Characterization of an Epstein-Barr virus receptor on human epithelial cells

Epstein Barr Virus: Development of Vaccines and Immune Cell Therapy for EBV-Associated Diseases

Epstein-Barr virus (EBV) is the first human tumor virus discovered and is strongly implicated in the etiology of multiple lymphoid and epithelial cancers. Each year EBV associated cancers account for over 200,000 new cases of cancer and cause 150,000 deaths world-wide. EBV is also the primary cause of infectious mononucleosis, and up to 70% of adolescents and young adults in developed countries suffer from infectious mononucleosis. In addition, EBV has been shown to play a critical role in the pathogenesis of multiple sclerosis. An EBV prophylactic vaccine that induces neutralizing antibodies holds great promise for prevention of EBV associated diseases. EBV envelope proteins including gH/gL, gB and gp350 play key roles in EBV entry and infection of target cells, and neutralizing antibodies elicited by each of these proteins have shown to prevent EBV infection of target cells and markedly decrease EBV titers in the peripheral blood of humanized mice challenged with lethal dose EBV. Recent studies demonstrated that immunization with the combination of gH/gL, gB and/or gp350 induced markedly increased synergistic EBV neutralizing activity compared to immunization with individual proteins. As previous clinical trials focused on gp350 alone were partially successful, the inclusion of gH/gL and gB in a vaccine formulation with gp350 represents a promising approach of EBV prophylactic vaccine development. Therapeutic EBV vaccines have also been tested clinically with encouraging results. Immunization with various vaccine platforms expressing the EBV latent proteins EBNA1, LMP1, and/or LMP2 promoted specific CD4+ and CD8+ cytotoxic responses with anti-tumor activity. The addition of EBV envelope proteins gH/gL, gB and gp350 has the potential to increase the efficacy of a therapeutic EBV vaccine. The immune system plays a critical role in the control of tumors, and immune cell therapy has emerged as a promising treatment of cancers. Adoptive T-cell therapy has been successfully used in the prevention and treatment of post-transplant lymphoproliferative disorder. Chimeric antigen receptor T cell therapy and T cell receptor engineered T cell therapy targeting EBV latent proteins LMP1, LMP2 and/or EBNA1 have been in development, with the goal to increase the specificity and efficacy of treatment of EBV associated cancers.

Immunization with Epstein-Barr Virus Core Fusion Machinery Envelope Proteins Elicit High Titers of Neutralizing Activities and Protect Humanized Mice from Lethal Dose EBV Challenge

Epstein–Barr virus (EBV) is the primary cause of infectious mononucleosis and is strongly implicated in the etiology of multiple lymphoid and epithelial cancers. EBV core fusion machinery envelope proteins gH/gL and gB coordinately mediate EBV fusion and entry into its target cells, B lymphocytes and epithelial cells, suggesting these proteins could induce antibodies that prevent EBV infection. We previously reported that the immunization of rabbits with recombinant EBV gH/gL or trimeric gB each induced markedly higher serum EBV-neutralizing titers for B lymphocytes than that of the leading EBV vaccine candidate gp350. In this study, we demonstrated that immunization of rabbits with EBV core fusion machinery proteins induced high titer EBV neutralizing antibodies for both B lymphocytes and epithelial cells, and EBV gH/gL in combination with EBV trimeric gB elicited strong synergistic EBV neutralizing activities. Furthermore, the immune sera from rabbits immunized with EBV gH/gL or trimeric gB demonstrated strong passive immune protection of humanized mice from lethal dose EBV challenge, partially or completely prevented death respectively, and markedly decreased the EBV load in peripheral blood of humanized mice. These data strongly suggest the combination of EBV core fusion machinery envelope proteins gH/gL and trimeric gB is a promising EBV prophylactic vaccine.

Unraveling the role of membrane microdomains during microbial infections

Infectious diseases pose major socioeconomic and health-related threats to millions of people across the globe. Strategies to combat infectious diseases derive from our understanding of the complex interactions between the host and specific bacterial, viral, and fungal pathogens. Lipid rafts are membrane microdomains that play important role in life cycle of microbes. Interaction of microbial pathogens with host membrane rafts influences not only their initial colonization but also their spread and the induction of inflammation. Therefore, intervention strategies aimed at modulating the assembly of membrane rafts and/or regulating raft-directed signaling pathways are attractive approaches for the. management of infectious diseases. The current review discusses the latest advances in terms of techniques used to study the role of membrane microdomains in various pathological conditions and provides updated information regarding the role of membrane rafts during bacterial, viral and fungal infections.

Designing an effective vaccine to prevent Epstein-Barr virus-associated diseases: challenges and opportunities

INTRODUCTION

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus associated with a number of clinical manifestations. Primary EBV infection in young adolescents often manifests as acute infectious mononucleosis and latent infection is associated with multiple lymphoid and epithelial cancers and autoimmune disorders, particularly multiple sclerosis. Areas covered: Over the last decade, our understanding of pathogenesis and immune regulation of EBV-associated diseases has provided an important platform for the development of novel vaccine formulations. In this review, we discuss developmental strategies for prophylactic and therapeutic EBV vaccines which have been assessed in preclinical and clinical settings. Expert commentary: Major roadblocks in EBV vaccine development include no precise understanding of the clinical correlates of protection, uncertainty about adjuvant selection and the unavailability of appropriate animal models. Recent development of new EBV vaccine formulations provides exciting opportunities for the formal clinical assessment of novel formulations.

Epstein-Barr Virus Infection of Mammary Epithelial Cells Promotes Malignant Transformation

Whether the human tumor virus, Epstein-Barr Virus (EBV), promotes breast cancer remains controversial and a potential mechanism has remained elusive. Here we show that EBV can infect primary mammary epithelial cells (MECs) that express the receptor CD21. EBV infection leads to the expansion of early MEC progenitor cells with a stem cell phenotype, activates MET signaling and enforces a differentiation block. When MECs were implanted as xenografts, EBV infection cooperated with activated Ras and accelerated the formation of breast cancer. Infection in EBV-related tumors was of a latency type II pattern, similar to nasopharyngeal carcinoma (NPC). A human gene expression signature for MECs infected with EBV, termed EBVness, was associated with high grade, estrogen-receptor-negative status, p53 mutation and poor survival. In 11/33 EBVness-positive tumors, EBV-DNA was detected by fluorescent in situ hybridization for the viral LMP1 and BXLF2 genes. In an analysis of the TCGA breast cancer data EBVness correlated with the presence of the APOBEC mutational signature. We conclude that a contribution of EBV to breast cancer etiology is plausible, through a mechanism in which EBV infection predisposes mammary epithelial cells to malignant transformation, but is no longer required once malignant transformation has occurred.

