The type-specific epitopes of the Epstein-Barr virus nuclear antigen 2 are near the carboxy terminus of the protein

Epstein-Barr virus and cancer

EBV was the first human virus to be directly implicated in carcinogenesis. It infects >90% of the world's population. Although most humans coexist with the virus without serious sequelae, a small proportion will develop tumors. Normal host populations can have vastly different susceptibility to EBV-related tumors as demonstrated by geographical and immunological variations in the prevalence of these cancers. EBV has been implicated in the pathogenesis of Burkitt's lymphoma, Hodgkin's disease, non-Hodgkin's lymphoma, nasopharyngeal carcinoma, and lymphomas, as well as leiomyosarcomas arising in immunocompromised individuals. The presence of this virus has also been associated with epithelial malignancies arising in the gastric region and the breast, although some of this work remains in dispute. EBV uses its viral proteins, the actions of which mimic several growth factors, transcription factors, and antiapoptotic factors, to usurp control of the cellular pathways that regulate diverse homeostatic cellular functions. Recent advances in antiviral therapeutics, application of monoclonal antibodies, and generation of EBV-specific CTLs are beginning to show promise in the treatment of EBV-related disorders.

Epstein-Barr virus recombinants from BC-1 and BC-2 can immortalize human primary B lymphocytes with different levels of efficiency and in the absence of coinfection by Kaposi's sarcoma-associated herpesvirus

Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) are human gammaherpesviruses associated with numerous malignancies. Primary effusion lymphoma or body cavity-based lymphoma is a distinct clinicopathological entity that, in the majority of cases, manifests coinfection with KSHV and EBV. In previous analyses, we have characterized the EBV in the BC-1 and BC-2 cell lines as potential intertypic recombinants of the EBV types 1 and 2. In order to examine the infectious and transforming capacities of KSHV and the intertypic EBV recombinants from the BC-1 and BC-2 cell lines, viral replication was induced in these cell lines and fresh human primary B lymphocytes were infected with progeny virus. The transformed clones were analyzed by PCR and Western blotting. All analyzed clones were infected with the intertypic progeny EBV but had no detectable signal for progeny KSHV. Additionally, primary B lymphocytes incubated with viral supernatant containing KSHV alone showed an unsustained initial proliferation, but prolonged growth or immortalization of these cells in vitro was not observed. We also show that the EBV recombinants from BC-1 were less efficient than the EBV recombinants from BC-2 in the ability to maintain the transformed phenotype of the infected human B lymphocytes. From these findings, we conclude that the BC-1 and BC-2 intertypic EBV recombinants can immortalize human primary B lymphocytes, albeit at different levels of efficiency. However, the KSHV induced from BC-1 and BC-2 alone cannot transform primary B cells, nor can it coinfect EBV-positive B lymphocytes under our experimental conditions with B lymphocytes from EBV-seropositive individuals. These results are distinct from those in one previous report and suggest a possible requirement for other factors to establish coinfection with both viral agents.

Characterization of intertypic recombinants of the Epstein-Barr virus from the body-cavity-based lymphomas cell lines BC-1 and BC-2

Epstein-Barr Virus (EBV) can infect and transform human B-lymphocytes and has been associated with numerous human malignancies. Two distinct types of EBV have been described, EBV-1 and EBV-2. Whereas type 1 is known to be most widespread throughout the healthy adult population, type 2 EBV has been shown to be significantly present in certain T-cell immunocompromised patients. Some evidence also suggests that such immune impairment promotes coinfection with multiple strains of EBV and fosters the development of intertypic recombinant viruses. In this work, we have analyzed two established body-cavity-based lymphoma or primary effusion lymphoma cell lines, BC-1 and BC-2, for the presence of intertypic EBV recombinants. Using PCR primers to amplify across several markers in the genome, we have typed the BC-1 and BC-2 EBV at these loci. Immunoblot analysis of the EBNA1 protein expressed by these cell lines also suggests a change in EBV typing at this locus in these genomes. Additionally, we have analyzed the expression patterns of the latent EBNA proteins from these viruses and performed Southern blot analysis of the BamHI- and EcoRI-digested genomes to detect variations occurring from type I and II genomes. On the basis of these data, we suggest that the genomes of EBV in BC-1 and BC-2 are intertypic recombinants of type 1 and type 2 EBV genomes. This work corroborates other reports that intertypic EBV recombinants occur in the immunocompromised population. It is likely that intertypic recombination is a mechanism by which novel variants of EBV emerge having selective advantages over a strictly type 1 or type 2 strain.

