Epstein-Barr viruses that express a CD21 antibody provide evidence that gp350's functions extend beyond B-cell surface binding

Shared and distinct interactions of type 1 and type 2 Epstein-Barr Nuclear Antigen 2 with the human genome

BACKGROUND

There are two major genetic types of Epstein-Barr Virus (EBV): type 1 (EBV-1) and type 2 (EBV-2). EBV functions by manipulating gene expression in host B cells, using virus-encoded gene regulatory proteins including Epstein-Barr Nuclear Antigen 2 (EBNA2). While type 1 EBNA2 is known to interact with human transcription factors (hTFs) such as RBPJ, EBF1, and SPI1 (PU.1), type 2 EBNA2 shares only ~ 50% amino acid identity with type 1 and thus may have distinct binding partners, human genome binding locations, and functions.

RESULTS

In this study, we examined genome-wide EBNA2 binding in EBV-1 and EBV-2 transformed human B cells to identify shared and unique EBNA2 interactions with the human genome, revealing thousands of type-specific EBNA2 ChIP-seq peaks. Computational predictions based on hTF motifs and subsequent ChIP-seq experiments revealed that both type 1 and 2 EBNA2 co-occupy the genome with SPI1 and AP-1 (BATF and JUNB) hTFs. However, type 1 EBNA2 showed preferential co-occupancy with EBF1, and type 2 EBNA2 preferred RBPJ. These differences in hTF co-occupancy revealed possible mechanisms underlying type-specific gene expression of known EBNA2 human target genes: MYC (shared), CXCR7 (type 1 specific), and CD21 (type 2 specific). Both type 1 and 2 EBNA2 binding events were enriched at systemic lupus erythematosus (SLE) and multiple sclerosis (MS) risk loci, while primary biliary cholangitis (PBC) risk loci were specifically enriched for type 2 peaks.

CONCLUSIONS

This study reveals extensive type-specific EBNA2 interactions with the human genome, possible differences in EBNA2 interaction partners, and a possible new role for type 2 EBNA2 in autoimmune disorders. Our results highlight the importance of considering EBV type in the control of human gene expression and disease-related investigations.

Immunity and Immune Evasion Mechanisms of Epstein-Barr Virus

Epstein-Barr virus (EBV) is the first human oncogenic virus to be identified, which evades the body's immune surveillance through multiple mechanisms that allow long-term latent infection. Under certain pathological conditions, EBVs undergo a transition from the latent phase to the lytic phase and cause targeted dysregulation of the host immune system, leading to the development of EBV-related diseases. Therefore, an in-depth understanding of the mechanism of developing an immune response to EBV and the evasion of immune recognition by EBV is important for the understanding of the pathogenesis of EBV, which is of great significance for finding strategies to prevent EBV infection, and developing a therapy to treat EBV-associated diseases. In this review, we will discuss the molecular mechanisms of host immunological responses to EBV infection and the mechanisms of EBV-mediated immune evasion during chronic active infection.

Contribution of carbohydrate-related metabolism in Herpesvirus infections

Human herpesviruses are enveloped viruses with double-stranded linear DNA genomes highly prevalent in the human population. These viruses are subdivided into three subfamilies, namely alphaherpesvirinae (herpes simplex virus type 1, HSV-1; herpes simplex virus type 2, HSV-2; and varicella-zoster virus, VZV), betaherpesvirinae (human cytomegalovirus, HCMV; human herpesvirus 6, HHV-6; and human herpesvirus 7, HHV-7) and gammaherpesvirinae (Epstein-Barr virus, EBV; and Kaposi's sarcoma-associated herpesvirus, KSHV). Besides encoding numerous molecular determinants to evade the host antiviral responses, these viruses also modulate cellular metabolic processes to promote their replication. Here, we review and discuss existing studies describing an interplay between carbohydrate metabolism and the replication cycle of herpesviruses, altogether highlighting potentially new molecular targets based on these interactions that could be used to block herpesvirus infections.

AbSE Workflow: Rapid Identification of the Coding Sequence and Linear Epitope of the Monoclonal Antibody at the Single-cell Level

Monoclonal antibody (mAb) has been widely used in immunity research and disease diagnosis and therapy. Antibody sequence and epitope are the prerequisites and basis of mAb applications, which determine the properties of antibodies and make the preparation of antibody-based molecules controllable and reliable. Here, we present the antibody sequence and epitope identification (AbSE) workflow, a time-saving and cost-effective route for rapid determination of antibody sequence and linear epitope of mAb even at the single-cell level. The feasibility and accuracy of the AbSE workflow were demonstrated through the identification and validation of the coding sequence and epitope of antihuman serum albumin (antiHSA) mAb. It can be inferred that the AbSE workflow is a powerful and universal approach for paired antibody-epitope sequence identification. It may characterize antibodies not only on a single hybridoma cell but also on any other antibody-secreting cells.

