Epstein-Barr virus (EBV) antigens processed and presented by B cells, B blasts, and macrophages trigger T-cell-mediated inhibition of EBV-induced B-cell transformation

Gammaherpesviruses and B Cells: A Relationship That Lasts a Lifetime

Gammaherpesviruses are highly prevalent pathogens that establish life-long infection and are associated with diverse malignancies, including lymphoproliferative diseases and B cell lymphomas. Unlike other viruses that either do not infect B cells or infect B cells transiently, gammaherpesviruses manipulate physiological B cell differentiation to establish life-long infection in memory B cells. Disruption of such viral manipulation by genetic or environmental causes is likely to seed viral lymphomagenesis. In this review, we discuss physiological and unique host and viral mechanisms usurped by gammaherpesviruses to fine tune host B cell biology for optimal infection establishment and maintenance.

Epstein-Barr virus promotes human monocyte survival and maturation through a paracrine induction of IFN-alpha

The role of monocytes and macrophages during EBV infection is not clear. The interaction of EBV with human monocytes was investigated in terms of cell survival and morphological and phenotypic changes to gain a better understanding of the role of these cells during EBV infection. We show that EBV infection of PBMCs rescues monocytes from undergoing spontaneous apoptosis and dramatically enhances their survival. Results obtained with heat-inactivated virus, neutralizing anti-EBV mAb 72A1 and recombinant gp350, suggest that enhancement of viability by EBV requires both infectious virus and interaction between gp350 and its receptor. IFN-alpha either secreted within 24 h from PBMCs upon infection with EBV or exogenously added to unstimulated monocytes inhibited spontaneous apoptosis, indicating that induction of IFN-alpha is an early important survival signal responsible for the delay in the apoptosis of monocytes. EBV infection also induced acute maturation of monocytes to macrophages with morphological and phenotypic characteristics of potent APCs. Monocytes exposed to EBV became larger in size with increased granularity and expressed considerably higher levels of membrane HLA classes I and II, ICAM-1, CD80, CD86, and CD40 compared with uninfected cultures. These observations provide the first immunoregulatory links among EBV, IFN-alpha, and monocyte survival and maturation and importantly raise the possibility that these cells may serve as a vehicle for the dissemination of the virus as well as being active participants in eliciting anti-EBV T cell responses during acute infection.

The major Epstein-Barr virus (EBV) envelope glycoprotein gp340 when incorporated into Iscoms primes cytotoxic T-cell responses directed against EBV lymphoblastoid cell lines

A recombinant form of the EBV envelope glycoprotein and vaccine candidate gp340, lacking its hydrophobic transmembrane region, was incorporated into Iscoms after coupling to phosphatidyl ethanolamine via carbohydrate residues. Coupling by partial oxidation of gp340 carbohydrate with sodium periodate partly denatured the incorporated gp340 as indicated by its reduced reactivity with monoclonal antibodies that recognise the major neutralising epitope. Immunisation of cottontop tamarins with these Iscoms elicited antibody responses to gp340, but these antibodies only poorly recognised the major neutralising epitope in a competition ELISA and were unable to neutralise EBV in vitro. Despite the lack of neutralising antibody, immunisation with these Iscoms primed significant in vitro proliferative responses to soluble gp340 in lymphocytes from the draining lymph nodes and spleen. T-cell lines were raised from both immunised and control animals by in vitro stimulation of peripheral blood lymphocytes or spleen cells with autologous EBV-transformed lymphoblastoid cell lines. The T-cell lines from control animals had higher numbers of CD4+ T-cells than CD8+ T-cells and were not cytotoxic for autologous lymphoblastoid cell lines (LCL). In contrast the lines from immunised animals contained more CD8+ T-cells than CD4+ T-cells and had marked cytotoxicity for autologous LCL.