Rabbits immunized with Epstein-Barr virus gH/gL or gB recombinant proteins elicit higher serum virus neutralizing activity than gp350

Epstein-Barr virus (EBV) is the primary cause of infectious mononucleosis and has been strongly implicated in the etiology of multiple epithelial and lymphoid cancers, such as nasopharyngeal carcinoma, gastric carcinoma, Hodgkin lymphoma, Burkitt lymphoma, non-Hodgkin lymphoma and post-transplant lymphoproliferative disorder. There is currently no licensed prophylactic vaccine for EBV. Most efforts to develop prophylactic vaccines have focused on EBV gp350, which binds to CD21/CD35 to gain entry into B cells, and is a major target of serum neutralizing antibody in EBV seropositive humans. However, a recombinant monomeric gp350 protein failed to prevent EBV infection in a phase II clinical trial. Thus, alternative or additional target antigens may be necessary for a successful prophylactic vaccine. EBV gH/gL and gB proteins coordinately mediate EBV fusion and entry into B cells and epithelial cells, strongly suggesting that vaccination with these proteins might elicit antibodies that will prevent EBV infection. We produced recombinant trimeric and monomeric EBV gH/gL heterodimeric proteins and a trimeric EBV gB protein, in addition to tetrameric and monomeric gp350(1-470) proteins, in Chinese hamster ovary cells. We demonstrated that vaccination of rabbits with trimeric and monomeric gH/gL, trimeric gB, and tetrameric gp350(1-470) induced serum EBV-neutralizing titers, using cultured human B cells, that were >100-fold, 20-fold, 18-fold, and 4-fold higher, respectively, than monomeric gp350(1-470). These data strongly suggest a role for testing EBV gH/gL and EBV gB in a future prophylactic vaccine to prevent EBV infection of B cells, as well as epithelial cells.

Epstein- Barr Virus: Clinical and Epidemiological Revisits and Genetic Basis of Oncogenesis

Epstein-Barr virus (EBV) is classified as a member in the order herpesvirales, family herpesviridae, subfamily gammaherpesvirinae and the genus lymphocytovirus. The virus is an exclusively human pathogen and thus also termed as human herpesvirus 4 (HHV4). It was the first oncogenic virus recognized and has been incriminated in the causation of tumors of both lymphatic and epithelial nature. It was reported in some previous studies that 95% of the population worldwide are serologically positive to the virus. Clinically, EBV primary infection is almost silent, persisting as a life-long asymptomatic latent infection in B cells although it may be responsible for a transient clinical syndrome called infectious mononucleosis. Following reactivation of the virus from latency due to immunocompromised status, EBV was found to be associated with several tumors. EBV linked to oncogenesis as detected in lymphoid tumors such as Burkitt's lymphoma (BL), Hodgkin's disease (HD), post-transplant lymphoproliferative disorders (PTLD) and T-cell lymphomas (e.g. Peripheral T-cell lymphomas; PTCL and Anaplastic large cell lymphomas; ALCL). It is also linked to epithelial tumors such as nasopharyngeal carcinoma (NPC), gastric carcinomas and oral hairy leukoplakia (OHL). In vitro, EBV many studies have demonstrated its ability to transform B cells into lymphoblastoid cell lines (LCLs). Despite these malignancies showing different clinical and epidemiological patterns when studied, genetic studies have suggested that these EBV- associated transformations were characterized generally by low level of virus gene expression with only the latent virus proteins (LVPs) upregulated in both tumors and LCLs. In this review, we summarize some clinical and epidemiological features of EBV- associated tumors. We also discuss how EBV latent genes may lead to oncogenesis in the different clinical malignancies

Neuropilin 1 is an entry factor that promotes EBV infection of nasopharyngeal epithelial cells

Epstein-Barr virus (EBV) is implicated as an aetiological factor in B lymphomas and nasopharyngeal carcinoma. The mechanisms of cell-free EBV infection of nasopharyngeal epithelial cells remain elusive. EBV glycoprotein B (gB) is the critical fusion protein for infection of both B and epithelial cells, and determines EBV susceptibility of non-B cells. Here we show that neuropilin 1 (NRP1) directly interacts with EBV gB(23-431). Either knockdown of NRP1 or pretreatment of EBV with soluble NRP1 suppresses EBV infection. Upregulation of NRP1 by overexpression or EGF treatment enhances EBV infection. However, NRP2, the homologue of NRP1, impairs EBV infection. EBV enters nasopharyngeal epithelial cells through NRP1-facilitated internalization and fusion, and through macropinocytosis and lipid raft-dependent endocytosis. NRP1 partially mediates EBV-activated EGFR/RAS/ERK signalling, and NRP1-dependent receptor tyrosine kinase (RTK) signalling promotes EBV infection. Taken together, NRP1 is identified as an EBV entry factor that cooperatively activates RTK signalling, which subsequently promotes EBV infection in nasopharyngeal epithelial cells.

The role of inflammation in HPV infection of the Oesophagus

BACKGROUND

Several human cancers are known to be associated with inflammation and/or viral infections. However, the influence of tumour-related inflammation on viral uptake is largely unknown. In this study we used oesophageal squamous cell carcinoma (OSCC) as a model system since this type of cancer is associated with chronic irritation, inflammation and viral infections. Although still debated, the most important viral infection seems to be with Human Papillomavirus (HPV). The present study focused on a possible correlation between inflammation, OSCC development and the influence of HPV infection.

METHODS

A total of 114 OSCC biopsies and corresponding normal tissue were collected at Groote Schuur Hospital and Tygerberg Hospital, Cape Town (South Africa), that were subjected to RNA and DNA isolation. RNA samples were analysed by quantitative Light Cycler RT-PCR for the expression of selected genes involved in inflammation and infection, while conventional PCR was performed on the DNA samples to assess the presence of integrated viral DNA. Further, an in vitro infection assay using HPV pseudovirions was established to study the influence of inflammation on viral infectivity using selected cell lines.

RESULTS

HPV DNA was found in about 9% of OSCC patients, comprising predominantly the oncogenic type HPV18. The inflammatory markers IL6 and IL8 as well as the potential HPV receptor ITGA6 were significantly elevated while IL12A was downregulated in the tumour tissues. However, none of these genes were expressed in a virus-dependent manner. When inflammation was mimicked with various inflammatory stimulants such as benzo-α-pyrene, lipopolysaccharide and peptidoglycan in oesophageal epithelial cell lines in vitro, HPV18 pseudovirion uptake was enhanced only in the benzo-α-pyrene treated cells. Interestingly, HPV pseudovirion infectivity was independent of the presence of the ITGA6 receptor on the surface of the tested cells.

CONCLUSION

This study showed that although the carcinogen benzo-α-pyrene facilitated HPV pseudovirion uptake into cells in culture, HPV infectivity was independent of inflammation and seems to play only a minor role in oesophageal cancer.