Expression and Function of Tetraspanins and Their Interacting Partners in B Cells

Tetraspanins are transmembrane proteins that modulate multiple diverse biological processes, including signal transduction, cell–cell communication, immunoregulation, tumorigenesis, cell adhesion, migration, and growth and differentiation. Here, we provide a systematic review of the involvement of tetraspanins and their partners in the regulation and function of B cells, including mechanisms associated with antigen presentation, antibody production, cytokine secretion, co-stimulator expression, and immunosuppression. Finally, we direct our focus to the signaling mechanisms, evolutionary conservation aspects, expression, and potential therapeutic strategies that could be based on tetraspanins and their interacting partners.

Epstein-Barr virus infection and type I interferon signature in patients with systemic lupus erythematosus

Epstein-Barr (EB) virus infection has long been speculated to evoke systemic lupus erythematosus (SLE). Since a virus infection can induce interferon (IFN) system activation, we aimed to discover the relationship between the two in the progression of SLE in a Chinese inpatient cohort. Methods Peripheral blood mononuclear cells and sera were isolated from 116 SLE patients and 76 healthy controls. Antibodies against EBV-VCA (IgM and IgG) and EBNA (IgG) along with IFNα in patient sera were detected with enzyme-linked immunosorbent assays. The EB virus DNA load was detected by real-time quantitative polymerase chain reaction. Peripheral blood mononuclear cells both from patients and controls were isolated immediately. The mRNA from these samples was subjected to real-time PCR for the latent genes EBNA1, EBNA2 and LMP1 of EB virus, as well as four IFN-stimulated genes (ISGs) ( OASL, MX1, ISG15 and LY6E). The antibody results were used to determine the stage of EBV infection (lytic, latent, or previous). Results SLE patients had a higher rate of lytic infection defined as positive EBV-VCA IgM antibody (39.66% vs 10.53%, p = 0.027), but not the EB virus DNA load. Patients with lytic EB virus infection had higher SLEDAI scores than patients with non-lytic infection (15.24 ± 2.63 vs 13.79 ± 3.24, p = 0.012). LMP1 was the only EBV gene that had a higher expression level in SLE patients than in healthy controls (3.26 ± 2.95 vs 1.00 ± 2.89, p = 0.000). It was also positively correlated with SLEDAI scores ( r = 0.462, p = 0.000). Levels of IFNα and the four ISGs were all significantly higher in SLE patients than in healthy controls ( p < 0.05). LMP1 was positively correlated with the four ISGs ( r = 0.403 ∼ 0.494, p < 0.05) in SLE patients but not in healthy controls ( r = -0.153 ∼ 0.129, p > 0.05). Neither EBNA1 nor EBNA2 was correlated with the ISGs in SLE patients or in healthy controls. Conclusions The SLE patients had higher rates of lytic EB virus infection and higher latent gene LMP1 expression, which might be associated with the development and/or the progression of SLE via the type I IFN pathway. The underlying mechanism needs more study.

Using a Commonly Down-Regulated Cytomegalovirus (CMV) Promoter for High-Level Expression of Ectopic Gene in a Human B Lymphoma Cell Line

BACKGROUND Vectors are widely used to drive gene expression using a promoter. However, not all promoters are able to drive ectopic gene expression efficiently, including CMV promoter. Here, we report our data using CMV promoter for high-level gene expression in a B lymphoma cell line DG75. MATERIAL AND METHODS A plasmid (pcDNA3.1(+)) containing the CD21 gene driven under CMV promoter was constructed. The plasmid was stably transfected into a human B lymphoma cell line DG75 for cellular surface CD21 expression, and flow cytometry was used to monitor CD21 expression. CD21+ cells in the stable cell line were purified using anti-CD21 antibody-coupled Dynabeads for CD21-mediated antigen presentation experiment. RESULTS The percentage of CD21+ cells in newly generated stable DG75-pcDNA3.1(+)-CD21 cells was only 6.5% as determined by flow cytometry, which was unexpected and did not fit the requirements for further experiments. However, CD21+ cells could be purified to 100% using anti-CD21 antibody-coupled beads. The percentage of CD21+ cells in purified cells can be kept at 95%, 82%, 42%, 15%, and 42% at 7 d, 14 d, 34 d, and 42 d after purification, respectively. Specific T cell response against CD21-mediated antigen presentation can be activated successfully only when surface CD21 expression remains high. CONCLUSIONS A commonly down-regulated CMV promoter can be used to drive ectopic gene expression at a high-level in stable cell lines. Our results should facilitate future experimental design using other down-regulated promoters containing vectors such as SV40 and PGK1.