Epstein-Barr virus induces GM-CSF synthesis by monocytes: effect on EBV-induced IL-1 and IL-1 receptor antagonist production in neutrophils

Neutrophils play an important role in the control of viral infections by releasing a variety of potent agents. We previously demonstrated that Epstein-Barr virus (EBV) binds to human neutrophils and stimulates cytokine synthesis including interleukin-1 (IL-1) and IL-1 receptor antagonist (IL-1Ra). Since neutrophil functions are known to be modulated by the priming effect of granulocyte-macrophage colony-stimulating factor (GM-CSF), we therefore investigated the cellular source of GM-CSF synthesis following treatment of leukocytes with EBV and the effect of GM-CSF on the production of IL-1, IL-1Ra, and superoxide by EBV-treated neutrophils. In enriched-cell populations, only monocytes were found to produce GM-CSF in response to EBV, which was maximal after 12 h of incubation. The results obtained with UV-irradiated particles or EBV neutralized with monoclonal antibody 72A1 suggest that contact between the cell and the gp350 of the viral envelope is sufficient to induce the release of GM-CSF. On the other hand, GM-CSF differentially upregulated EBV-induced IL-1 and IL-1Ra production by neutrophils. Pretreatment of neutrophils with GM-CSF prior to EBV activation synergistically enhanced the production of IL-1 alpha and IL-1 beta, but only marginally affected IL-1Ra synthesis. In addition, GM-CSF was also found to synergistically enhance the superoxide production by neutrophils in response to EBV. Molecular analysis showed that GM-CSF did not alter the IL-1 beta and IL-1Ra mRNA synthesis induced by EBV, suggesting that GM-CSF could act at a posttranslational level. Local production of GM-CSF by monocytes in tissues invaded by EBV could serve to potentiate the host defense mechanisms directed toward the destruction of the infectious virus.

Epstein-Barr Virus Modulates 5-Lipoxygenase Product Synthesis in Human Peripheral Blood Mononuclear Cells

The effect of short-term coincubations of Epstein-Barr virus (EBV) with mononuclear cells on the synthesis of leukotrienes (LT) by monocytes was investigated. Although treatment of mononuclear cells with EBV alone had no significant effect on LT synthesis by monocytes, the preincubation of mononuclear cells with EBV before the further stimulation of the cells with either the ionophore A23187, the chemoattractant formyl-Met-Leu-Phe, or the phagocytic particles zymosan strikingly enhanced the formation of both LTB4 and LTC4 above the levels of synthesis observed with the stimuli alone. Such priming effect of EBV on LT synthesis was maximal after 15 minutes of preincubation of mononuclear cells with EBV and slowly declined at longer preincubation times; the priming effect of EBV was observed both in Hank's Balanced Salt Solution and plasma. The effect of EBV was abolished by prior treatment of viral particles by heat or by antibody raised against the glycoprotein gp350 of the viral envelope, but not by UV irradiation of the viral particles. Exposure of mononuclear cells to EBV was shown to strongly enhance the activation of the 5-lipoxygenase and the release of arachidonic acid induced upon cell stimulation with a second agonist. The release of arachidonic acid by the EBV-treated mononuclear cells was inhibitable by arachidonyl trifluoromethyl ketone, an inhibitor of the 80-kD cytosolic phospholipase A2 . Furthermore, EBV was shown to rapidly increase (maximum effect within 15 minutes) the levels of phosphorylated form of the cytosolic phospholipase A2 (as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis), a process related to the activation of this enzyme. These data show that the interaction of EBV with monocytes upregulates the formation of important lipid mediators of inflammation.

Immune regulation in Epstein-Barr virus-associated diseases

Epstein-Barr virus (EBV) is a member of the human herpesvirus family and, like many other herpesviruses, maintains a lifelong latent association with B lymphocytes and a permissive association with stratified epithelium in the oropharynx. Clinical manifestations of primary EBV infection range from acute infectious mononucleosis to an asymptomatic persistent infection. EBV is also associated with a number of malignancies in humans. This review discusses features of the biology of the virus, both in cell culture systems and in the natural host, before turning to the role of the immune system in controlling EBV infection in healthy individuals and in individuals with EBV-associated diseases. Cytotoxic T cells that recognize virally determined epitopes on infected cells make up the major effector arm and control the persistent infection. In contrast, the options for immune control of EBV-associated malignancies are more restricted. Not only is antigen expression restricted to a single nuclear antigen, EBNA1, but also these tumor cells are unable to process EBV latent antigens, presumably because of a transcriptional defect in antigen-processing genes (such as TAP1 and TAP2). The likelihood of producing a vaccine capable of controlling the acute viral infection and EBV-associated malignancies is also discussed.

