Antibodies against a synthetic peptide identify the Epstein-Barr virus-determined nuclear antigen

Assessing Immune Factors in Maternal Milk and Paired Infant Plasma Antibody Binding to Human Rhinoviruses

Before they can produce their own antibodies, newborns are protected from infections by transplacental transfer of maternal IgG antibodies and after birth through breast milk IgA antibodies. Rhinovirus (RV) infections are extremely common in early childhood, and while RV infections often result in only mild upper respiratory illnesses, they can also cause severe lower respiratory illnesses such as bronchiolitis and pneumonia. We used high-density peptide arrays to profile infant and maternal antibody reactivity to capsid and full proteome sequences of three human RVs - A16, B52, and C11. Numerous plasma IgG and breast milk IgA RV epitopes were identified that localized to regions of the RV capsid surface and interior, and also to several non-structural proteins. While most epitopes were bound by both IgG and IgA, there were several instances where isotype-specific and RV-specific binding were observed. We also profiled 62 unique RV-C dominant protein loop sequences characteristic of this species' capsid VP1 protein. Many of these RV-C sites were highly bound by IgG from one-year-old infants, indicating recent or ongoing active infections, or alternatively, a level of cross-reactivity among homologous RV-C sites.

EBNA1: Oncogenic Activity, Immune Evasion and Biochemical Functions Provide Targets for Novel Therapeutic Strategies against Epstein-Barr Virus- Associated Cancers

The presence of the Epstein-Barr virus (EBV)-encoded nuclear antigen-1 (EBNA1) protein in all EBV-carrying tumours constitutes a marker that distinguishes the virus-associated cancer cells from normal cells and thereby offers opportunities for targeted therapeutic intervention. EBNA1 is essential for viral genome maintenance and also for controlling viral gene expression and without EBNA1, the virus cannot persist. EBNA1 itself has been linked to cell transformation but the underlying mechanism of its oncogenic activity has been unclear. However, recent data are starting to shed light on its growth-promoting pathways, suggesting that targeting EBNA1 can have a direct growth suppressing effect. In order to carry out its tasks, EBNA1 interacts with cellular factors and these interactions are potential therapeutic targets, where the aim would be to cripple the virus and thereby rid the tumour cells of any oncogenic activity related to the virus. Another strategy to target EBNA1 is to interfere with its expression. Controlling the rate of EBNA1 synthesis is critical for the virus to maintain a sufficient level to support viral functions, while at the same time, restricting expression is equally important to prevent the immune system from detecting and destroying EBNA1-positive cells. To achieve this balance EBNA1 has evolved a unique repeat sequence of glycines and alanines that controls its own rate of mRNA translation. As the underlying molecular mechanisms for how this repeat suppresses its own rate of synthesis in cis are starting to be better understood, new therapeutic strategies are emerging that aim to modulate the translation of the EBNA1 mRNA. If translation is induced, it could increase the amount of EBNA1-derived antigenic peptides that are presented to the major histocompatibility (MHC) class I pathway and thus, make EBV-carrying cancers better targets for the immune system. If translation is further suppressed, this would provide another means to cripple the virus.

Epstein-Barr virus: more than 50 years old and still providing surprises

It is more than 50 years since the Epstein-Barr virus (EBV), the first human tumour virus, was discovered. EBV has subsequently been found to be associated with a diverse range of tumours of both lymphoid and epithelial origin. Progress in the molecular analysis of EBV has revealed fundamental mechanisms of more general relevance to the oncogenic process. This Timeline article highlights key milestones in the 50-year history of EBV and discusses how this virus provides a paradigm for exploiting insights at the molecular level in the diagnosis, treatment and prevention of cancer.

Herpesvirus serology, aberrant specific immunoglobulin G2 and G3 subclass patterns and Gm allotypes in individuals with low levels of IgG3

One objective of this study was to determine whether IgG3-deficient individuals have an increased frequency of reactivated herpesvirus infections. Serum titres to Epstein-Barr virus (EBV) and human herpesvirus-6 were examined in 10 healthy and in 10 symptomatic persons with serum IgG3 < 0·1 g/l. Atypical titres were found in 16% of the IgG3-deficient individuals. Reactivations of these viruses thus do not seem common in IgG3 deficiency. Antigen-specific IgG responses were also determined. A lowered frequency of IgG3 to an EBV-derived peptide was found only in symptomatic, IgG3-deficient individuals. Levels of IgG2 to a bacterial polysaccharide were lowered in the same group, despite normal serum levels of total IgG2. A functional IgG2 deficiency may contribute to symptoms in IgG3 deficiency. The G3(g) allotype, known to be associated with low total IgG3, dominated in IgG3-deficient persons (13/17) independently of presence or absence of symptoms. A linkage of G3(g) to the G2(n) negative allotype, associated with low IgG2, was equally common irrespective of symptoms. G3(g) and absence of G2(n) seem to be one prerequisite for most of IgG3 deficiency combined with low specific IgG2.

Deiminated Epstein-Barr virus nuclear antigen 1 is a target of anti–citrullinated protein antibodies in rheumatoid arthritis

OBJECTIVE

To test the hypothesis that deimination of viral sequences containing Arg-Gly repeats could generate epitopes recognized by anti-citrullinated protein antibodies (ACPAs) that are present in rheumatoid arthritis (RA) sera.

METHODS

Multiple antigen peptides derived from Epstein-Barr virus (EBV)-encoded Epstein-Barr nuclear antigen 1 (EBNA-1) were synthesized, substituting the arginines with citrulline, and were used to screen RA sera. Anti-cyclic citrullinated peptide antibodies were purified by affinity chromatography and tested on a panel of in vitro deiminated proteins. Their ability to bind in vivo deiminated proteins was evaluated by immunoprecipitation, using EBV-infected cell lines.

RESULTS

Antibodies specific for a peptide corresponding to the EBNA-1(35-58) sequence containing citrulline in place of arginine (viral citrullinated peptide [VCP]) were detected in 50% of RA sera and in <5% of normal and disease control sera. In addition, affinity-purified anti-VCP antibodies from RA sera reacted with filaggrin-derived citrullinated peptides, with deiminated fibrinogen, and with deiminated recombinant EBNA-1. Moreover, anti-VCP antibodies immunoprecipitated, from the lysate of calcium ionophore-stimulated lymphoblastoid cell lines, an 80-kd band that was reactive with a monoclonal anti-EBNA-1 antibody and with anti-modified citrulline antibodies.

CONCLUSION

These data indicate that ACPAs react with a viral deiminated protein and suggest that EBV infection may play a role in the induction of these RA-specific antibodies.