Expression of complement receptors 1 (CR1/CD35) and 2 (CR2/CD21), and co-signaling molecule CD19 in cattle

C3d is a sub-fragment of the C3 component of the complement system. Covalent binding of multiple C3ds to antigen reduces the activation threshold of cognate B lymphocytes by one thousand fold through co-ligation of the B cell antigen receptor (BCR) and complement receptor 2 (CR2/CD21). Reverse transcriptase polymerase chain reaction (RT-PCR) revealed that, in cattle, four distinct complement receptors are produced from the Cr2 gene by alternative splicing. Cattle express two major variants of the Cr2 gene representing homologues of murine CR1 and CR2, each of which is expressed in both a long and a short form. Expression of CR1 and CR2 was detected in IgM(+) cells from both the spleen and peripheral blood. Additionally, the coding sequence of CD19, the CR2 co-signaling molecule, was determined. CD19 was confirmed to be expressed by IgM(+) cells from the spleen and peripheral blood.

Function of membrane rafts in viral lifecycles and host cellular response

Membrane rafts are small (10–200 nm) sterol- and sphingolipid-enriched domains that compartmentalize cellular processes. Membrane rafts play an important role in viral infection cycles and viral virulence. Viruses are divided into four main classes, enveloped DNA virus, enveloped RNA virus, nonenveloped DNA virus, and nonenveloped RNA virus. General virus infection cycle is also classified into two sections, the early stage (entry process) and the late stage (assembly, budding, and release processes of virus particles). In the viral cycle, membrane rafts act as a scaffold of many cellular signal transductions, which are associated with symptoms caused by viral infections. In this paper, we describe the functions of membrane rafts in viral lifecycles and host cellular response according to each virus classification, each stage of the virus lifecycle, and each virus-induced signal transduction.

Laser-capture microdissection of oropharyngeal epithelium indicates restriction of Epstein-Barr virus receptor/CD21 mRNA to tonsil epithelial cells

BACKGROUND

Epstein-Barr virus colonizes the oropharynx of a majority of individuals. It infects B lymphocytes and epithelial cells and can contribute to the development of both lymphoid and epithelial tumors. The virus uses CD21 for attachment to B cells which constitutively express the protein. Infection of epithelial cells in vitro is also more efficient if CD21 is available. However, its potential contribution to infection in vivo has been difficult to evaluate as discrepant results with antibodies have made it difficult to determine which, if any, epithelial cells in the oropharynx express CD21.

METHODS

To reevaluate CD21 expression by an alternative method, epithelial cells were isolated by laser-capture microdissection from formalin-fixed sections of tissues from various parts of the oropharynx and mRNA was amplified with primers specific for the exons of CD21 which code for the Epstein-Barr virus binding site.

RESULTS

CD21 mRNA was expressed in tonsil epithelium, but not in epithelium from buccal mucosa, uvula, soft palate or tongue.

CONCLUSIONS

CD21 does not contribute to infection of most normal epithelial tissues in the oropharynx, but may contribute to infection of epithelial cells in the tonsil, where virus has been demonstrated in healthy carriers.

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.

Extended flexible linker structures in the complement chimaeric conjugate CR2-Ig by scattering, analytical ultracentrifugation and constrained modelling: implications for function and therapy

Complement receptor 2 (CR2; CD21) is a membrane-bound regulator of complement activation, being comprised of 15 or 16 short complement repeat (SCR) domains. A recombinant glycosylated human CR2 SCR 1-2 domain pair was engineered with the Fc fragment of a mouse IgG1 antibody to create a chimaera CR2-Ig containing the major ligand binding domains. Such a chimaera has therapeutic potential as a complement inhibitor or immune modulator. X-ray and neutron scattering and analytical ultracentrifugation identified its domain structure in solution, and provided a comparison with controversial folded-back crystal structures for deglycosylated CR2 SCR 1-2. The radius of gyration R(G) of CR2-Ig was determined to be 5.39(+/-0.14) nm and 5.29(+/-0.01) nm by X-ray and neutron scattering, respectively. The maximum dimension of CR2-Ig was determined to be 17 nm. The molecular mass of CR2-Ig ranged between 101,000 Da and 107,000 Da as determined by neutron scattering and sedimentation equilibrium, in good agreement with the sequence-derived value of 106,600 Da. Sedimentation velocity gave a sedimentation coefficient of 4.49(+/-0.11) S. Stereochemically complete models for CR2-Ig were constructed from crystal structures for the CR2 SCR 1-2 and mouse IgG1 Fc fragments. The two SCR domains and the Fc fragment were joined by randomised conformational peptides. The analysis of 35,000 possible CR2-Ig models showed that only those models in which the two SCR domains were arranged in an open V-shape in random orientations about the Fc fragment accounted for the scattering and sedimentation data. It was not possible to define one single conformational family of Fab-like fragment relative to the Fc fragment. This flexibility is attributed to the relatively long linker sequence and the absence of the antibody light chain from CR2-Ig. The modelling also confirmed that the structure of CR2 SCR 1-2 is more extended in solution than in its crystal structure.

A B-lymphocyte binding peptide from BNRF1 induced antibodies inhibiting EBV-invasion of B-lymphocytes

Epstein-Barr virus (EBV) infects human target cells mainly through gp350/220-CD21 and gp42-MHCII interactions; however, it has been shown that these interactions are dispensable for EBV-invasion of susceptible cells, suggesting that other viral proteins are involved in this process. It is probable that tegument BNRF1/p140 protein is involved in EBV-invasion of target cells, since anti-p140 antibodies inhibit EBV-infection of B-lymphocytes and there is evidence that part of the protein is located on virus surface. Sixty-six peptides, covering the entire BNRF1/p140 sequence, were synthesised and tested in lymphoblastoid cell line binding assays. Peptides 11465 and 11521 bound with high affinity to Raji, Ramos and P3HR-1 cells but not to erythrocytes, showing cell-binding behaviour similar to EBV. These two peptides induced antibodies recognising live EBV-infected cells. Interestingly, peptide-11521 (YVLQNAHQIACHFHSNGTDA) or antibodies induced by this peptide inhibited EBV-binding to B-lymphocytes, suggesting that this p140-region could be involved in EBV and B-lymphocyte interaction.

Identifying gp85-regions involved in Epstein-Barr virus binding to B-lymphocytes

Epstein-Barr virus lacking glycoprotein gp85 cannot infect B-cells and epithelial cells. The gp85 belongs to the molecular complex required for virus invasion of B-lymphocyte or epithelial cells. Moreover, there is evidence that gp85 is necessary for virus attachment to epithelial cells. Thirty-six peptides from the entire gp85-sequence were tested in epithelial and lymphoblastoid cell line binding assays to identify gp85-regions involved in virus-cell interaction. Five of these peptides presented high binding activity to Raji, Ramos, P3HR-1, and HeLa cells, but not to erythrocytes; Raji-cell affinity constants were between 80 and 140nM. Of these five peptides, 11435 ((181)TYKRVTEKGDEHVLSLVFGK(200)), 11436 ((201)TKDLPDLRGPFSYPSLTSAQ(220)), and 11438 ((241)YFVPNLKDMFSRAVTMTAAS(260)) bound to a 65kDa protein on Raji-cell surface. These peptides and antibodies induced by them (recognising live EBV-infected cells) inhibited Epstein-Barr virus interaction with cord blood lymphocytes. It is thus probable that gp85-regions defined by peptides 11435, 11436, and 11438 are involved in EBV invasion of B-lymphocytes.

