fusion with B cells and epithelial cells. Reduction in fusion activity was observed for mutants containing L65A and/or L69A mutations, while substitutions in L55 and L74 enhanced the fusion activity of the mutant gH/gL complexes with both cell types. All of the mutants displayed levels of cell surface expression similar to those of wild-type gH and interacted with gL and gp42. The observation that a conservative mutation of leucine to alanine in the N terminus of EBV gH results in fusion-defective mutant gH/gL complexes is striking and points to an important role for this region in EBV-mediated membrane fusion with B lymphocytes and epithelial cells.

Association of viral factors with non-familial breast cancer in Taiwan by comparison with non-cancerous, fibroadenoma, and thyroid tumor tissues

To study the etiologic factors of non-familial breast cancer, the polymerase chain reaction (PCR) and Southern hybridization were used to detect six viruses including human papillomavirus (HPV), cytomegalovirus (CMV), Epstein-Barr virus (EBV), herpes simplex virus (HSV)-1, HSV-2, and human herpesvirus (HHV)-8 DNA in 69 patients with breast cancer and 60 specimens from non-cancerous or other individuals with thyroid tumors or fibroadenoma (non-breast cancer controls). Two specimens from patients with a familial history of breast cancer and five breast cancer specimens with negative results for beta-globin, which was used as internal control, were excluded from this study. Eight (12.9%) HSV-1, 28 (45.2%) EBV, 47 (75.8%) CMV, 8 (12.9%) HPV, and 28 (45.2%) HHV-8 positive samples out of the 62 breast cancer specimens were detected; no HSV-2 DNA was detected in any group. Among the viral gene-positive breast cancer samples, 12 (23.1%) were positive for 1 virus, 16 (30.8%) were positive for 2 viruses, 21 (40.4%) were positive for 3 viruses, and 3 (5.8%) were positive for 4 viruses. Among the viral gene-positive specimens of the control groups, only one virus, CMV, was found in the non-cancerous and thyroid tumor specimens, while multiple viruses were found in the fibroadenoma specimens. The viruses associated with breast cancer were HHV-8 > EBV (P <0.01). The viruses associated with fibroadenoma were HSV-1 and HHV-8 > EBV (P <0.01). The presence of more than one virus was found predominantly in breast cancer and exclusively found in fibroadenoma. CMV was the only virus associated with thyroid tumors.

Mutational analyses of Epstein-Barr virus glycoprotein 42 reveal functional domains not involved in receptor binding but required for membrane fusion

Epstein-Barr virus (EBV) is a human gammaherpesvirus associated with malignancies of both epithelial and lymphoid origin. Efficient infection of the latent host reservoir B lymphocytes involves the binding of glycoproteins gp350/220 for initial attachment, followed by the concerted action of gH, gL, gB, and gp42 for membrane fusion. The type II membrane protein gp42 is required for infection of B cells and assembles into a complex with gH and gL. The cellular host receptor for gp42, class II human leukocyte antigen (HLA), has been structurally verified by crystallization analyses of gp42 bound to HLA-DR1. Interestingly, the crystal structure revealed a hydrophobic pocket consisting of many aromatic and aliphatic residues from the predicted C-type lectin domain of gp42 that in other members of the C-type lectin family binds major histocompatibility complex class I or other diverse ligands. Although the hydrophobic pocket does not bind HLA class II, mutational analyses presented here indicate that this domain is essential for EBV-induced membrane fusion. In addition, mutational analysis of the region of gp42 contacting HLA class II in the gp42-HLA-DR1 cocrystal confirms that this region interacts with HLA class II and that this interaction is also important for EBV-induced membrane fusion.

Epstein-Barr Virus Infection of Human Natural Killer Cell Lines and Peripheral Blood Natural Killer Cells

Although considerable part of natural killer (NK) cell neoplasms possess EBV genome, there has been no direct evidence that EBV infects human NK cells in vitro. In this study, we demonstrated EBV entry into NK cells using a recombinant EBV, which contains enhanced green fluorescent protein (EGFP) gene in its genome (EGFP-EBV). After 48 h of exposure to EGFP-EBV, we detected EGFP signals in ∼30% of NK-92 and NKL cells and &gt;40% of peripheral blood NK cells from three healthy volunteers. Reverse transcription-PCR analysis of various EBV-associated genes confirmed EBV infection. In situ hybridization for EBERs and BHLFs showed that latent and lytic infections coexisted at the early phase of EBV infection in two NK cell lines. Although BHLF-positive cells in the early lytic phase were round-shaped, EBER-positive cells in latent EBV infection tended to show a bizarre shape. Flow cytometric analysis of EGFP-EBV-exposed NK cell lines showed that most of EBV-infected cells entered early apoptosis after 72 h of EBV exposure, which explains the difficulties to establish EBV-carrying NK clones. Flow cytometry and reverse transcription-PCR analysis indicated that two NK cell lines may fuse with EBV using HLA class II after binding to the virus through a distinct molecule from CD21. We established two EBV-carrying NKL clones showing latency types I and II, both of which are recognized in EBV-associated NK cell neoplasms. Because EBV-infected NKL cells showed only type I latency during the early phase of infection, the temporal profile of latent gene expression is similar to that of T cells. We first report in vitro EBV infection of human NK cells and establishment of EBV-carrying NK clones, which should contribute to elucidate the role of EBV in the development of NK cell neoplasms.