Self-inhibition of synthesis and antigen presentation by Epstein-Barr virus-encoded EBNA1

The glycine-alanine repeat domain (GAr) of Epstein-Barr virus-encoded nuclear antigen 1 (EBNA1) prevents major histocompatibility complex (MHC) class I-restricted presentation of EBNA1 epitopes to cytotoxic T cells. This effect has previously been attributed to the ability of GAr to inhibit its own proteasomal degradation. Here we show, both in vitro and in vivo, that GAr also inhibits messenger RNA translation of EBNA1 in cis and that this effect can be distinguished from its effect on proteasomal degradation. Hence, inhibition of messenger RNA translation, but not protein degradation, is essential to prevent antigen presentation on MHC class I molecules. Thus, by minimizing translation of the EBNA1 transcript, cells expressing EBNA1 avoid cytotoxic T cell recognition. At the same time, blocking degradation maintains the EBNA1 expression level.

Epstein-Barr virus: induction and control of cell transformation

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

Avoiding proteasomal processing: the case of EBNA1

Ubiquitin/proteasome-dependent proteolysis is involved in the regulation of a large variety of cellular processes including cell cycle progression, tissue development and atrophy, flux of substrates through metabolic pathways, selective elimination of abnormal proteins and processing of intracellular antigens for major histocompatibility complex (MHC) class I-restricted T-cell responses. Many viruses tamper with this proteolytic machinery by encoding proteins that interact with various components of the pathway. A particularly interesting example of a viral protein that interferes with proteasomal processing is the Epstein-Barr virus (EBV) nuclear antigen-1 (EBNA1). EBNA1 contains an internal repeat exclusively composed of glycines and alanines that inhibits in cis the presentation of MHC class I-restricted T-cell epitopes and prevents ubiquitin/proteasome-dependent proteolysis in vitro and in vivo. The glycine-alanine repeat acts as a transferable element on a variety of proteasomal substrates and may therefore provide a new approach to the modification of cellular proteins for therapeutic purposes.

Manipulation of immune responses by Epstein–Barr virus

Epstein-Barr virus (EBV) infects and persists for life in the majority of the human population. Persistence is achieved through a combination of strictly regulated programs of latent infection in B-cells and chronic reactivation of virus replication in lymphoid tissue and mucosal surfaces. The resulting multiple patterns of virus-host interaction have selected unique strategies of immune escape. T-cell mediated immunity plays a central role in the control of EBV latency and several immune escape mechanism that protect the virus at this stage of its life circle have been characterized in details. In contrast, the contribution of innate immunity and the immune regulation of productive infection are largely unexplored areas that may yield important clues on the establishment and maintenance of EBV persistence. This review summarizes well known and emerging mechanisms of EBV immune escape that may reveal new strategies of immunoregulation and promote new approaches to the prophylaxis and treatment of EBV associated diseases.

The PE multigene family: a 'molecular mantra' for mycobacteria

The PE multigene family of Mycobacterium tuberculosis is remarkable in that it is composed of approximately 100 highly homologous genes that are found only in mycobacteria. Early evidence suggests that proteins encoded by certain members of this gene family could be present in the mycobacterial cell wall, impact antigen-presentation pathways and the ensuing host immune responses, and also provide a mechanism for generating antigenic diversity in mycobacteria.

Degradation signals in ErbB-2 dictate proteasomal processing and immunogenicity and resist protection by cis glycine-alanine repeat

ErbB-2 is ubiquitinated and degraded when dissociated from its membrane chaperone or bound by specific antibody. Reagents which induce such degradation have demonstrated antitumor activity and may impact ErbB-2 immunogenicity. To further understand ErbB-2 degradation and immunogenicity, a glycine-alanine repeat (GAr) or the reverse proline-alanine repeat (PAr) which protects certain proteins from proteasome degradation, was inserted after amino acid 5 (GAr5/PAr5) or 55 (GAr55/PAr55) of ErbB-2. When dissociated from the membrane with geldanamycin, E2-GAr5 and E2-PAr5 were not protected and still ubiquitinated and degraded by the proteasome, despite the presence of GAr. Insertional mutagenesis with GAr sequences at a.a. 55 of E2 enhanced proteasome degradation rendering E2-GAr55 and E2-PAr55 unstable on the membrane, but rescued in the cytosol by proteasome inhibitors. Immunization with E2-GAr induced antitumor immunity and CTL which lysed tumor cells expressing chimeric E2-GAr or wild-type E2 proteins, demonstrating efficient presentation through MHC I pathway. Improved understanding of the strong degradation signals in ErbB-2 may facilitate the development of anticancer agents or vaccines.

Comparative immune response to PE and PE_PGRS antigens of Mycobacterium tuberculosis

Sequencing of the entire genome of Mycobacterium tuberculosis identified a novel multigene family composed of two closely related subfamilies designated PE and PE_PGRS. The major difference between these two families is the presence of a domain containing numerous Gly-Ala repeats extending to the C terminus of the PE_PGRS genes. We have used a representative PE_PGRS gene from M. tuberculosis, Rv1818c (1818PE_PGRS), and its amino-terminal PE region (1818PE), to investigate the immunological response to these proteins during experimental tuberculosis and following immunization with DNA constructs. During infection of mice with M. tuberculosis, a significant humoral immune response was observed against recombinant 1818PE_PGRS but not toward the 1818PE protein. Similarly, immunization with a 1818PE_PGRS DNA construct induced antibodies directed against 1818PE_PGRS but not against 1818PE proteins, and no humoral response was induced by 1818PE DNA. These results suggest that certain PE_PGRS genes are expressed during infection of the host with M. tuberculosis and that an antibody response is directed solely against the Gly-Ala-rich PGRS domain. Conversely, splenocytes from 1818PE-vaccinated mice but not mice immunized with 1818PE_PGRS secreted gamma interferon following in vitro restimulation and demonstrated protection in the mouse tuberculosis challenge model. These results suggest that the PE vaccine can elicit an effective cellular immune response and that immune recognition of the PE antigen is influenced by the Gly-Ala-rich PGRS domain.

Differential immunogenicity of Epstein-Barr virus latent-cycle proteins for human CD4(+) T-helper 1 responses

Human CD4(+) T-helper 1 cell responses to Epstein-Barr virus (EBV) infection are likely to be important in the maintenance of virus-specific CD8(+) memory and/or as antiviral effectors in their own right. The present work has used overlapping peptides as stimulators of gamma interferon release (i) to identify CD4(+) epitopes within four EBV latent-cycle proteins, i.e., the nuclear antigens EBNA1 and EBNA3C and the latent membrane proteins LMP1 and LMP2, and (ii) to determine the frequency and magnitude of memory responses to these proteins in healthy virus carriers. Responses to EBNA1 and EBNA3C epitopes were detected in the majority of donors, and in the case of EBNA1, their antigen specificity was confirmed by in vitro reactivation and cloning of CD4(+) T cells using protein-loaded dendritic cell stimulators. By contrast, responses to LMP1 and LMP2 epitopes were seen much less frequently. EBV latent-cycle proteins therefore display a marked hierarchy of immunodominance for CD4(+) T-helper 1 cells (EBNA1, EBNA3C >> LMP1, LMP2) which is different from that identified for the same proteins with respect to CD8(+)-T-cell responses (EBNA3C > EBNA1 > LMP2 >> LMP1). Furthermore, the range of CD4(+) memory T-cell frequencies in peripheral blood of healthy virus carriers was noticeably lower and narrower than the corresponding range of latent antigen-specific CD8(+)-T-cell frequencies.

