The Epstein-Barr virus determined nuclear antigen is composed of at least three different antigens

Epstein-Barr Virus-Specific Humoral Immune Responses in Health and Disease

Epstein-Barr virus (EBV) is widely distributed in the world and associated with a still increasing number of acute, chronic, malignant and autoimmune disease syndromes. Humoral immune responses to EBV have been studied for diagnostic, pathogenic and protective (vaccine) purposes. These studies use a range of methodologies, from cell-based immunofluorescence testing to antibody-diversity analysis using immunoblot and epitope analysis using recombinant or synthetic peptide-scanning. First, the individual EBV antigen complexes (VCA , MA, EA(D), EA(R) and EBNA) are defined at cellular and molecular levels, providing a historic overview. The characteristic antibody responses to these complexes in health and disease are described, and differences are highlighted by clinical examples. Options for EBV vaccination are briefly addressed. For a selected number of immunodominant proteins, in particular EBNA1, the interaction with human antibodies is further detailed at the epitope level, revealing interesting insights for structure, function and immunological aspects, not considered previously. Humoral immune responses against EBV-encoded tumour antigens LMP1, LMP2 and BARF1 are addressed, which provide novel options for targeted immunotherapy. Finally, some considerations on EBV-linked autoimmune diseases are given, and mechanisms of antigen mimicry are briefly discussed. Further analysis of humoral immune responses against EBV in health and disease in carefully selected patient cohorts will open new options for understanding pathogenesis of individual EBV-linked diseases and developing targeted diagnostic and therapeutic approaches.

EBNA2 and Notch signalling in Epstein-Barr virus mediated immortalization of B lymphocytes

Epstein-Barr virus (EBV) has the ability to immortalize B cells. A viral key protein for immortalization is the transactivator EBNA2 that controls expression of several viral and cellular genes. EBNA2 is tethered to promoters by interacting with the cellular repressor RBP-J. This resembles the physiological activation of RBP-J-repressed promoters by activated Notch receptors (Notch-IC). Since EBNA2 and Notch-IC have been shown to be partially interchangeable in regard to activation of target genes in B cell lines and modulation of differentiation processes it is conceivable that EBNA2 is a biological equivalent of an activated Notch receptor.

Molecular virology of Epstein-Barr virus

Epstein-Barr virus (EBV) interacts with its host in three distinct ways in a highly regulated fashion: (i) EBV infects human B lymphocytes and induces proliferation of the infected cells, (ii) it enters into a latent phase in vivo that follows the proliferative phase, and (iii) it can be reactivated giving rise to the production of infectious progeny for reinfection of cells of the same type or transmission of the virus to another individual. In healthy people, these processes take place simultaneously in different anatomical and functional compartments and are linked to each other in a highly dynamic steady-state equilibrium. The development of a genetic system has paved the way for the dissection of those processes at a molecular level that can be studied in vitro, i.e. B-cell immortalization and the lytic cycle leading to production of infectious progeny. Polymerase chain reaction analyses coupled to fluorescent-activated cell sorting has on the other hand allowed a descriptive analysis of the virus-host interaction in peripheral blood cells as well as in tonsillar B cells in vivo. This paper is aimed at compiling our present knowledge on the process of B-cell immortalization in vitro as well as in vivo latency, and attempts to integrate this knowledge into the framework of the viral life cycle in vivo.

Co-localization of the retinoblastoma protein and the Epstein-Barr virus-encoded nuclear antigen EBNA-5

A monoclonal antibody (aRB1C1) raised against an Rb fusion protein detects a limited number (4-10) of relatively large intranuclear foci in an EBV-immortalized cord blood cell line (IB4). These domains also bind an anti-EBNA-5 monoclonal antibody. The Rb antibody reactive sites also co-localize with the SV40 T antigen in transformed monkey cells (COS). The nuclear structures stained by aRB1C1 and EBNA-5 antibodies are distinct from the structures detected with antibodies against centromeric proteins and certain snRNP epitopes. EBNA-5/Rb-positive domains do not selectively react with antibodies against the La antigen known to associate with the small EBV-encoded nuclear RNA species designated as the EBERs.