Failure of Epstein-Barr virus-specific cytotoxic T lymphocytes to lyse B cells transformed with the B95-8 strain is mapped to an epitope that associates with the HLA-B8 antigen

There are two types, A and B, of Epstein-Barr virus (EBV) and B95-8 represents the common type A laboratory strain. Herein, we show in a family study that paternal EBV-specific cytotoxic T lymphocytes (CTL) generated in short-term cultures following stimulation with the autologous B95-8-transformed lymphoblastoid cell line (LCL) or B cells freshly infected with the B95-8 isolate did not lyse haploidentical B95-8 LCL expressing the HLA-A1, -B8, -DR3 paternal haplotype. In contrast, the haploidentical B95-8 LCL expressing the HLA-A11, -B51, -DR7 paternal haplotype was strongly lysed. Moreover, paternal CTL generated in response to stimulation with the B95-8 LCL expressing the haploidentical HLA-A1, -B8, -DR3 paternal haplotype included an allogeneic response against the maternal haplotype but no EBV-specific response as shown by the poor lysis of the autologous LCL target cells. However, stimulation with the haploidentical HLA-A11, -B51, -DR7 paternal haplotype resulted in the generation of both an allogeneic and an EBV-specific response. CTL clones were generated from two HLA-B8+ donors in response to stimulation with the autologous type A LCL transformed with wildtype EBV. The clones were cross-reactive for an immunodominant B95-8-associated peptide epitope that interacted with the HLA-B8 allele but failed to lyse B95-8-transformed LCL targets unless the targets were pre-coated with the exogenous peptide. A CTL clone that was initially stimulated with the autologous BL74 LCL lysed the spontaneous autologous LCL and spontaneous LCL from an HLA-B8+ donor, but failed to lyse the B95-8 LCL from that donor. The observed haplotype preference can be explained in terms of sequence variation between the B95-8 and the corresponding wildtype epitope. Our findings may help to clarify the role of EBV in the pathogenesis of primary Sjögren's syndrome which is closely associated with HLA-B8.

Altered HIV expression and EBV-induced transformation in coinfected PBLs and PBL subpopulations

Human immunodeficiency virus (HIV) IIIB expression and Epstein-Barr virus (EBV) B95.8-induced transformation were studied during coinfection. Coinfection of peripheral blood lymphocyte (PBL) cultures with HIV and EBV resulted in down-regulation of HIV expression. EBV-induced and spontaneous transformation were markedly reduced in PBL cultures exposed to HIV before EBV. On the other hand, transformation was enhanced when PBL cultures were infected with HIV either simultaneous to or after EBV. Reconstitution of EBV-infected B cell cultures with autochthonous T cells demonstrated that HIV-infected T cells had a reduced ability to inhibit EBV-induced transformation. PHA stimulation of HIV-infected T cells eliminated their ability to inhibit EBV-induced transformation. Lymphoblastoid cell lines (LCLs) established from coinfected PBLs expressed B cell markers and were EBV positive, while a large proportion of the LCLs expressed HIV antigens, released reverse transcriptase activity into the supernatant, and produced syncytia when cocultivated with indicator cell line SupT1. HIV provirus could be detected in LCLs established from coinfected cultures by PCR amplification using specific sets of amplimers for gag and env genes of HIV. To more closely examine the role of various cell types in lymphocyte transformation and HIV replication during coinfection, experiments were carried out using subpopulations enriched for either B or T cells. Simultaneous coinfection of purified B cells with EBV and HIV resulted in a marked reduction of HIV expression, whereas EBV-induced transformation was enhanced. In contrast, spontaneous B cell transformation was inhibited by HIV. A proportion of LCLs established from purified B cells coinfected with EBV and HIV expressed HIV antigens, released reverse transcriptase activity, and produced syncytia on SupT1 cells. These results demonstrate that the IIIB strain of HIV and B95.8 strain of EBV can interact during coinfection of B cells to alter the course of virus expression.