Inhibition of proteasomal degradation by the gly-Ala repeat of Epstein-Barr virus is influenced by the length of the repeat and the strength of the degradation signal

The Gly-Ala repeat (GAr) of the Epstein-Barr virus nuclear antigen-1 is a transferable element that inhibits in cis ubiquitin/proteasome-dependent proteolysis. We have investigated this inhibitory activity by using green fluorescent protein-based reporters that have been targeted for proteolysis by N end rule or ubiquitin-fusion degradation signals, resulting in various degrees of destabilization. Degradation of the green fluorescent protein substrates was inhibited on insertion of a 25-aa GAr, but strongly destabilized reporters were protected only partially. Protection could be enhanced by increasing the length of the repeat. However, reporters containing the Ub-R and ubiquitin-fusion degradation signals were degraded even in the presence of a 239-aa GAr. In accordance, insertion of a powerful degradation signal relieved the blockade of proteasomal degradation in Epstein-Barr virus nuclear antigen-1. Our findings suggest that the turnover of natural substrates may be finely tuned by GAr-like sequences that counteract targeting signals for proteasomal destruction.

Expression of K13/v-FLIP gene of human herpesvirus 8 and apoptosis in Kaposi's sarcoma spindle cells

BACKGROUND

Human herpesvirus 8 (HHV8) infection is associated with all forms of Kaposi's sarcoma (KS). The HHV8 genome locus ORFK13-72-73 (ORF = open reading frame) encodes proteins that may be important in HHV8-mediated pathogenesis, i.e., the latency-associated nuclear antigen (encoded by ORF73), viral-cyc-D (v-cyc-D), a viral homologue of cellular cyclin D (encoded by ORF72), and viral-FLIP (v-FLIP), a homologue of the cellular FLICE (Fas-associated death domain-like interleukin 1 beta-converting enzyme) inhibitory protein (encoded by ORFK13; is an inhibitor of apoptosis [programmed cell death]). Through differential splicing events, this locus expresses individual RNA transcripts that encode all three proteins (tricistronic transcripts) or just two of them (v-FLIP and v-cyc-D; bicistronic transcripts). We examined expression of these transcripts in KS tissues.

METHODS

We collected tissues from patients with KS of different stages. By use of an optimized in situ hybridization procedure, we examined different ORFK13-72-73 locus transcripts in HHV8-infected cells in skin lesions and in one adjacent lymph node. Apoptosis in KS lesions was determined by use of an in situ assay.

RESULTS AND CONCLUSIONS

Our results indicate the following: 1) Transcripts from the ORFK13-72-73 locus appear to be spliced differentially in latently infected KS cells in skin lesions and in HHV8-infected cells in lymph nodes; specifically, ORFK13-ORF72 bicistronic transcripts were expressed abundantly in KS cells, whereas ORFK13-ORF72-ORF73 tricistronic transcripts were detected only in lymph node cells. 2) Sequences encoding the antiapoptotic protein v-FLIP are expressed at very low levels in early KS lesions, but expression increases dramatically in late-stage lesions. 3) The increase in expression of v-FLIP-encoding transcripts is associated with a reduction in apoptosis in KS lesions.

IMPLICATIONS

These data suggest that functional v-FLIP is produced in vivo and that antiapoptotic mechanisms may be involved in the rapid growth of KS lesions, where only a few cells undergoing mitosis are generally observed.

A minimal glycine-alanine repeat prevents the interaction of ubiquitinated I kappaB alpha with the proteasome: a new mechanism for selective inhibition of proteolysis

The Epstein-Barr virus nuclear antigen 1 contains a glycine-alanine repeat that inhibits in cis MHC class I-restricted presentation. We report here that insertion of a minimal glycine-alanine repeat motif in different positions of I kappaB alpha protects this NF-kappaB inhibitor from signal-induced degradation dependent on ubiquitin-proteasome, and decreases its basal turnover in vivo resulting in constitutive dominant-negative mutants. The chimeras are phosphorylated and ubiquitinated in response to tumor necrosis factor alpha, but are then released from NF-kappaB and fail to associate with the proteasome. This explains how functionally competent I kappaB alpha is protected from proteasomal disruption and identifies the glycine-alanine repeat as a new regulator of proteolysis.

Murine cytotoxic T lymphocytes recognize an epitope in an EBNA-1 fragment, but fail to lyse EBNA-1-expressing mouse cells

Major histocompatibility complex class I-restricted cytotoxic T lymphocytes (CTLs) specific for epitopes within eight of the nine Epstein Barr Virus (EBV)-encoded latency-associated proteins have been recovered from EBV-infected human subjects by restimulation of lymphocytes in vitro. However, human class I-restricted CTL responses capable of recognizing EBNA-1 expressing cells were not detected in these studies. We have raised a murine CTL line that recognizes an epitope within EBNA-1 by immunizing mice with a vaccinia virus encoding a COOH-terminal EBNA-1 fragment. This novel CTL line was used to investigate whether the epitope (positions 509-517 in EBNA-1, presented through Kd) was presented to CTL by mouse cells expressing full-length EBNA-1 or a deletion mutant of EBNA-1, lacking the Glycine-Alanine (Gly-Ala)-rich region. Cells expressing full-length EBNA-1 are not lysed by the CTL line, whereas cells expressing the Gly-Ala deletion mutant are recognized. These results suggest that epitopes from full-length EBNA-1 are poorly presented, and that the Gly-Ala-rich region is responsible for this phenomenon. The inefficient presentation of EBNA-1-derived epitopes may explain the absence or rarity of EBNA-1-specific CTLs in vivo, a strategy that may allow EBV to maintain persistence within the immunocompetent host without being eliminated by CTLs.

Inhibition of ubiquitin/proteasome-dependent protein degradation by the Gly-Ala repeat domain of the Epstein-Barr virus nuclear antigen 1

The Epstein-Barr virus (EBV) encoded nuclear antigen (EBNA) 1 is expressed in latently infected B lymphocytes that persist for life in healthy virus carriers and is the only viral protein regularly detected in all EBV associated malignancies. The Gly-Ala repeat domain of EBNA1 was shown to inhibit in cis the presentation of major histocompatibility complex (MHC) class I restricted cytotoxic T cell epitopes from EBNA4. It appears that the majority of antigens presented via the MHC I pathway are subject to ATP-dependent ubiquitination and degradation by the proteasome. We have investigated the influence of the repeat on this process by comparing the degradation of EBNA1, EBNA4, and Gly-Ala containing EBNA4 chimeras in a cell-free system. EBNA4 was efficiently degraded in an ATP/ubiquitin/proteasome-dependent fashion whereas EBNA1 was resistant to degradation. Processing of EBNA1 was restored by deletion of the Gly-Ala domain whereas insertion of Gly-Ala repeats of various lengths and in different positions prevented the degradation of EBNA4 without appreciable effect on ubiquitination. Inhibition was also achieved by insertion of a Pro-Ala coding sequence. The results suggest that the repeat may affect MHC I restricted responses by inhibiting antigen processing via the ubiquitin/proteasome pathway. The presence of regularly interspersed Ala residues appears to be important for the effect.