Variable expression of latent membrane protein in nasopharyngeal carcinoma can be related to methylation status of the Epstein-Barr virus BNLF-1 5'-flanking region

Seven virus-coded proteins, the nuclear proteins EBNA-1 to EBNA-6 and the latent membrane protein (LMP), are regularly expressed in Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines. In nasopharyngeal carcinoma (NPC), only EBNA-1 is regularly expressed; LMP is detected in about 65% of the tumors. In Burkitt's lymphoma tumors only EBNA-1 is expressed. We have recently shown that the methylation patterns of the EBV genome varied between these cell types. In virally transformed lymphoblastoid cell lines of normal origin, the EBV DNA is completely unmethylated. In contrast, in the Burkitt's lymphoma-derived cell line Rael and in a nude mouse-passaged NPC tumor, C15, there was an extensive methylation of CpG pairs. The methylation extended into the coding regions of the two expressed genes, EBNA-1 (in both tumor types) and LMP (in C15). Two presumptive control regions were exempted from this overall methylation: the oriP that contains both an origin of DNA replication and an EBNA-1-dependent enhancer and the 5'-flanking region of the BNLF-1 open reading frame that codes for LMP. The latter was only exempted in the LMP expressing NPC. We have now investigated the relation between expression of LMP and methylation of DNA in the 5'-flanking 1 kb region of BNLF-1, coding for LMP. LMP was methylated in 3 of 12 NPC biopsies that did not express LMP but was partially or totally unmethylated in the remaining 9 that expressed the protein. The three BNLF-1 exons were highly methylated in all the tumors. The oriP region was unmethylated in all the tumors, as in the previously studied Rael cell line and nude mouse-passaged NPC. Also, the BamHI W enhancer region involved in the expression of EBNA nuclear proteins was methylated. None of the biopsies expressed EBNA-2. Our data show that the EBV genomes are highly methylated in NPC tumors. The strong reverse correlation between the methylation of the putative control region of the LMP gene and the expression of LMP suggests that methylation has a role in the regulation of this gene.

Relationship between clinical stage, histopathology and antibody titers against the second Epstein-Barr virus nuclear antigen (EBNA-2) in non-Hodgkin's lymphoma patients

Non-Hodgkin lymphoma (NHL) patients with centroblastic (Cb) or centroblastic-centrocytic (Cb/Cc)-diffuse lymphomas, immunocytoma (IC) and chronic lymphocytic leukemia (CLL) in clinical stages III-IV and with active disease (highly malignant group) were compared to NHL patients with CLL, IC, and centrocytic (Cc) or centroblastic-centrocytic (Cb-Cc)-diffuse/follicular lymphomas, in clinical stages I-II and with inactive disease (low malignant group) based on the presence of antibodies to Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA-1) and 2 (EBNA-2). In the highly malignant group, anti-EBNA-1 geometric mean titers (GMT) were 13.2 (range less than 2-80) and anti-EBNA-2 60.6 (range: 20-320). The ratio between the logarithms of anti-EBNA-1 and anti-EBNA-2 antibody titers was less than 1.0 (mean: 0.32) in all the patients examined. In 6 out of 8 patients of the low malignant group, anti-EBNA-1 titers were higher (mean: 30.1; range 10-160) than anti-EBNA-2 titers (mean: 4.3; range less than 2-80) and the EBNA 1/2 ratio was greater than 1.0. In healthy EBV-seropositive individuals, anti-EBNA-1 GMT were 49 (range: 10-320) and only 5 out of 17 individuals had detectable anti-EBNA-2 titers (GMT: 3; range less than 5-20). The EBNA-1/2 ratio was in all cases greater than 1. Among patients of the highly and low malignant groups, patients with follicular-cell-derived lymphomas had elevated antibody titers against the restricted component of early antigens (EA-R), whereas all patients with IC and 2 out of 4 CLL patients had elevated antibody titers against the diffuse component of early antigens (EA-D). The results indicate that the ratio between anti-EBNA-1 and anti-EBNA-2 antibody titers may be of diagnostic importance in patients with immunodeficiencies.

Host cell-dependent regulation of growth transformation-associated Epstein-Barr virus antigens in somatic cell hybrids

We have analyzed the expression of the three major known growth transformation-associated Epstein-Barr virus (EBV) proteins, EBNA-1, EBNA-2, and latent membrane protein (LMP), in a series of somatic cell hybrids derived from the fusion of EBV-carrying Burkitt lymphoma (BL) lines with EBV-positive or EBV-negative B-cell lines. Independently of the cell phenotype, EBNA-1 was invariably coexpressed in all EBV-carrying hybrids. In hybrids between EBV-carrying, LMP-positive and LMP-negative Burkitt lymphoma lines, LMP was expressed, indicating positive control. Two EBV-negative lymphoma lines, Ramos and BJAB, differed in their ability to express LMP after B95-8 virus-induced conversion and after hybridization with Raji cells. BJAB was permissive while Ramos was nonpermissive for LMP, although both expressed EBNA-2. The EBNA-2-deleted P3HR-1 virus gave the same pattern of LMP expression in these two cells. Our findings indicate that the expression of EBNA-1, EBNA-2, and LMP is regulated by independent mechanisms.