Evolution of cell recognition by viruses: a source of biological novelty with medical implications

The picture beginning to form from genome analyses of viruses, unicellular organisms, and multicellular organisms is that viruses have shared functional modules with cells. A process of coevolution has probably involved exchanges of genetic information between cells and viruses for long evolutionary periods. From this point of view present-day viruses show flexibility in receptor usage and a capacity to alter through mutation their receptor recognition specificity. It is possible that for the complex DNA viruses, due to a likely limited tolerance to generalized high mutation rates, modifications in receptor specificity will be less frequent than for RNA viruses, albeit with similar biological consequences once they occur. It is found that different receptors, or allelic forms of one receptor, may be used with different efficiency and receptor affinities are probably modified by mutation and selection. Receptor abundance and its affinity for a virus may modulate not only the efficiency of infection, but also the capacity of the virus to diffuse toward other sites of the organism. The chapter concludes that receptors may be shared by different, unrelated viruses and that one virus may use several receptors and may expand its receptor specificity in ways that, at present, are largely unpredictable.

Identification of proteins associated with murine gammaherpesvirus 68 virions

Murine gammaherpesvirus 68 (MHV68 [also known as gammaHV-68]) is distinguished by its ability to replicate to high titers in cultured cells, making it an excellent candidate for studying gammaherpesvirus virion composition. Extracellular MHV68 virions were isolated, and abundant virion-associated proteins were identified by mass spectrometry. Five nucleocapsid protein homologues, the tegument protein homologue encoded by open reading frame (ORF) 75c, and envelope glycoproteins B and H were detected. In addition, gene products from MHV68 ORF20, ORF24, ORF28, ORF45, ORF48, and ORF52 were identified in association with virions, suggesting that these gammaherpesvirus genes are involved in the early phase of infection or virion assembly and egress.

Cholesterol-dependent infection of Burkitt's lymphoma cell lines by Epstein–Barr virus

Epstein-Barr virus (EBV) infection is a multi-step process, first requiring virus binding to the host cell, followed by fusion of the viral envelope with the host cell plasma membrane. Efficient EBV entry into B cells requires, at the minimum, the interaction of the EBV-encoded glycoproteins gp350 with cellular CD21 and gp42 with MHC class II proteins. In this study, use of the cholesterol-binding drugs methyl-beta-cyclodextrin and nystatin efficiently inhibited EBV infection of target Burkitt's lymphoma B-cell lines, indicating an important role for cholesterol and suggesting the involvement of lipid rafts in EBV infection.

Epstein-Barr virus: induction and control of cell transformation

Epstein-Barr virus (EBV), a ubiquitous human herpes virus, is associated with an increasing number of lymphoid and epithelial malignancies. The ability of the virus to establish life-long persistent infections and induce growth transformation is related to the function of a set of viral proteins that are variously expressed in both normal and malignant cells. Recent evidence indicates that these viral proteins are able to usurp cellular pathways that promote the cell growth and survival, while impairing anti-viral immune responses. Elucidation of the mechanisms by which EBV induces cell transformation and escapes host immune control provides the rational background for the design of new strategies of intervention for EBV-related malignancies.

Gamma herpesviruses: pathogenesis of infection and cell signaling

Altered cell signaling is the molecular basis for cell proliferation occurring in association with several gamma herpesvirus infections. Three gamma herpesviruses, namely EBV/HHV-4, KSHV/HHV-8 and the MHV-68 (and/or MHV-72) and their unusual cell-pirated gene products are discussed in this respect. The EBV, KSHV as well as the MHV DNA may persist lifelong in an episomal form in the host carrier cells (mainly in lymphocytes but also in macrophages, in non-hornifying squamous epithelium and/or in blood vessel endothelial cells). Under conditions of extremely limited transcription, the EBV-infected cells express EBNA1 (EB nuclear antigen 1), the KSHV infected cells express LANA1 (latent nuclear antigen 1), while the MHV DNA carrier cells express the latency-associated protein M2. With the full set of latency-associated proteins expressed, EBV carrier cells synthesize additional EBNAs and at least one LMP (latent membrane protein 1). The latent KSHV carrier cells, in addition to LANA1, may express a viral cyclin, a viral Fas-DD-like ICE inhibitor protein (vFLIP) and a virus-specific transformation protein called kaposin (K12). In MHV latency with a wide expression of latency-associated proteins, the carrier cells express a LANA analogue (ORF73), the M3 protein, the K3/IE (immediate early) proteins and M11/bcl-2 homologue proteins. During the period of limited gene expression, the latency-associated proteins serve mainly for the maintenance of the latent episomal DNA (a typical example is EBNA1). In contrast, during latency with a broader spectrum gene expression, the virus-encoded products activate transcription of otherwise silenced cellular genes, which leads to the synthesis of enzymes capable of promoting not only viral but also cellular DNA replication. Thus, the latency-associated proteins block apoptosis and drive host cells towards division and immortalization. Proliferation of hemopoetic cells, which had become gamma herpesvirus DNA carriers, can be initiated and strongly enhanced in the presence of inflammatory cytokines and by virus-encoded analogues of interleukins, chemokines and IFN regulator proteins. At early stages of tumor formation, many proliferating hemopoetic and/or endothelium cells, which had became transcriptionally active under the influence of chemokines and cytokines, may not yet be infected. In contrast, at later stages of oncogenesis, the virus-encoded proteins, inducing false signaling and activating the proliferation pathways, bring the previously infected cells into full transformation burst.