Synthetic peptides deduced from the amino acid sequence of Epstein-Barr virus nuclear antigen 6 (EBNA 6): antigenic properties, production of monoreactive reagents, and analysis of antibody responses in man

Studies on the antibody responses to various Epstein-Barr virus (EBV) antigens have been instrumental in the understanding of the seroepidemiology and diagnosis of this viral infection and the subsequent carrier state. While antibodies to the viral capsid antigen (VCA), early antigen (EA), and nuclear antigens 1 and 2 (EBNA 1 and 2) have been well characterized, the antibody response to the other nuclear antigens is not well understood. EBNA 6 is expressed by lymphoblasts during acute EBV infection and may be an important antigen for diagnosis and evaluation of the immune response. In order to analyze the antibody response to EBNA 6, ten peptides (20-21 amino acids), deduced from the EBNA 6 coding region, were synthesized and evaluated for antigenicity by ELISA. One peptide (p-63; PAPQAPYQGYQEPPAPQAPY) derived from the amino acid repeats showed the highest specific reactivity with human sera. This peptide was evaluated further for detection of human EBNA 6-reactive antibodies. Forty-two of forty-nine (86%) EBV-seropositive healthy donors had p-63-specific IgG reactivity, while none of 50 EBV-seronegative patients reacted with the p-63 peptide. Twenty-two of fifty-one (43%) patients with ongoing primary EBV infection had detectable p-63-specific IgG. Serum samples drawn sequentially from patients during and after primary EBV infection revealed an increase in p-63-reactive IgG over time.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of antigen processing by the internal repeat region of the Epstein-Barr virus nuclear antigen-1

The Epstein-Barr virus (EBV)-encoded nuclear antigen (EBNA1) is expressed in latently EBV-infected B lymphocytes that persist for life in healthy virus carriers, and is the only viral protein regularly detected in all malignancies associated with EBV. Major histocompatibility complex (MHC) class I-restricted, EBNA1-specific cytotoxic T lymphocyte (CTL) responses have not been demonstrated. Using recombinant vaccinia viruses encoding chimaeric proteins containing an immunodominant human leukocyte antigen A11-restricted CTL epitope, amino acids 416-424 of the EBNA4 protein, inserted within the intact EBNA1, or within an EBNA1 deletion mutant devoid of the internal Gly-Ala repetitive sequence, we demonstrate that the Gly-Ala repeats generate a cis-acting inhibitory signal that interferes with antigen processing and MHC class I-restricted presentation. Insertion of the Gly-Ala repeats downstream of the 416-424 epitope inhibited CTL recognition of a chimaeric EBNA4 protein. The results highlight a previously unknown mechanism of viral escape from CTL surveillance, and support the view that the resistance of cells expressing EBNA1 to rejection mediated by CTL is a critical requirement for EBV persistence and pathogenesis.

Expression of Epstein-Barr-virus-related nuclear antigens and B-cell markers in lymphomas of SIV-immunosuppressed monkeys

Simian-immunodeficiency-virus(SIV)-infected cynomolgus monkeys develop B-cell lymphomas in approximately one third of the cases. We have now studied the expression of cynomolgus-Epstein-Barr-virus(cyno-EBV) nuclear antigens in 13 cyno-EBV-carrying SIVsm-associated monkey lymphomas and established cell lines from 3 of these tumors. Immunoblots of cell lysates were probed with polyspecific and monospecific reagents directed against human EB-virus EBNAI-6, and against the membrane protein LMPI. An EBNA2-cross-reacting protein was demonstrated in 8 lymphoma tissues (8/13) and in the 3 cell lines derived from the tumors. All tumors expressed a polypeptide with 50 to 55 kDa molecular weight, which cross-reacted with some antibodies to EBNAI. Absorption experiments with normal monkey tissue showed that this polypeptide was specific for the cyno-EBV-carrying lymphoma cells. Equivalents of EBNA3-6 and LMPI could not be detected. Immunophenotypical characterization showed that the monkey lymphomas were similar to human HIV-associated B-cell lymphomas. Malignant B-cell lymphomas in experimentally SIVsm-infected cynomolgus monkeys can be a model for EBV-associated lymphomagenesis in immunodeficiency states.

Autoantibodies from patients with systemic lupus erythematosus bind a shared sequence of SmD and Epstein-Barr virus-encoded nuclear antigen EBNA I

SmD is one of the small nuclear ribonucleoproteins frequently targeted by autoantibodies in systemic lupus erythematosus. We isolated and characterized the antibodies present in lupus sera that are specific for the C-terminal region of SmD (sequence 95-119). This region is highly homologous to sequence 35-58 of the EBNA I antigen, one of the nuclear antigens induced by infection with Epstein-Barr virus. Antibodies affinity purified over a peptide 95-119 column were able to recognize this sequence in the context of the whole SmD molecule, as they reacted with blotted recombinant SmD. Anti-SmD 95-119 antibodies bound also the EBNA I 35-58 peptide and detected the EBNA I molecule in a total cell extract from Epstein-Barr virus-infected lines. A population of anti-SmD antibodies is, therefore, able to bind an epitope shared by the autoantigen and the viral antigen EBNA I. To investigate the involvement of this shared epitope in the generation of anti-SmD antibodies, we immunized mice with the EBNA I 35-58 peptide. Sera from immunized animals displayed the same pattern of reactivity of spontaneously produced anti-SmD antibodies. They reacted in fact with the EBNA peptide as well as with SmD 95-119 and recombinant SmD. These data suggest that molecular mimicry may play a role in the induction of anti-SmD autoantibodies.

Decreased expression of E-cadherin and increased invasive capacity in EBV-LMP-transfected human epithelial and murine adenocarcinoma cells

The EBV-encoded membrane protein LMP is one of 9 viral proteins regularly expressed in virally immortalized B lymphocytes. It is expressed in EBV-carrying lymphoblastoid cell lines of normal origin and in the majority of the poorly differentiated nasopharyngeal carcinomas, but not in Burkitt lymphomas. LMP has been reported to transform rodent fibroblasts, to inhibit epithelial differentiation and to alter morphology and cytokeratin expression in an in vitro immortalized human keratinocyte cell-line, RHEK-I. We now report that an LMP-transfected mouse mammary carcinoma line, SHG, exhibits a similar morphological change to that previously described in the LMP-transfected RHEK-I. In the LMP-transfected RHEK-I and SHG cells, we observed a decreased expression of the calcium-dependent adhesion molecule E-cadherin. The LMP-transfected RHEK-I cells were capable of invading type-I collagen gels while the control cells were not. The LMP-transfected SHG cells showed a significantly higher invasive capacity than the original cell line.