Epstein-Barr virus (EBV) antigen-specific leukocyte migration inhibition in infectious mononucleosis. II. Kinetics of sensitization against five EBV-encoded nuclear proteins and the latent membrane protein

The T cell-mediated immune response of infectious mononucleosis (IM) patients to five Epstein-Barr virus (EBV)-determined nuclear antigens, EBNAs, and to the membrane antigen associated with growth-transformed cells (latent membrane protein, LMP) was measured by the leukocyte migration inhibition (LMI) assay. Two different antigen sources were used: extracts from cells that only expressed EBNA-1, EBNA-2, or LMP after transfection with the corresponding EBV-DNA fragment, and synthetic peptides deduced from the corresponding genes. Patients in the acute phase of the disease failed to respond to EBNA-1, -5, -6, and LMP, but became responsive during convalescence. The majority of the patients responded to EBNA-2 and/or EBNA-3 in the acute phase (9/15 and 12/15, respectively). The response to EBNA-2 and/or EBNA-3 in the acute phase (9/15 and 12/15, respectively). The response to EBNA-3 disappeared more often in convalescence than the response to EBNA-2: 6 of 15 patients were negative to EBNA-2 and 12 of 15 to EBNA-3 during recovery. In addition to its value in the assessment of host sensitization to virus EBV antigens, these studies and the derived hypotheses also provide certain predictions about the predominant antigen expression in the EBV-infected host under normal and pathological conditions that can be subjected to direct experimental tests.

The 5' flanking region of the gene for the Epstein-Barr virus-encoded nuclear antigen 2 contains a cell type specific cis-acting regulatory element that activates transcription in transfected B-cells

We have recently identified the promoter that positions the initiation (cap) site for RNA encoding the Epstein-Barr virus (EBV) determined nuclear antigen 2 (EBNA2) in transfected COS-1 cells. The cells were transfected with recombinant vectors that contained the BamHI WYH region of the EBV genome. In order to delineate regulatory DNA sequences required for the expression of EBNA2 the 5' flanking region of the gene was linked to reporter genes in expression vectors and transfected into EBV genome-negative lymphoid DG75 cells. We demonstrate that several cis-acting elements contribute to a transcriptional enhancer activity found in the region between nucleotides-553 and -86 relative to the cap site. The enhancer was active in lymphoid DG75 cells but not in HeLa cells and stimulated transcription also from the heterologous thymidine kinase (TK) and beta-globin promoters. Nuclear extracts of lymphoid cells contained protein factors that bound to the enhancer. The in vitro introduction of a mutation in the enhancer sequence that substantially reduced the transcription stimulatory activity concurrently blocked the binding of one of the factors.

Detection of antibodies to the Epstein-Barr virus nuclear antigens in the sera from patients with systemic lupus erythematosus

The sera from 65 patients with systemic lupus erythematosus (SLE) were examined by the immunoblotting method to detect antibodies to Epstein-Barr virus (EBV)-associated antigens, especially EBV nuclear antigens (EBNA), and compared with the sera from 66 healthy subjects roughly age- and sex-matched to the patients. Most sera from patients with SLE defined three major EBV-associated antigens with molecular weights (MW) of 70,000 (70K), 90K and 140K in Raji cells, which must correspond to the EBNA-1, 2, and 3, respectively. Approximately 70% of the sera from SLE patients demonstrated the antibodies to the 90K and 140K antigens, whereas the positive rates of these two antibodies were less than 10% in the sera from healthy subjects. The differences of these positive rates of the antibodies between SLE patients and healthy subjects were statistically highly significant. Antibody to EBNA-1 was conspicuously detected in the sera from both SLE patients and healthy subjects, although the difference between the two groups was still significant. The possible role of EBV infection was discussed on the basis of the pathogenesis of SLE.

Antibody response against the Epstein-Barr virus-coded nuclear antigen2 (EBNA2) in different groups of individuals

Specific antibody responses against the 2 major subcomponents of EBNA, EBNA1 and EBNA2 were evaluated, in order to study whether this serological study was beneficial compared to classical EBV serology. During this investigation, 491 sera, obtained from blood donors and patients with Burkitt's lymphoma (BL), nasopharyngeal carcinoma (NPC), infectious mononucleosis (IM), Hodgkin's disease, renal transplantation, rheumatoid arthritis and Human Immunodeficiency Virus (HIV) infection, were tested. While the anti-EBNA1 response followed the classical anti-EBNA/Raji response (99% of anti-EBNA/Raji-positive sera also recognize EBNA1), the anti-EBNA2 response was much less frequent and did not correlate with either anti-EBNA/Raji or anti-EA antibodies. In a control population, 8% of individuals had antiEBNA2 antibodies at titers greater than or equal to 10. The percentage was 45% in NPC and 38% in EBV-associated BL; thus, although not detected in all patients with EBV-associated tumors, anti-EBNA2 serology might be a useful marker in BL and NPC. No antibody was detected in the early course of IM, but in rheumatoid arthritis and in HIV-infected patients, the percentage of positive individuals reached 54 and 68, respectively. Seroconversion to EBNA2 was noted in a few cases, including renal transplant recipients, AIDS patients, and complicated IM. This suggests that in these situations, EBNA 2 serology might represent a useful marker related to modulation of the immune status or EBV reactivation.