Human complement receptor type 1/CD35 is an Epstein-Barr Virus receptor

Epstein-Barr virus (EBV) attachment to primary B cells initiates virus entry. Although CD21 is the only known receptor for EBVgp350/220, a recent report documents EBV-infected B cells from a patient genetically deficient in CD21. On normal resting B cells, CD21 forms two membrane complexes: one with CD19 and another with CD35. Whereas the CD21/CD19 complex is widely retained on immortalized and B cell tumor lines, the related complement-regulatory protein CD35 is lost. To determine the role(s) of CD35 in initial infection, we transduced a CD21-negative pre-B cell and myeloid leukemia line with CD35, CD21, or both. Cells expressing CD35 alone bound gp350/220 and became latently infected when the fusion receptor HLA II was coexpressed. Temporal, biophysical, and structural characteristics of CD35-mediated infection were distinct from CD21. Identification of CD35 as an EBV receptor uncovers a salient role in primary infection, addresses unsettled questions of virus tropism, and underscores the importance of EBVgp350/220 for vaccine development.

An Epstein-Barr virus mutant produces immunogenic defective particles devoid of viral DNA

Virus-like particles (VLPs) from hepatitis B and human papillomaviruses have been successfully used as preventative vaccines against these infectious agents. These VLPs consist of a self-associating capsid polymer formed from a single structure protein and are devoid of viral DNA. Since virions from herpesviruses consist of a large number of molecules of viral and cellular origin, generating VLPs from a subset of these would be a particularly arduous task. Therefore, we have adopted an alternative strategy that consists of producing DNA-free defective virus particles in a cell line infected by a herpesvirus mutant incapable of packaging DNA. We previously reported that an Epstein-Barr virus (EBV) mutant devoid of the terminal repeats (ΔTR) that act as packaging signals in herpesviruses produces substantial amounts of VLPs and of light particles (LPs). However, ΔTR virions retained some infectious genomes, and although these mutants had lost their transforming abilities, this poses potential concerns for clinical applications. Therefore, we have constructed a series of mutants that lack proteins involved in maturation and assessed their ability to produce viral DNA-free VLP/LPs. Some of the introduced mutations were deleterious for capsid maturation and virus production. However, deletion of BFLF1/BFRF1A or of BBRF1 resulted in the production of DNA-free VLPs/LPs. The ΔBFLF1/BFRF1A viruses elicited a potent CD4(+) T-cell response that was indistinguishable from the one obtained with wild-type controls. In summary, the defective particles produced by the ΔBFLF1/BFRF1A mutant fulfill the criteria of efficacy and safety expected from a preventative vaccine.

EBV tegument protein BNRF1 disrupts DAXX-ATRX to activate viral early gene transcription

Productive infection by herpesviruses involve the disabling of host-cell intrinsic defenses by viral encoded tegument proteins. Epstein-Barr Virus (EBV) typically establishes a non-productive, latent infection and it remains unclear how it confronts the host-cell intrinsic defenses that restrict viral gene expression. Here, we show that the EBV major tegument protein BNRF1 targets host-cell intrinsic defense proteins and promotes viral early gene activation. Specifically, we demonstrate that BNRF1 interacts with the host nuclear protein Daxx at PML nuclear bodies (PML-NBs) and disrupts the formation of the Daxx-ATRX chromatin remodeling complex. We mapped the Daxx interaction domain on BNRF1, and show that this domain is important for supporting EBV primary infection. Through reverse transcription PCR and infection assays, we show that BNRF1 supports viral gene expression upon early infection, and that this function is dependent on the Daxx-interaction domain. Lastly, we show that knockdown of Daxx and ATRX induces reactivation of EBV from latently infected lymphoblastoid cell lines (LCLs), suggesting that Daxx and ATRX play a role in the regulation of viral chromatin. Taken together, our data demonstrate an important role of BNRF1 in supporting EBV early infection by interacting with Daxx and ATRX; and suggest that tegument disruption of PML-NB-associated antiviral resistances is a universal requirement for herpesvirus infection in the nucleus.

Epstein-Barr virus genetics: talking about the BAC generation

Genetic mutant organisms pervade all areas of Biology. Early on, herpesviruses (HV) were found to be amenable to genetic analysis using homologous recombination techniques in eukaryotic cells. More recently, HV genomes cloned onto a bacterial artificial chromosome (BAC) have become available. HV BACs can be easily modified in E.coli and reintroduced in eukaryotic cells to produce infectious viruses. Mutants derived from HV BACs have been used both to understand the functions of all types of genetic elements present on the virus genome, but also to generate mutants with potentially medically relevant properties such as preventative vaccines. Here we retrace the development of the BAC technology applied to the Epstein-Barr virus (EBV) and review the strategies available for the construction of mutants. We expand on the appropriate controls required for proper use of the EBV BACs, and on the technical hurdles researchers face in working with these recombinants. We then discuss how further technological developments might successfully overcome these difficulties. Finally, we catalog the EBV BAC mutants that are currently available and illustrate their contributions to the field using a few representative examples.