Herpesvirus serology, aberrant specific immunoglobulin G2 and G3 subclass patterns and Gm allotypes in individuals with low levels of IgG3

One objective of this study was to determine whether IgG3-deficient individuals have an increased frequency of reactivated herpesvirus infections. Serum titres to Epstein-Barr virus (EBV) and human herpesvirus-6 were examined in 10 healthy and in 10 symptomatic persons with serum IgG3 < 0.1 g/l. Atypical titres were found in 16% of the IgG3-deficient individuals. Reactivations of these viruses thus do not seem common in IgG3 deficiency. Antigen-specific IgG responses were also determined. A lowered frequency of IgG3 to an EBV-derived peptide was found only in symptomatic, IgG3-deficient individuals. Levels of IgG2 to a bacterial polysaccharide were lowered in the same group, despite normal serum levels of total IgG2. A functional IgG2 deficiency may contribute to symptoms in IgG3 deficiency. The G3(g) allotype, known to be associated with low total IgG3, dominated in IgG3-deficient persons (13/17) independently of presence or absence of symptoms. A linkage of G3(g) to the G2(n) negative allotype, associated with low IgG2, was equally common irrespective of symptoms. G3(g) and absence of G2(n) seem to be one prerequisite for most of IgG3 deficiency combined with low specific IgG2.

Recognition of the Epstein-Barr virus-encoded nuclear antigens EBNA-4 and EBNA-6 by HLA-A11-restricted cytotoxic T lymphocytes: implications for down-regulation of HLA-A11 in Burkitt lymphoma

Evasion from cytotoxic T-lymphocyte (CTL) surveillance may be an important step in the pathogenesis of Epstein-Barr virus (EBV)-carrying Burkitt lymphoma (BL) as suggested by the consistent down-regulation of all transformation-associated viral antigens, except EBV nuclear antigen 1 (EBNA-1), and of certain HLA class I alleles in BL biopsies and cell lines that maintain the tumor cell phenotype in vitro. The most common HLA class I defect recorded in BL lines is a selective down-regulation of HLA-A11. To gain some insight into the role of HLA-A11 down-regulation in pathogenesis of BL, we have investigated the target specificity of HLA-A11-restricted CTLs derived by stimulation of lymphocytes from three EBV-seropositive individuals with autologous EBV-transformed lymphoblastoid cell lines. Recombinant vaccinia viruses carrying the coding sequences for EBNA-1, -2A, -2B, -5, -3, -4, and -6 (also known as EBNA-1, -2A, -2B, -LP, -3a, -3b, and -3c, respectively) and EBV latent membrane protein 1 were used to induce high levels of expression of the relevant EBV antigen in fibroblasts derived from HLA class I-matched individuals. EBNA-4-expressing fibroblasts were the predominant target of HLA-A11-restricted CTLs in all three donors. A less pronounced and less regular EBNA-6-specific cytotoxic component was found in two of the donors.

Use of enzyme-linked immunosorbent assays with chimeric fusion proteins to titrate antibodies against Epstein-Barr virus nuclear antigen 1

Two new enzyme-linked immunosorbent assays (ELISAs) with chimeric fusion polypeptides for the detection of human antibodies specific to Epstein-Barr virus nuclear antigen 1 (EBNA-1) are described. One is an indirect ELISA with affinity-purified beta-galactosidase-EBNA-1 fusion protein as the antigen. The other is a "sandwich" assay based on the use of anti-beta-galactosidase antibody to capture beta-galactosidase-EBNA-1 fusion proteins in bacterial extracts. A good correlation was shown between antibody titers determined by the ELISA with the EBNA-1 fusion proteins and those determined by a conventional anticomplement immunofluorescence test which is being widely performed with Raji cells for the purpose of research and clinical diagnosis. The advantage of the ELISAs for seroepidemiologic studies on Epstein-Barr virus was demonstrated by sensitive detection of marginal immunoglobulin G antibody to the EBNA-1 domain in serum samples from patients with infectious mononucleosis.

Identification and immunochemical characterization of IgA in sera of patients with mammary tumors

It has been reported that several types of human cancer are associated with elevated levels of class-A immunoglobulins (Ig) and IgA-containing immune complexes. Moreover, most previous work has come up against the lack of IgA reactivity for chemically defined antigen (Ag). To overcome this, we first evaluated possible immunological binding in sera of patients with mammary tumors or malignant hematologic diseases and controls on a mouse monoclonal anti-idiotypic antibody (Ab2), internal image of conjugated benzo(a)pyrene (BP) coated on well plates. Using this indirect ELISA, a statistically highly significant immunological binding was found in sera of patients with mammary tumors of every grade, type and size. This immunological binding was linked to the IgA isotype. Second, we performed competition experiments between a BP conjugate coated on well-plates and anti-anti-"BP-like" antibodies (Ab) previously incubated with rabbit idiotypic antibodies (Ab1) directed against conjugated BP. A part of these anti-anti-BP-like Ab, raised in rabbits immunized with human IgA of patients with mammary tumors, recognized the Ag-combining site of polyclonal Ab1, previously developed in a rabbit immunized with BP conjugates. It appears that part of the human Ig from sera of patients with mammary tumors shares common idiotopes with rabbit polyclonal Ab1 raised against conjugated BP.

Epstein-Barr virus nuclear antigen 1 linear epitopes that are reactive with immunoglobulin A (IgA) or IgG in sera from nasopharyngeal carcinoma patients or from healthy donors

The entire amino acid sequence of the unique region of the EBNA 1 protein was synthesized as a set of 41 20-residue peptides with an overlap of 10 amino acids. The peptides were tested in the enzyme-linked immunosorbent assay for reactivity with immunoglobulin A (IgA) and IgG in sera from 50 patients with nasopharyngeal carcinoma (NPC) as compared with 36 serum samples from healthy Epstein-Barr virus (EBV)-seropositive donors and 5 serum samples from EBV-negative donors. The most immunoreactive peptide for both IgA and IgG binding was localized to the glycine-alanine repeat domain of the antigen. In the unique regions, 16 immunoreactive peptides were found. Of these, four were reactive with IgG but not IgA and three peptides were reactive with IgA but not IgG in NPC sera. In addition, several IgA and IgG epitopes on the carboxy-terminal region were specifically reactive with NPC sera, but unreactive with sera from healthy EBV-positive donors. The results suggest that EBV serology specific for individual epitopes may provide additional useful information not available by conventional serology with whole antigens or the EBNA complex.