Pathogenic roles for Epstein-Barr virus (EBV) gene products in EBV-associated proliferative disorders

Epstein-Barr virus (EBV) is associated with a still growing spectrum of clinical disorders, ranging from acute and chronic inflammatory diseases to lymphoid and epithelial malignancies. Based on a combination of in vitro and in vivo findings, EBV is thought to contribute in the pathogenesis of these diseases. The different EBV gene expression patterns in the various disorders, suggest different EBV-mediated pathogenic mechanisms. In the following pages, an overview of the biology of EBV-infection is given and functional aspects of EBV-proteins are discussed and their putative role in the various EBV-associated disorders is described. EBV gene expression patterns and possible pathogenic mechanisms are discussed. In addition, expression of the cellular genes upregulated by EBV in vitro is discussed, and a comparison with the in vivo situation is made.

CR2/CD21 proximal promoter activity is critically dependent on a cell type-specific repressor

Transcription of the human complement receptor type 2 (CR2/CD21) gene is controlled by both proximal promoter and intronic elements. CR2 is primarily expressed on B cells from the immature through mature cell stages. We have previously described the presence of an intronic element that is required for both cell- and stage-specific expression of CR2. In this study, we report the identification of a cell type-specific repressor element within the proximal promoter. This repressor sequence is shown by linker scanning mutagenesis to comprise an E box motif. By supershift analysis this element binds members of the basic helix-loop-helix family of proteins, in particular E2A gene products. Mutational analysis demonstrates that binding of E2A proteins is critical for functioning of this repressor. Thus, E2A activity is key not only for early B cell development, but also for controlling CR2 expression, a gene expressed only during later stages of ontogeny.

Generation of recombinant human C3dg tetramers for the analysis of CD21 binding and function

CD21 (complement receptor 2, CR2) binds the terminal proteolytic fragments of the third component of complement (C3) that have been covalently attached to immune complexes or other targets during the activation of complement. We used the technique of in vivo biotinylation to create a recombinant multivalent ligand for CD21. A sequence coding for a biotinylation signal peptide was added to the 3' end of the human C3dg cDNA. The modified C3dg was expressed in Escherichia coli and biotinylated intracellularly by the bacterial biotin holoenzyme synthetase (BirA) enzyme. Monomeric C3dg was unable to bind to CD21 as determined by flow cytometry, while biotinylated recombinant C3dg (rC3dg) complexed with fluorochrome-conjugated streptavidin bound tightly. Binding was observed using CD21 positive B cells but not seen on pre-B cells that do not express this complement receptor. Two assays were used to assess the functional capacity of the recombinant C3dg. First, multimeric C3dg caused the phosphorylation of the mitogen-activated kinase, p38, in mature B lymphoma cells. Second, C3dg greatly enhanced the activation of primary B cells in combination with a sub-stimulatory concentration of anti-IgM monoclonal antibody. These results illustrate the utility of the technique of in vivo biotinylation to generate ligands for cell surface receptors that require multimerization for high avidity binding and function.

Growth transformation of primary epithelial cells with a NPC-derived Epstein-Barr virus strain

The Epstein-Barr virus (EBV) is associated with two major human epithelial malignancies, where it is likely to play a role in the malignant phenotype: undifferentiated nasopharyngeal carcinoma (100% of cases) and gastric carcinomas (about 10% of cases). We and others have obtained growth transformation of monkey kidney primary epithelial cells by transfection of viral DNA, especially with the BARF1 gene of EBV (Wei et al., 1997). We now report that the same type of primary epithelial cells can be growth-transformed using EBV particles derived from a nasopharyngeal carcinoma tumor line. Not only can these EBV-infected cells grow over 100 passages, escaping senescence, in contrast to their noninfected counterparts, but they can also survive and proliferate at very low cell density. Several subclones were characterized in terms of viral gene expression. All these clones gave a similar pattern, with detection of EBNA1 and BARF1 proteins but absence of LMP1. CD21, which is the main EBV receptor on B lymphocytes, was not expressed on parental monkey kidney epithelial cells nor on EBV-infected cell clones. This model of epithelial cell transformation will be useful for a better investigation of EBV functions critical for oncogenesis of epithelial cells.

Epstein-Barr virus infection and human malignancies

The Epstein-Barr virus (EBV) is a herpes virus which establishes a life-long persistent infection in over 90% of the human adult population world-wide. Based on its association with a variety of lymphoid and epithelial malignancies, EBV has been classified as a group 1 carcinogen by the International Agency for Research on Cancer. In this article we discuss the evidence supporting an aetiological role for EBV in the pathogenesis of human tumours. The biology of EBV infection will be described with special emphasis on viral transforming gene products. A brief survey of EBV-associated tumours is followed by a discussion of specific problems. Evidence is presented which suggests that failures of the EBV-specific immunity may play a role in the pathogenesis of EBV-associated tumours also in patients without clinically manifest immunodeficiencies. Finally, the timing of EBV infection in the pathogenesis of virus-associated malignancies is discussed. There is good evidence that EBV infection precedes expansion of the malignant cell populations in some virus-associated tumours. However, this is clearly not always the case and for some of these tumours there are indications that clonal genetic alterations may occur prior to EBV infection. Thus, whilst there is good evidence to suggest that EBV is a human carcinogen, its precise role(s) in the development of virus-associated human tumours requires clarification.

Epstein-Barr virus infection and human malignancies

The Epstein-Barr virus (EBV) is a herpes virus which establishes a life-long persistent infection in over 90% of the human adult population world-wide. Based on its association with a variety of lymphoid and epithelial malignancies, EBV has been classified as a group 1 carcinogen by the International Agency for Research on Cancer. In this article we discuss the evidence supporting an aetiological role for EBV in the pathogenesis of human tumours. The biology of EBV infection will be described with special emphasis on viral transforming gene products. A brief survey of EBV-associated tumours is followed by a discussion of specific problems. Evidence is presented which suggests that failures of the EBV-specific immunity may play a role in the pathogenesis of EBV-associated tumours also in patients without clinically manifest immunodeficiencies. Finally, the timing of EBV infection in the pathogenesis of virus-associated malignancies is discussed. There is good evidence that EBV infection precedes expansion of the malignant cell populations in some virus-associated tumours. However, this is clearly not always the case and for some of these tumours there are indications that clonal genetic alterations may occur prior to EBV infection. Thus, whilst there is good evidence to suggest that EBV is a human carcinogen, its precise role(s) in the development of virus-associated human tumours requires clarification.