Genetic and epigenetic changes in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a malignancy with remarkable racial and geographic distribution. The development of this EBV-associated cancer likely involves cumulative genetic and epigenetic changes in a background of predisposed genetic and environmental factors. Genome-wide studies have unravelled multiple chromosomal abnormalities with involvement of specific oncogenes and tumour suppressor genes. Alterations of genes such as Ras association domain family 1A (RASSF1A), p16/INK4A, p14/ARF suggest that multiple cellular pathways were dysregulated in the NPC cells. Studies on the precancerous lesions revealed early genetic changes and a critical role of EBV latent infection in the development of this cancer. Based on the existing findings, a pathogenetic model for NPC is proposed.

Immunological aspects of Epstein-Barr virus infection

Epstein-Barr virus (EBV) is a member of ubiquitous gamma herpes viruses, which primarily induces acute infectious mononucleosis (IM) or subclinical infection in susceptible subjects. The host reactions account for the clinical manifestation of IM. This virus also contributes to the development of lymphoid or epithelial malignancies. The outgrowth of EBV-infected B-cells is first controlled by interferon (IFN)-gamma and natural killer (NK) cells, and later by EBV-specific cytotoxic T-lymphocytes (CTL). To overcome the host responses and establish the persistent infection, EBV conducts the protean strategies of immune evasion. Several EBV genes modulate apoptotic signals and cytokine balances to persist B-cell infection without insulting the host. Uncontrolled lymphoproliferation occurs as EBV(+) B-cell lymphoproliferative disease (LPD)/lymphoma in AIDS, posttransplant, or primary immunodeficiency diseases (PID). On the other hand, EBV(+) T/NK cells are involved in EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH) or chronic active EBV infection (CAEBV) in children having no underlying immunodeficiencies, and at times lead to the clonal evolution of T/NK-cell LPD/lymphomas. Recent advance in molecular techniques has enabled us to analyze the clonality of EBV-infected lymphocytes and to quantify the gene expression of EBV and cytokines. Dominant autocrine loop of T helper (Th) 2 and Th1 may exert in EBV(+) B-LPD and T-LPD, respectively. Intensive studies on the immunological interface between effector components and EBV(+) target cells will provide more information on clarifying the pathogenesis of EBV-associated lymphoid malignancies, as well as on exploiting the therapeutic and preventive strategies for the formidable EBV-associated disease in childhood.

Structure of the Epstein-Barr virus gp42 protein bound to the MHC class II receptor HLA-DR1

Epstein-Barr virus (EBV) causes infectious mononucleosis, establishes long-term latent infections, and is associated with a variety of human tumors. The EBV gp42 glycoprotein binds MHC class II molecules, playing a critical role in infection of B lymphocytes. EBV gp42 belongs to the C-type lectin superfamily, with homology to NK receptors of the immune system. We report the crystal structure of gp42 bound to the human MHC class II molecule HLA-DR1. The gp42 binds HLA-DR1 using a surface site that is distinct from the canonical lectin and NK receptor ligand binding sites. At the canonical ligand binding site, gp42 forms a large hydrophobic groove, which could interact with other ligands necessary for EBV entry, providing a mechanism for coupling MHC recognition and membrane fusion.

Different functional domains in the cytoplasmic tail of glycoprotein B are involved in Epstein-Barr virus-induced membrane fusion

A virus-free cell fusion assay relying on the transient transfection of Epstein-Barr virus (EBV) glycoproteins into cells provides an efficient and quantitative assay for characterizing the viral requirements necessary for fusion of the viral envelope with the B cell membrane. Extensive cellular fusion occurred when Daudi cells were layered onto Chinese hamster ovary K1 cells transiently expressing EBV glycoproteins gp42, gH, gL, and gB. This is the first direct evidence that gB is involved in the process of EBV entry. Moreover, mutational analysis of gB indicates that the cytoplasmic tail contains two distinct domains that function differentially in the process of fusion. The region from amino acids 802 to 816 is necessary for productive membrane fusion, while amino acids 817 to 841 comprise a domain that negatively regulates membrane fusion.