Human cytomegalovirus structural proteins: immune reaction against pp150 synthetic peptides

In the present study, several peptides of the major structural antigen (pp150) of human cytomegalovirus (CMV) have been chemically synthesized and tested by a modified slot blotting procedure for their ability to bind CMV-specific immunoglobulin G (IgG) and IgM present in human sera. The sequences of the peptides were deduced on the basis of either (i) their presence in a fusion protein already known to be frequently recognized by human antibody or (ii) their high content of hydrophilic amino acids as deduced from the published nucleotide sequence. An important IgM-binding epitope was found to be located in the last 38 amino acids at the carboxy terminus of the molecule. This region reacts with anti-CMV IgM present in the great majority (83.3%) of IgM-positive human sera, and adsorption experiments have shown that IgM titers to the entire pp150 decrease 25 to 50% in most sera previously absorbed with this region. The overall results obtained endorse the continued synthesis of other sequences in order to define a group of peptides sensitive and specific enough to replace the virus and infected cells as an antigenic substrate in the serological evaluation of anti-CMV antibody.

Expression of Epstein-Barr virus-encoded growth-transformation-associated proteins in lymphoproliferations of bone-marrow transplant recipients

The expression of Epstein-Barr virus (EBV)-encoded, growth-transformation-associated proteins was studied in lymphoproliferations of 9 allogeneic bone-marrow transplant (BMT) recipients. Immunoblots of cell lysates were probed with polyspecific and monospecific antisera directed against EBNA 1, 2, 3 and 6, and the membrane protein LMP. All tumors expressed EBNA 1 and LMP. EBNA 2 was detected in the tumors of 8 patients, and EBNA 3 and 6 in the tumors of 5 patients. The LMP regulatory sequences, 5' of the LMP gene, were totally unmethylated in all 7 cases, while the coding sequences of LMP and EBNA 2 were more methylated in CpG dinucleotides. EBV-transformed lymphoblastoid cell lines (LCL) express EBNA 1 to 6 and LMP; in contrast, Burkitt lymphomas express only EBNA 1. In vitro experiments have shown that EBNA 2, 3 and LMP can generate targets for cytotoxic T cells (CTL). These combined observations are consistent with the hypothesis that the EBV-associated lymphoproliferative disease of the BMT recipients escapes CTL-mediated rejection due to the failure of host immunosurveillance rather than to the down-regulation of immunogenic EBV-encoded antigens.

Epstein-Barr virus (EBV)-associated lymphoproliferative disease in the SCID mouse model: implications for the pathogenesis of EBV-positive lymphomas in man

When human peripheral blood lymphocytes (PBLs) from Epstein-Barr virus (EBV)-seropositive donors are injected intraperitoneally into SCID mice, EBV+ B cell tumors develop within weeks. A preliminary report (Mosier, D. E., R. J. Gulizia, S. M. Baird, D. D. Richman, D. B. Wilson, R. I. Fox, and T. J. Kipps, 1989. Blood. 74(Suppl. 1):52a) has suggested that such tumors resemble the EBV-positive malignancy, Burkitt's lymphoma. The present work shows that generally the human (hu) PBL-SCID tumors are distinct from Burkitt's lymphoma and instead resemble lymphoblastoid cell lines (LCLs) generated by EBV-infection of normal B cells in vitro in terms of: (a) their cell surface phenotype, with expression of B cell activation antigens and adhesion molecules, (b) normal karyotype, and (c) viral phenotype, with expression of all the transformation-associated EBV latent proteins and, in a minority of cells, productive cycle antigens. Indeed, in vitro-transformed LCLs also grow when inoculated into SCID mice, the frequency of tumor outgrowth correlating with the in vitro growth phenotype of the LCL which is itself determined by the identity of the transforming virus (i.e., type 1 or type 2 EBV). Histologically the PBL-derived hu-SCID tumors resemble the EBV+ large cell lymphomas that develop in immuno-suppressed patients and, like the human tumors, often present at multiple sites as individual monoclonal or oligoclonal foci. The remarkable efficiency of tumor development in the hu-SCID model suggests that lymphomagenesis involves direct outgrowth of EBV-transformed B cells without requirement for secondary genetic changes, and that selection on the basis of cell growth rate alone is sufficient to explain the monoclonal/oligoclonal nature of tumor foci. EBV+ large cell lymphoma of the immunosuppressed may arise in a similar way.

EBNA size polymorphism can be used to trace Epstein-Barr virus spread within families

The Epstein-Barr virus (EBV)-determined nuclear antigens EBNA 1, 2, 3, 4, and 6, regularly expressed in EBV-transformed lymphoblastoid cell lines, vary in size among viral strains. We have used this characteristic to trace the spread of the virus within seven families by using an approach called Ebnotyping. Among 33 evaluable individuals, 3 were EBV seronegative, and 17 different EBV strains could be isolated from the peripheral blood or throat washes of the remaining 30. All unrelated persons carried different strains. The EBV strain carried by 19 persons was also found in 1 or more family members. The same viral strain was carried by two members in five families, by three members in the sixth, and by five members in the seventh. The paternal strain was isolated from one child in two families, and the maternal strain was isolated from one or more children in three families. EBV was isolated from both blood and throat wash in six individuals. The Ebnotypes of both derived lymphoblastoid cell lines were identical within each individual. These results indicate that spread within families may be a relatively common route of EBV transmission. The number of horizontal transmission events required to generate diversification of the Ebnotype will require larger epidemiological studies.

Serum and salivary IgA antibodies against a defined epitope of the Epstein-Barr virus nuclear antigen (EBNA) are elevated in nasopharyngeal carcinoma

The Epstein-Barr virus nuclear antigen I (EBNA I) is the only latent EBV antigen consistently expressed in malignant tissues of the nasopharynx. A 20-amino-acid synthetic peptide, p107 contains a major epitope of EBNA I. We tested sera from 210 patients with nasopharyngeal carcinoma (NPC) and from 128 normal individuals (NHS) for IgA antibodies to p107 using an enzyme-linked immunosorbent assay (ELISA). Whereas 191/210 (91%) of NPC patients had IgA antibodies to p107, only 17/128 (13.3%) of NHS had such antibodies and only 6/57 (10.5%) of sera from patients with malignancies other than NPC had IgA-p107 reactivity. Thirty-nine salivary samples from 46 NPC patients (84.8%) also contained IgA-p107 antibodies whereas only 3/42 (7.1%) of normal saliva samples were IgA-p107 positive. The results suggest that IgA antibodies to EBNA I may become a useful, easily measurable, marker for NPC.

Homology of cytokine synthesis inhibitory factor (IL-10) to the Epstein-Barr virus gene BCRFI

Complementary DNA clones encoding mouse cytokine synthesis inhibitory factor (CSIF; interleukin-10), which inhibits cytokine synthesis by TH1 helper T cells, were isolated and expressed. The predicted protein sequence shows extensive homology with an uncharacterized open reading frame, BCRFI, in the Epstein-Barr virus genome, suggesting the possibility that this herpes virus exploits the biological activity of a captured cytokine gene to enhance its survival in the host.