Epstein-Barr virus infection and human malignancies

The Epstein-Barr virus (EBV) is a herpes virus which establishes a life-long persistent infection in over 90% of the human adult population world-wide. Based on its association with a variety of lymphoid and epithelial malignancies, EBV has been classified as a group 1 carcinogen by the International Agency for Research on Cancer. In this article we discuss the evidence supporting an aetiological role for EBV in the pathogenesis of human tumours. The biology of EBV infection will be described with special emphasis on viral transforming gene products. A brief survey of EBV-associated tumours is followed by a discussion of specific problems. Evidence is presented which suggests that failures of the EBV-specific immunity may play a role in the pathogenesis of EBV-associated tumours also in patients without clinically manifest immunodeficiencies. Finally, the timing of EBV infection in the pathogenesis of virus-associated malignancies is discussed. There is good evidence that EBV infection precedes expansion of the malignant cell populations in some virus-associated tumours. However, this is clearly not always the case and for some of these tumours there are indications that clonal genetic alterations may occur prior to EBV infection. Thus, whilst there is good evidence to suggest that EBV is a human carcinogen, its precise role(s) in the development of virus-associated human tumours requires clarification.

Regulation of CD21 expression by DNA methylation and histone deacetylation

The complement receptor II (CD21) serves as a receptor for the complement component C3d of immune complexes on B lymphocytes. Expression of the CD21 gene is tightly regulated during B lymphocyte differentiation. Only mature B lymphocytes, but not pro-, pre- or plasma B lymphocytes, express CD21. There is evidence that cell type-specific expression is mediated by a silencer element located in the first intron. The CD21 promoter region contains a CpG island adjacent to the ATG start codon. We have analyzed the methylation status of this CpG island in B lymphoid cell lines representing the various differentiation stages of B lymphocyte development and primary lymphocytes. We found that the pro-, pre- and intermediate B lymphocytes contain a methylated CpG island and do not express CD21, whereas CD21-expressing mature B lymphocytes, plasma B lymphocytes and non-lymphoid cells carry a demethylated CD21 CpG island. To analyze whether the lack of CD21 expression in early B lymphocytes is due to inhibition by CpG methylation we have used 5-aza-2'-deoxycytidine to inhibit DNA methyltransferase activity. Treatment of pro-B lymphocytes with the drug resulted in expression of CD21. We have also applied Trichostatin A (TSA), an inhibitor of histone deacetylation, to determine whether the state of histone deacetylation affects the expression of CD21. We found that TSA induces expression of CD21 in early B lymphocytes. Thus CD21 expression is controlled by both methylation of the CD21 CpG island and chromatin modification through histone deacetylation in early B lymphocyte development.

Immunohistochemical absence of CD21 membrane receptor in nasopharyngeal carcinoma cells infected by Epstein-Barr virus in Spanish patients

OBJECTIVES/HYPOTHESIS

The aim of this study was to analyze the relevance of the CD21 membrane receptor in nasopharyngeal carcinoma (NPC). CD21 is implicated in the introduction of the Epstein-Barr virus (EBV) genome into epithelial cells and B lymphocytes.

STUDY DESIGN

Immunohistochemical analysis of CD21 in NPC.

METHODS

Paraffin-embedded samples of NPC of different histological types with demonstrated presence of EBV were analyzed for CD21 expression using immunohistochemistry.

RESULTS

We detected EBV by non-isotopic in situ hybridization (NISH) and nested polymerase chain reaction (PCR) in 100% of samples, regardless of histological type, supporting the previous view that all the types of NPC are variants of an EBV-associated malignancy. CD21 was not detected in NPC, and this absence was a typical feature in our data group.

CONCLUSIONS

The loss of the CD21 membrane receptor could be one of the immunophenotypical changes of the neoplastic cells that occur in the evolution of the NPC malignancy.

Epstein-Barr virus infection in the pathogenesis of nasopharyngeal carcinoma

The association of nasopharyngeal carcinoma (NPC) with the Epstein-Barr virus (EBV) was firmly established as early as 1973. Nevertheless, the role for the virus in the pathogenesis of NPC is still controversial. In this article, the evidence implicating EBV in the development of NPC is reviewed, focusing on the cellular site of EBV persistence, the association of the virus with different NPC histotypes, the tumour cell phenotype in the context of viral latent gene expression, and the possible role of the lymphoid stroma.

Coreceptor restriction within the HLA-DQ locus for Epstein-Barr virus infection

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus that causes infectious mononucleosis and is etiologically associated with malignancies of multiple origins. EBV enters cells through a cascade of interactions between its envelope glycoprotein gp350 and the gp42-gH-gL complex with cellular receptors. Membrane fusion is catalyzed by the binding of gp42, a member of the C type lectin family, to HLA class II molecule HLA-DR, -DP, or -DQ. Here we demonstrate that only a subset of HLA-DQ alleles mediates EBV entry, indicating that individuals expressing these alleles may offer unique sites for EBV infection and subsequent sequelae. Additionally, the specific site within HLA-DQ determined to be essential for EBV entry is homologous to a site within MHC class I shown by structural studies to bind to the C type-lectin-like natural killer receptor, providing insight into the biochemical nature of the gp42-HLA class II interaction.

Regulation of B lymphocyte responses to foreign and self-antigens by the CD19/CD21 complex

The membrane protein complex CD19/CD21 couples the innate immune recognition of microbial antigens by the complement system to the activation of B cells. CD21 binds the C3d fragment of activated C3 that becomes covalently attached to targets of complement activation, and CD19 co-stimulates signaling through the antigen receptor, membrane immunoglobulin. CD21 is also expressed by follicular dendritic cells and mediates the long-term retention of antigen that is required for the maintenance of memory B cells. Understanding of the biology of this receptor complex has been enriched by analyses of genetically modified mice; these analyses have uncovered roles not only in positive responses to foreign antigens, but also in the development of tolerance to self-antigens. Studies of signal transduction have begun to determine the basis for the coreceptor activities of CD19. The integration of innate and adaptive immune recognition at this molecular site on the B cell guides the appropriate selection of antigen by adaptive immunity and emphasizes the importance of this coreceptor complex.

Integrin expression in oral hairy leukoplakia and normal tongue epithelium

OBJECTIVE

To describe the expression of integrins in the epithelium of oral hairy leukoplakia (HL) and compare to that of normal lateral tongue epithelium.

MATERIALS AND METHODS

Immunohistochemistry to identify integrins (alpha 2, alpha 3, alpha 5, alpha 6, alpha v, beta 1) was performed, using a standard biotin-streptavidin-peroxidase technique on five clinically and histologically confirmed frozen biopsy specimens of HL and five normal lateral tongue control tissues.