Stable transfection of a human lymphoma line by sub-genomic fragments of Epstein-Barr virus DNA to measure humoral and cellular immunity to the corresponding proteins

An Epstein-Barr virus (EBV)-negative human lymphoid B-cell line, DG75, was stably transfected with recombinant selection vectors that carry a subfragment of the BamHI WYH region (nucleotides 44664 to 50628), the BamHI K fragment, or a subfragment of the EcoRI D region (nucleotides 166614 to 170149) of B95-8 EBV DNA. These fragments contain the coding exons for the EBV-determined nuclear antigens EBNA2 and EBNA1, and the membrane antigen LMP, respectively. Antigen expression of the cells was detected by immunofluorescence. EBNA2 was expressed in 80-100% of the transfected cells, in contrast to EBNA1 which was expressed in only 25%, and LMP in only about 5% of the cells. Humoral antibody responses were measured by immunofluorescence and compared to cellular immunity as determined by the leukocyte migration inhibition (LMI) technique. Extracts from transfected cell lines expressing EBNA1, EBNA2 or LMP elicited an LMI response with cells from healthy EBV-seropositive individuals whereas the extract from the parental DG75 cell line did not. The results demonstrate the value of stably transfected cell lines expressing a defined EBV antigen for the monospecific analysis of host responses to the EBV-encoded antigen complex in growth-transformed cells.

Antibody responses to Epstein-Barr virus-determined nuclear antigen (EBNA)-1 and EBNA-2 in acute and chronic Epstein-Barr virus infection

Five distinct Epstein-Barr virus (EBV)-determined nuclear antigens (EBNA-1 to EBNA-5) were recently identified. Antibody responses to these antigens could conceivably differ, and thus prove of serodiagnostic value, in EBV-associated disease processes. As a first step, murine or human cell lines transfected with appropriate EBV DNA fragments and stably expressing either EBNA-1 or EBNA-2 were used to determine the frequency and time of emergence of antibodies to these two antigens in the course of acute and chronic infectious mononucleosis (IM) and to assess their titers in so-called chronic active EBV infections. Following IM, antibodies to EBNA-2 arose first and, after reaching peak titers, declined again in time to lower persistent or even nondetectable levels. Antibodies to EBNA-1 emerged several weeks or months after anti-EBNA-2 and gradually attained the titers at which they persisted indefinitely. The ratios between the anti-EBNA-1 and anti-EBNA-2 titers therefore were generally well below 1.0 during the first 6-12 months after IM and turned to well above 1.0 during the second year. In clear cases of chronic IM, the inversion of this ratio was delayed or prevented. In the less well-defined chronic EBV infections, low ratios were observed in only some of the patients. Because many of these illnesses were not ushered in by a proven IM and often showed EBV-specific antibody profiles within the normally expected range, a causal role of the virus in these cases remains doubtful.

An Epstein-Barr virus (EBV)-determined nuclear antigen (EBNA5) partly encoded by the transformation-associated Bam WYH region of EBV DNA: preferential expression in lymphoblastoid cell lines

Four peptides were synthesized on the basis of amino acid sequences deduced from a highly spliced transcript encoded by the Bam W, Y, and H fragments of the Epstein-Barr virus (EBV) genome [Bodescot, M., Chambraud, J. B., Farrell, P. J. & Perricaudet, M. (1984) EMBO J. 3, 1913-1917]. Rabbit antisera against three of the four peptides identified a nuclear polypeptide that varied between 22 and 70 kDa in molecular size. Four of 20 EBV-positive human sera contained antibodies against this polypeptide. Since this is the fifth EBV-determined nuclear antigen (EBNA) discovered in growth-transformed cells, it is designated EBNA5. The antigen was detected in virus nonproducer lines (less than 0.01% EBV early antigen expression) and is thus not dependent on the viral cycle. It was differentially expressed depending on the origin of the lines. All 10 lymphoblastoid cell lines tested expressed EBNA5, but it could not be detected in 10 of 11 EBV-carrying Burkitt lymphoma lines. Infection of tonsillar lymphocytes with the B95-8 strain of EBV induced six EBNA5-specific polypeptides that varied between 41 and 70 kDa in molecular size with regular increments of 6 kDa. This may be due to the fact that the EBNA5 coding sequence includes the Bam W internal repeat. Parallel infection of the EBV-negative Burkitt lymphoma line Ramos with the same viral substrain did not induce detectable levels of EBNA5, nor was this antigen present in permanently EBV-converted Ramos sublines. These findings imply that the expression of the viral genome varies among B cells having different phenotypes.