Mapping of linear epitopes of human papillomavirus type 16: the L1 and L2 open reading frames

Certain types of human papillomavirus (HPV), notably HPV type 16, are associated with flat or inverted proliferative lesions of the cervix uteri that can progress to malignancy. As a first step towards the serological study of the epidemiology of HPV, we have synthesized the entire amino acid sequences of the 2 major viral capsid proteins of HPV type 16, L1 and L2, as a set of 66 synthetic 20-residue peptides with an overlap of 5 amino acids. The peptides were tested for reactivity with IgA, IgG and IgM antibodies in the sera of 30 patients with HPV-16-carrying cervical neoplasms. Both IgG and IgM antibody responses were detected, but most of the reactivity found was of the IgA class. The most immunoreactive peptides were further analyzed for reactivity with sera from 22 patients with parotid gland tumors and with sera from 38 healthy individuals. The L2-encoded protein contained only one major linear epitope, which was not specific for HPV-16-carrying neoplasms. In contrast, the L1-encoded protein contained several epitopes that were regularly immunoreactive with antibodies present in the sera of patients with HPV-16-carrying cervical neoplasms, but only rarely so in the sera of patients with other tumors or of healthy individuals.

Effect of the EBNA-2 gene on the surface antigen phenotype of transfected EBV-negative B-lymphoma lines

Two EBV-negative B-lymphoma cell lines with different phenotypes were transfected with the Epstein-Barr virus EBNA-2 gene. The effects on the expression of 8 B-cell surface markers were analyzed by immunofluorescence methods. In one of the EBNA-2 transfected cell lines, the expression of the CR2 receptor CD21 was induced and the expression of CD23 was enhanced. The results suggest that the EBNA-2 gene is involved in the regulation of CD21 and CD23 in EBV-carrying cells.

Identical IgM antibodies recognizing a glycine-alanine epitope are induced during acute infection with Epstein-Barr virus and cytomegalovirus

We studied antibody production in serial serum samples from patients with acute Epstein-Barr virus (EBV) and cytomegalovirus (CMV) infections. Sera were analyzed both by enzyme-linked immunosorbent assay (ELISA) using a synthetic peptide (P62) derived from the glycine-alanine repeating region of the Epstein-Barr nuclear antigen (EBNA-1) and by immunoblotting. In prior studies, we have shown that patients with acute EBV infection make IgM antibodies that react with this peptide, that recognize a viral-specific protein (EBNA-1), and that bind with a number of proteins present in uninfected cells; however, antibody binding to these autoantigens was inhibited by the peptide. IgG antibodies reactive with the peptide did not appear until months after the disease and were specific for the EBNA-1 protein. We now find that patients with acute CMV infection but not those with acute infections from a variety of other nonherpes organisms also produce IgM antibodies that recognize the EBV-derived peptide P62. These antibodies also appear to recognize the same cellular proteins as the EBV-induced IgM antibodies. The IgM antibodies appeared in all acutely infected CMV patients studied and occurred both in patients with previous EBV infections and in one patient studied who had not previously been exposed to EBV. It appears that infection with EBV or CMV can induce the synthesis of a very similar or identical set of IgM antibodies.

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.

A synthetic peptide defines a serologic IgA response to a human papillomavirus-encoded nuclear antigen expressed in virus-carrying cervical neoplasia

The growing awareness of the role of human papillomavirus (HPV) in cervical carcinoma has triggered a search for uncomplicated detection methods. To define a serologic response to HPV, we synthesized peptides based on sequences deduced from the genome of HPV type 16, the most common malignancy-associated type of HPV. One of these peptides reacted with IgA antibodies present in sera from 24 of 33 patients with cervical intraepithelial neoplasia or cervical carcinoma, whereas this peptide reacted with only 6 of 27 sera from individuals without cervical intraepithelial neoplasia. Immunoaffinity-purified human antipeptide IgA antibodies detected HPV-specific 58- and 48-kDa proteins in cervical carcinoma cell extracts and also detected a nuclear antigen in HPV-carrying cervical cancer cell lines and cervical intraepithelial neoplasia biopsied tissue. These antigens were also detected with mouse monoclonal and rabbit polyclonal antibodies to the same peptide. The results indicate that screening for infection with malignancy-associated types of HPV may be possible by simple synthetic peptide-based serology.

Distinction between Epstein-Barr virus type A (EBNA 2A) and type B (EBNA 2B) isolates extends to the EBNA 3 family of nuclear proteins

The Epstein-Barr virus (EBV) nuclear antigens EBNA 3a, 3b, and 3c have recently been mapped to adjacent reading frames in the BamHI L and E fragments of the B95.8 EBV genome. We studied by immunoblotting the expression of the family of EBNA 3 proteins in a panel of 20 EBV-transformed lymphoblastoid cell lines (LCLs) carrying either type A (EBNA 2A-encoding) or type B (EBNA 2B-encoding) virus isolates. Certain human sera from donors naturally infected with type A isolates detected the EBNA 3a, 3b, and 3c proteins in all type A virus-transformed LCLs (with a single exception in which EBNA 3b was not detected) but detected only EBNA 3a in LCLs carrying type B isolates. These results were confirmed with human and murine antibodies with specific reactivity against sequences of the type A EBNA 3a, 3b, or 3c expressed in bacterial fusion proteins. Conversely, selected human sera from donors naturally infected with type B strains of EBV identified the EBNA 3a encoded by both types of isolates plus two novel EBNAs present only in type B, and not in type A, virus-transformed LCLs; these novel proteins appear to be the type B homologs of EBNA 3b and 3c. The distinction between type A and type B EBV isolates therefore extends beyond the EBNA 2 gene to the EBNA 3 family of proteins. This has important implications with respect to the evolutionary origin of these two EBV types and also places in a new light recent studies which identified differences between type A and type B transformants in terms of growth phenotype (A. B. Rickinson, L. S. Young, and M. Rowe, J. Virol. 61:1310-1317, 1987) and of detection by EBV-specific cytotoxic T cells (D. J. Moss, I. S. Misko, S. R. Burrows, K. Burman, R. McCarthy, and T. B. Sculley, Nature [London] 331:719-721, 1988).

EBNA-1: a virally induced nuclear antigen of primate lymphocytes and its expression in Drosophila cells

EBNA-1 is a nuclear antigen of lymphocytes infected by Epstein-Barr virus and whose size polymorphism correlates only with the strain of infecting virus and the length of the glycine-alanine copolymer encoded by the third internal repeat of the viral genome. The major antigenic determinant(s) also appear to reside in this region. We have been able to obtain efficient expression of this nuclear antigen in cultured Drosophila cells transfected with a cosmid carrying the EBNA-1 coding region, indicating that insect mechanisms recognise control sequences and transcripts of the herpes virus. The association of a vimertin-like protein of mol. wt. 46,000 with Drosophila cell nuclei has been found to vary with culture conditions and heat shock. We now find that the level and nuclear association of this protein also increase after transfection with either EBNA-1 or yolk protein DNA.