RESULTS

Expression of integrins alpha 2, alpha 3, alpha 6, alpha v, beta 1 was seen both in HL epithelium and in normal control tissue. alpha 5 expression was not seen in HL or in control tissue epithelium. alpha 2 and alpha 3 were expressed mainly in the basal and suprabasal layers; alpha 6 expression was most intense on the basal surface of the basal cells, alpha v was expressed in the basal and suprabasal layers with more expression seen in the higher differentiated cell layers than the other integrins. beta 1 expression was seen in the basal and suprabasal layers only. No apparent difference between HL and normal oral mucosa was noted in the staining pattern of the various integrins.

CONCLUSION

Integrins alpha 2, alpha 3, alpha 6, alpha v, beta 1 are expressed in HL and the expression pattern is not different from that of normal oral mucosa. alpha 5 is not expressed in HL or in normal oral epithelium.

Epstein-Barr virus--positive undifferentiated thymic carcinoma in a 12-year-old white girl

Thymic epithelial malignant diseases are extremely rare in children. The authors report a 12-year-old white girl admitted for a polymetastatic tumor of the anterior mediastinum. Tumor proliferation was typical of an undifferentiated thymic carcinoma. A close link between Epstein-Barr virus (EBV) and the tumor was established by a high titer of anti-VCA IgA and the presence of EBV RNA and DNA in the tumor. In addition, monoclonal viral episomes were present in tumor cells, indicating that EBV infection was an early event in the oncogenic process. The patient died despite resection, irradiation, and chemotherapy.

Patterned entry and egress by Epstein-Barr virus in polarized CR2-positive epithelial cells

In polarized epithelium direction of viral entry and release correlates with proclivity of a virus to establish local versus systemic infection. The Epstein-Barr virus (EBV), whose principal tissue reservoir is B lymphocytes, also has disease manifestations in epithelium, suggesting intertissue spread potentially influenced by epithelial cell polarity. We stably transfected the B lymphocyte EBV receptor (CR2/CD21) into Madin-Darby canine kidney (MDCK) epithelial cells used extensively to study effects of cell polarity on infection by both DNA and RNA viruses. CR2/CD21 was detected on both apical and basolateral surfaces of polarized MDCK cells, with predominant expression basolaterally. However, infectivity was up to four-fold greater apically, suggesting that endogenous cell surface molecules, sorted asymmetrically onto polarized plasma membranes, may be involved in EBV entry into MDCK cells. EBV gp350/220, a replicative cycle glycoprotein added to the virus envelope on egress through the cell membrane, was immunolocalized by confocal microscopy to basolateral cell surfaces only. Apical entry of EBV with subsequent basolateral release of newly replicated virus favors systemic infection by viral dissemination to underlying lymphocytic aggregations. Under conditions of long-term culture, latent EBV was not stably maintained in these cells, suggesting that the epithelial phase of acute EBV infection may be transient.

Epstein-Barr virus infection of renal proximal tubule cells: possible role in chronic interstitial nephritis

Chronic interstitial nephritis frequently accompanies renal diseases of different etiologies. Far less common is the entity of primary interstitial nephritis wherein the glomerular and vascular structures of the kidney are not the primary focus of the disease process. Using in situ hybridization and the polymerase chain reaction, we detected DNA from the Epstein-Barr Virus (EBV) exclusively in renal tissue of patients with the idiopathic variety of chronic interstitial nephritis. The EBV genome, but not that of cytomegalovirus or adenovirus, was detected primarily in renal proximal tubule cells. Furthermore, the CD21 antigen, which serves as the receptor for EBV in B lymphocytes, was detected by immunocytochemistry primarily on proximal tubule cells and was markedly upregulated in the EBV-infected tissue. Western blot analysis of primary cultures of normal proximal tubule cells identified a 140-kDa protein, confirming the expression of the CD21 antigen. Colocalization experiments using proximal and distal tubule markers confirmed that EBV DNA and the CD21 antigen are found primarily in proximal tubule cells. EBV infection of renal proximal tubular cells may participate in evoking a cellular immune response that results in a damaged renal interstitium.

Epstein-Barr virus envelope glycoprotein gp350 induces NF-kappaB activation and IL-1beta synthesis in human monocytes-macrophages involving PKC and PI3-K

Epstein-Barr virus (EBV) is a highly immunotropic human herpesvirus with oncogenic potential and is involved in numerous pathologies. EBV utilizes its major envelope glycoprotein gp350 to bind to its receptor CR2/CD21 on target cells for initiating the infection. We have previously shown that EBV is able to modulate transcription and translation of a number of cytokine genes via its gp350-mediated binding to this receptor. However, the effects of the binding of purified gp350 to CR2/CD21 on plastic-adherent monocyte-macrophages (AMM) have not been investigated. These cells are a rich source of potent proinflammatory and immune-modulating cytokines, and express low levels of CR2/CD21. We show here for the first time that recombinant gp350 (rgp350) causes production of the potent proinflammatory cytokine IL-1beta in human AMM. Surprisingly, rgp350 is comparable in this capacity to the phorbol ester 12-0-tetradecanoylphorbol 13-acetate. This induction of IL-1beta production was accompanied by increased steady-state levels of its mRNA in gp350-treated AMM, and was dependent on the specific binding of rgp350 to the EBV receptor CR2/CD21. We also show that the signaling pathways resulting in the induction of IL-1beta synthesis by rgp350 required protein kinase C and phosphatidylinositol 3,4,5 triphosphate kinase activities and occurred via activation of the NF-kappaB family of transcription factors.-D'Addario, M., Ahmad, A., Xu, J. W., Menezes, J. Epstein-Barr virus envelope glycoprotein gp350 induces NF-kappaB activation and IL-1beta synthesis in human monocytes-macrophages involving PKC and PI3-K.

Epstein-Barr Virus Induces Fas (CD95) in T Cells and Fas Ligand in B Cells Leading to T-Cell Apoptosis

Epstein-Barr virus (EBV) acute infectious mononucleosis (AIM) is characterized by transient immunosuppression in vivo and increased T-cell apoptosis after ex vivo culture of AIM peripheral blood mononuclear cells. We undertook experiments to test whether EBV or purified virion envelope glycoprotein gp350 could contribute to Fas-mediated T-cell apoptosis. Our in vitro results indicate that EBV increased Fas expression in CD4+ T cells and Fas ligand (FasL) expression in B cells and macrophages. Purified gp350 was also shown to significantly increase CD95 expression in CD4+ T cells. When T-cell CD95 was cross-linked, EBV-stimulated T cells underwent apoptosis. The induction of T-cell CD95 by EBV followed by CD95 cross-linking with anti-CD95 monoclonal antibody resulted in a loss in the number of T cells responding to the T-cell mitogens, anti-CD3 antibody, and interleukin-2. These results indicate that, in addition to serving as a principal ligand for the attachment of virus to target cells, gp350 may also act as an immunomodulatory molecule that promotes T-cell apoptosis.

Possible involvement of IL-12 expression by Epstein-Barr virus in Sjögren syndrome

AIM

To determine the correlation between interleukin 12 (IL-12) expression and Epstein-Barr virus (EBV) in Sjögren syndrome.

METHODS

Indirect immunohistochemical technique, enzyme linked immunosorbent assay (ELISA), and immunoblot analysis were used to investigate IL-12 expression by EBV activation, using 13 surgical specimens and four B cell lines.

RESULTS

Marked expression of IL-12 was found in the epithelial cells and the infiltrating B cells of salivary gland tissues from patients with Sjögren syndrome (six of 10 cases), but not in those from normal individuals (none of three cases). A striking topographic correlation between IL-12 and EBV was found. In addition, levels of IL-12 production by B cell lines were clearly enhanced by EBV activation in vitro.

CONCLUSIONS

IL-12 expression closely reflects the intracellular event of EBV activation in Sjögren syndrome, and may contribute to the T helper cell type 1 (Th1) cytokine overexpression seen in this disease.

Requirement for cell-to-cell contact in Epstein-Barr virus infection of nasopharyngeal carcinoma cells and keratinocytes

Two nasopharyngeal carcinoma (NPC) cell lines and one keratinocyte cell line could be infected with Epstein-Barr virus (EBV) by cocultivation with virus-producing cells but not by cell-free virus. Using porous culture inserts to manipulate the cell-to-cell contact, we demonstrated that contact between EBV donor B cells and EBV recipient epithelial cells was required for the infection. Cell-to-cell contact not only provided a CR2-independent route of infection but also enhanced CR2-mediated infection in a synergistic manner. Activity of two EBV promoters (Cp and Wp) and expression of EBNA2 were detected in the infected population. A small proportion of the infected cells spontaneously entered an EBV lytic state, which could be induced prominently by chemical treatment. This study provides information on how EBV may infect epithelial cells in vivo, such as at the onset of NPC development.

Analysis of Epstein-Barr virus (EBV) receptor CD21 on peripheral B lymphocytes of long-term EBV- adults

Primary infections with EBV are rarely observed after the age of 20. Some individuals even remain seronegative all their lives. Previously, a lack of EBV receptors on B cells of persistently EBV- adults was described as a reason for long-term EBV-seronegativity. The present study examined the CD21 receptor status of 20 repeatedly EBV- healthy adults and 32 EBV+ volunteers by means of flow cytometry. CD21 molecules on the surface of CD19+ B cells were quantified using anti-IgG-coated microbeads. The percentage of CD19+/CD21+ B lymphocytes was slightly lower in the peripheral blood of EBV- donors, but the CD21 antibody binding capacity on CD19+ B cells showed no significant differences between EBV- and EBV+ adults. In vitro studies showed an equally good EBV transformability of peripheral B lymphocytes of EBV- and EBV+ donors. Since HLA-DR was recently described as a co-receptor for EBV infection of B cells, we also determined HLA-DRB1 alleles in the EBV- group. We found a significant negative association of EBV-seronegativity with HLA-DR13 in comparison with 111 healthy blood donors. In summary, a biologically significant lack of the EBV receptor CD21 on peripheral B lymphocytes of persistently EBV- adults was excluded as a reason for long-term EBV-seronegativity.

CD21-Dependent infection of an epithelial cell line, 293, by Epstein-Barr virus

Epstein-Barr virus (EBV) is invariably present in undifferentiated nasopharyngeal carcinomas, is found sporadically in other carcinomas, and replicates in the differentiated layer of the tongue epithelium in lesions of oral hairy leukoplakia. However, it is not clear how frequently or by what mechanism EBV infects epithelial cells normally. Here, we report that a human epithelial cell line, 293, can be stably infected by EBV that has been genetically marked with a selectable gene. We show that 293 cells express a relatively low level of CD21, that binding of fluorescein-labeled EBV to 293 cells can be detected, and that both the binding of virus to cells and infection can be blocked with antibodies specific for CD21. Two proteins known to form complexes with CD21 on the surface of lymphoid cells, CD35 and CD19, could not be detected at the surface of 293 cells. All infected clones of 293 cells exhibited tight latency with a pattern of gene expression similar to that of type II latency, but productive EBV replication and release of infectious virus could be induced inefficiently by forced expression of the lytic transactivators, R and Z. Low levels of mRNA specific for the transforming membrane protein of EBV, LMP-1, as well as for LMP-2, were detected; however, LMP-1 protein was either undetectable or near the limit of detection at less than 5% of the level typical of EBV-transformed B cells. A slight increase in expression of the receptor for epidermal growth factor, which can be induced in epithelial cells by LMP-1, was detected at the cell surface with two EBV-infected 293 cell clones. These results show that low levels of surface CD21 can support infection of an epithelial cell line by EBV. The results also raise the possibility that in a normal infection of epithelial cells by EBV, the LMP-1 protein is not expressed at levels that are high enough to be oncogenic and that there might be differences in the cells of EBV-associated epithelial cancers that have arisen to allow for elevated expression of LMP-1.

Transcription of Epstein-Barr virus latent cycle genes in oral hairy leukoplakia

The hairy leukoplakia lesion (HLP) is a unique example of a permissive infection with Epstein-Barr virus (EBV) in the tongue epithelium. HLP contains abundant replicating viral DNA and may be coinfected with multiple EBV strains. In this study, characterization of viral gene transcription within HLP biopsy specimens revealed that several genes, usually expressed in latently infected lymphocytes, are also transcribed in the HLP lesion. The BamHI W and C promoters, (Wp and Cp) are consistently active in the HLP lesion, resulting in transcription and processing of mRNAs that encode the Epstein-Barr nuclear antigens (EBNAs) EBNA-LP, EBNA1, EBNA2, EBNA3B, and EBNA3C. The EBNA2 protein has been shown to activate expression of the EBV receptor, CD21. In HLP, CD21 transcription is also detected, usually in samples that contain transcripts for EBNA2. Transcripts encoding the LMP1 gene, the LMP2 gene, and rightward transcripts from the BamHI A fragment of the EBV genome are also detected in HLP. These gene products are invariably expressed in latently infected lymphocytes. This pattern of transcription suggests that genes characteristic of latent infection are also expressed in HLP. The activation of Wp and expression of EBNA2 and CD21 may contribute to the unique ability of the HLP lesion to permit superinfection and viral replication of multiple EBV strains.