Purification and characterization of the Epstein-Barr virus nuclear antigen 2 using monoclonal antipeptide antibodies

The Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA-2) is the only one of the EBNA proteins to have been implicated as an EBV-encoded transforming protein. More detailed studies of this protein have been hampered by the lack of EBNA-2-specific monoclonal antibodies (MAbs) and of purified protein. To overcome these problems, we isolated 5 hybridomas producing MAbs reactive with an 18 residue synthetic peptide corresponding to the carboxyterminus of EBNA-2. Four of the 5 MAbs were specifically reactive with EBNA-2 in its denatured form on immunoblots. The 5th antibody (115E) was reactive with the native form of EBNA-2. By using a one-step immunoaffinity purification method with 115E cross-linked to protein-A-Sepharose, we purified EBNA-2 to homogeneity, i.e., more than 1,200-fold, from Burkitt lymphoma cell extracts. A major 32-kDa associated protein and a less abundant 17-kDa protein were co-purified with EBNA-2. Immunoprecipitation with 115E from 35S-methionine-labelled cell extracts showed that the 32-kDa protein co-precipitated with EBNA-2 from EBV-positive cells, but was not detectable in immunoprecipitates of EBV-negative cells. When the immunoprecipitates or the purified proteins were immunoblotted with EBV-immune sera, only EBNA-2 was reactive, indicating that the associated proteins are of cellular origin. Immunoprecipitation of cells labelled with 32P-orthophosphate showed that EBNA-2, but not the associated proteins, is a phosphoprotein. The expression level of EBNA-2 varied between different EBV-carrying cell lines, as measured by a 2-site ELISA based on antibody 115E. In indirect immunofluorescence, the 115E MAb gave an EBNA-2-specific characteristic granular staining pattern. These characteristics of EBNA-2 resemble those of other viral transforming proteins.

Eradication of Epstein-Barr virus by allogeneic bone marrow transplantation: implications for sites of viral latency

Wild-type strains of Epstein-Barr virus (EBV) can be distinguished on the basis of variations in the molecular weight of virus-encoded, growth transformation-associated proteins. This approach was used to study the persistence of EBV in two seropositive recipients of allogeneic bone marrow transplants. The first patient received marrow from her EBV-seronegative brother, became EBV seronegative after grafting, and remained so for greater than 1200 days. Subsequently, she became infected with a new EBV strain that differed from her pretransplant strain but was indistinguishable from the virus isolated from her husband. The second patient received marrow from his EBV-seropositive brother. This patient showed only a transient decrease in IgG antibodies to EBV capsid antigen. His pretransplant strain differed from the virus of his donor. On days 252 and 915 after transplantation, lymphoblastoid cell lines were grown from the peripheral blood of the patient and were found to carry exclusively the virus of the donor. These results suggest that the latently EBV-infected host cells reside in a cellular compartment that can be destroyed by graft-versus-host reactivity, irradiation, or cytotoxic drugs. Hemopoietic tissue is the most likely candidate.

Expression of the Epstein-Barr virus encoded EBNA-1 gene in stably transfected human and murine cell lines

Five murine and 3 human tumor cell lines were transfected with a retroviral vector that carries the EBV encoded EBNA-1 gene. All cell lines expressed intranuclear EBNA-1 as detected by anticomplement immunofluorescence and Western blot assays. The cell lines differed in the level of EBNA-1 expression and the size of the protein. The internal major late promoter of adenovirus was efficient in directing the transcription of EBNA-1 in the human lymphoma line BJAB, the murine T-cell lymphoma Tikaut, RBL-5, EL-4 and in the mouse sarcoma line MSWBS but was less efficient in Ramos, an EBV negative Burkitt lymphoma line, the human T-cell leukemia line 1301TK and the P815-X2 mouse mastocytoma line. All transfected lines except MSWBS contained EBNA-1 in a truncated form. The truncated EBNA-1 polypeptide reacted with the conventional human antibody reagents in an EBNA specific fashion but failed to bind rabbit or human antibody directed against the glycine-alanine repeat sequence. MSWBS contained a truncated as well as a full size EBNA-1 polypeptide. It also reacted with antibody directed against the glycine-alanine repeat. This indicates that the repeat sequence is regularly affected by the truncation.

Expression of Epstein-Barr virus-encoded proteins in nasopharyngeal carcinoma

Expression of the Epstein-Barr virus (EBV) encoded nuclear antigens (EBNA 1 to 6) and membrane-associated protein (LMP) was investigated by immunoblotting in 83 nasopharyngeal carcinoma (NPC) biopsies and 25 other tumor and normal tissue specimens from the head and neck region. Fifty-eight of the 83 NPC biopsies were large enough to yield parallel data on virus DNA and viral expression. All 16 cases of clinically diagnosed and histologically confirmed NPCs from North Africa contained EBV DNA and expressed EBNA-1. Of 31 clinically diagnosed NPCs from China, 29 contained EBV DNA and 25 of these expressed EBNA-1. One control tissue biopsy from the oropharynx of NPC patients contained EBV DNA, but none expressed EBNA-1. The latent membrane protein (LMP) was detected in 22/31 of the Chinese and in 10/16 of the North African NPC biopsies. None of the NPC biopsies or control tissues expressed detectable amounts of EBNA 2 or any of the other 4 nuclear antigens which are invariably expressed in EBV-transformed B cells. A smaller number of tumors from Malaysia and East Africa exhibited a similar pattern of expression. EBV was rescued from a nude-mouse-passaged North African NPC tumor by co-cultivation of the tumor cells with umbilical cord blood lymphocytes. The tumor expressed EBNA 1 and LMP, but not EBNA 2 or the other 4 EBNAs. The resulting LCLs expressed all 6 nuclear antigens, EBNA 1 to 6 and LMP. Our data suggest that expression of the EBV genome is regulated in a tissue-specific fashion.

Proteins in normal and malignant cells, cross-reacting with the latent membrane protein encoded by Epstein-Barr virus

Human B lymphocytes transformed by infection with the Epstein-Barr virus (EBV) express a new membrane protein of 63 kDa (latent membrane protein, LMP) encoded by the virus. The function of this protein in the virus-cell interaction is not known. In this work we have identified in EBV- human and mouse cell molecules which cross-react with LMP. Two types of reagents were employed: (a) antibodies against LMP-derived synthetic peptides, affinity purified from antisera against a fusion protein containing the carboxy half of the LMP molecule and (b) antisera prepared by immunizing rabbits directly with the peptide conjugates. Cross-reactions were determined by radioimmunoblotting experiments. At least six molecules (Mr = 110, 85, 63, 53, 45 and 23 kDa), present in a variety of human cells (peripheral blood lymphocytes, B cell lines and epithelial cell lines) were found to cross-react with the LMP-derived peptides. Cross-reacting proteins were also identified in normal mouse tissues. The specificity of the cross-reacting antibodies was confirmed by inhibition experiments with the corresponding peptide. Furthermore, antibodies eluted from individual bands were shown to bind to the same band when reacted with new blots of the same extracts. Our data suggest that normal cells contain a family of highly conserved proteins cross-reacting with the LMP molecule. If, indeed, these proteins share common functions, their study may lead the way to unraveling the function of LMP.