Comparative analysis of Epstein-Barr virus (EBV) detection by nested-PCR and non-isotopic in situ hybridization in nasopharyngeal carcinoma (NPC)

The aims of this study were two-fold: first, to assess the relative diagnostic performance of non-isotopic in situ hybridization (ISH) and the nested polymerase chain reaction (nested-PCR) applied to Epstein-Barr virus (EBV) detection in a series of 55 unselected nasopharyngeal carcinoma (NPC) cases and, secondly, to correlate these data with histopathological classification. Our study shows that in 76.36% of NPC cases positive nuclear signals were observed using EBV-ISH. Overall, EBV-ISH positivity varied according to histological type, in that undifferentiated carcinomas showed a higher proportion of positive cases than differentiated cell carcinomas, although ISH results do not show significant differences in relation to histological types when employing two different schemes (WHO and Micheau). However, in adequate quality DNA samples (54 NPC cases), EBV-DNA was detected in 100% of cases using a nested-PCR, supporting the previous view that all histological types of NPC are in reality variants of EBV-infected neoplasia. ISH-negative cases probably reflect a lower sensitivity than PCR, particularly when a small number of viral copies are present, as well as a variable technical effectiveness for detected EBV, independent of the NPC histological type.

An Intronic Silencer Regulates B Lymphocyte Cell- and Stage-Specific Expression of the Human Complement Receptor Type 2 (CR2, CD21) Gene

Human CR2 (CD21) is a B lymphocyte protein whose surface expression is restricted primarily to the mature cell stage during development. To study the transcriptional mechanisms that govern cell- and stage-restricted CR2 expression, we first performed transient transfection analysis using constructs extending from −5 kb to +75 bp (−5 kb/+75) in the CR2 promoter. The promoter was found to be broadly active, with no evidence of cell- or stage-specific reporter gene expression. However, the addition of a 2.5-kb intronic gene segment (containing a DNase I hypersensitive site) to the (−5-kb/+75) construct resulted in appropriate reporter gene expression, defined as the silencing of the (−5-kb/+75) promoter activity only in non-CR2-expressing cells. Interestingly, appropriate reporter gene expression required stable transfection of the constructs in cell lines, suggesting nuclear matrix or chromatin interactions may be important for appropriate CR2 gene expression. Importantly, transgenic mice also required the intronic silencer to generate lymphoid tissue-specific reporter gene expression. Some transgenic founder lines did not demonstrate reporter gene expression, however, indicating that additional transcriptional regulatory elements are present in other regions of the CR2 gene. In summary, these data support the hypothesis that human CR2 expression is regulated primarily by an intronic silencer with lineage- and B cell stage-specific activity.

Epstein-Barr virus infection of human gastric carcinoma cells: implication of the existence of a new virus receptor different from CD21

Recombinant Epstein-Barr virus (EBV) with a selectable marker successfully infected the human gastric carcinoma cell lines AGS, MKN28, and MKN74. Following incubation in selective media, drug-resistant cell clones were isolated and proved to be infected with EBV. All gastric carcinoma cell clones were positive for EBNA 1 but negative for EBNA 2. LMP 1 expression was negative in most clones, but there were a few exceptions. Gastric carcinoma cells were negative for the EBV receptor CD21, and infection was not inhibited by pretreatment of cells with the anti-CD21 monoclonal antibody OKB7. The results indicate that gastric carcinoma cells are susceptible to EBV infection and that infection is mediated via a new receptor different from CD21.

Characterization of C3 receptors on cultured rat glomerular endothelial cells

In this study we characterized C3 receptors on cultured rat glomerular endothelial cells (GEnC), using immunochemical and molecular techniques. GEnC membrane proteins were immunoprecipitated with a polyclonal antibody directed towards mouse complement receptor 2 (CR2). This anti-MCR2 immunoprecipitated GEnC proteins of 120 and 150 kDa. By immunohistochemistry, anti-MCR2 stained GEnC in rat glomeruli in vivo. Given the presence of CR2-like proteins on GEnC, subsequent studies were done to determine whether GEnC had C3-binding proteins. GEnC proteins of 80, 200, and 300 kDa specifically bound to columns of rat C3d-Sepharose and C3b-Sepharose, illustrating that these proteins were binding to the C3d portion of C3. The 80, 200, and 300 kDa C3d-binding proteins were distinct from the 120 and 150 kDa anti-MCR2 reactive proteins, as shown by immunoabsorption studies. Next, a specific cDNA probe for rat CR2 was generated by RT-PCR. Oligonucleotides were chosen from highly conserved regions in mouse and human CR2 spanning 224 bases, with the rationale that these would also be conserved in the rat. A 224 bp PCR product was generated from both rat GEnC and rat kidney cDNA, illustrating the presence of CR2 mRNA in these tissues. By Northern analysis, the CR2 PCR product hybridized to mRNA of 2 and 5 kb from GEnC. The 5 kb transcript was also identified in rat kidney mRNA. Therefore, proteins immunologically related to mouse CR2 are present in GEnC in vitro and in vivo. C3d-binding proteins of 80, 200, and 300 kDa are also present on rat GEnC, yet these appear to be immunologically distinct from the proteins identified by anti-MCR2. Whether the GEnC CR2 mRNA transcripts of 2 and 5 kb are translated into the 80 and 200 kDa C3d-binding proteins or the 120 and 150 kDa mouse CR2-like proteins remains to be defined.

Epstein-Barr virus permissively infects human syncytiotrophoblasts in vitro and induces replication of human T cell leukemia-lymphoma virus type I in dually infected cells

Epstein-Barr virus (EBV) and human immunodeficiency virus type 1 (HIV-1), as well as human T-cell leukemia-lymphoma virus type I (HTLV-I), may interact in the pathogenesis of human retroviral infections. The placental syncytiotrophoblast layer represents a barrier protecting the fetal compartment from exposure to retroviruses. We studied the interactions of EBV with HIV-1 and HTLV-I in human term syncytiotrophoblast cells to investigate the significance of double infections in transplacental transmission of human retroviruses. We found that syncytiotrophoblast cells could be productively infected with EBV. Dual infection of the cells with EBV and HTLV-I resulted in full replication cycle of otherwise latent HTLV-I. In contrast, the restricted permissiveness of syncytiotrophoblasts for HIV-1 was not influenced by coinfection of the cells with EBV. Infection of syncytiotrophoblast cells with EBV, but not HTLV-I, induced interleukin-2 and interleukin-6 secretion, and augmented secretion occurred on coinfection with both viruses. Coinfection of syncytiotrophoblast cells with EBV and HTLV-I induced tumor necrosis factor-beta and transforming growth factor-beta 1 secretion, but infection with either virus alone did not lead to secretion of these cytokines. Permissive replication cycle of HTLV-I was induced by the EBV immediate-early gene product Zta. Pseudotype formation between EBV and HTLV-I in coinfected syncytiotrophoblast cells was not found. Our data suggest that activation of HTLV-I gene expression by EBV in coinfected syncytiotrophoblast cells may be a mechanism for transplacental transmission of HTLV-I.