Development of a recombinant enzyme-linked immunosorbent assay for detection of antibodies against Epstein-Barr virus nuclear antigens 2A and 2B

The baculovirus expression system was used to produce full-length Epstein-Barr virus nuclear antigens (EBNAs) 2A and 2B. Recombinant baculoviruses that contained the EBNA-2A- and EBNA-2B-encoding sequences were constructed. The proteins were expressed in Spodoptera frugiperda SF-9 cells infected with the recombinant viruses and were characterized by using monoclonal and human polyclonal antibodies by immunoblotting and immunofluorescence techniques. Partially purified extracts of the EBNA-2A- and EBNA-2B-infected insect cells were used to establish a new enzyme-linked immunosorbent assay for the detection of antibodies against EBNA-2A and EBNA-2B. Preferential reactivity toward the type A or type B EBNA-2 protein was observed in 36% of serum specimens from Swiss patients with acute infectious mononucleosis and in 81% of Swiss patients with latent Epstein-Barr virus infection. Of the patients in the latter group, sera from 76% reacted preferentially with EBNA-2A, sera from 5% reacted preferentially with EBNA-2B, sera from 12% showed similar reactivities against both antigens, and sera from 7% were nonreactive.

Expression of Epstein-Barr virus nuclear antigen 1,2A and 2B in the baculovirus expression system: serological evaluation of human antibodies to these proteins

The Epstein-Barr virus encoded nuclear antigens 1,2A, and 2B (EBNA 1, EBNA 2A, and EBNA 2B) were expressed in a baculovirus system. The full length recombinant proteins were recognized by polyclonal rabbit sera and by human sera. An immunofluorescence (IF) test for the differentiation between EBNA 1 and EBNA 2 antibodies in human sera was established with the expressed proteins. None of 55 sera of patients with infectious mononucleosis (IM) had anti-EBNA 1 antibodies while 36 of these sera had anti-EBNA 2A antibodies. Conversely, 47 of 51 sera from EBV-positive healthy carriers had anti-EBNA 1 antibodies and 18 of these sera had anti-EBNA 2A antibodies. The sensitivity and specificity of the EBNA 1 IF for the diagnosis of IM were higher as compared to conventional anti-complement immunofluorescence (ACIF). In the IF test differentiation between type A and type B EBV infection was only possible in sera from the IM patients. An immunoblot (IB) with low amounts of baculovirus expressed EBNA 2A and EBNA 2B antigen was carried out. Twenty-nine of 31 sera from IM patients or from healthy carriers with EBNA 2 antibodies reacted predominantly with EBNA 2A, whereas a known type B serum reacted strongly with EBNA 2B than with EBNA 2A.

Identification of the Epstein-Barr virus terminal protein gene products in latently infected lymphocytes

The terminal protein (TP) gene produces two overlapping mRNAs in latently infected lymphocytes that are predicted to encode the similar polypeptides TP1 (497 amino acids) and TP2 (378 amino acids), with TP1 exon 1 providing 119 extra unique residues at the N terminus. Rabbit antisera were raised to procaryotic fusion proteins and used to detect expression of a predicted 53-kilodalton (kDa) TP product in transfected 293 cells and latently infected lymphocytes. Fractionation of transfected 293 cells showed this protein to be localized to an integral membrane preparation. The same fraction of latently infected lymphocytes contained proteins of 53 and 27 to 39 kDa as determined by Western immunoblotting with the TP-specific rabbit antisera. Immunoprecipitation of TP products from 35S-labeled human lymphoblastoid cells (CR/B95-8) was used in pulse-chase experiments and showed that TP1 was a labile protein with a half-life of approximately 2 to 4 h. The anti-fusion protein serum detected a 53-kDa TP1 and degradation products in the range of 25 to 35 kDa. A panel of Burkitt's lymphoma cell lines and cell lines established with virus recovered from the BL cells were analyzed by Western immunoblotting and found to contain the 53-kDa TP1 product, its degradation products, or both. Only two EBV-positive BL cell lines (BL72 and Wewak II) were negative in this assay. The results suggest that a labile TP1 protein may be expressed by most, if not all, EBV-infected cell lines.

Mapping of viral epitopes with prokaryotic expression products

Several systems are available for the expression of foreign gene sequences in Escherichia coli. We describe the use of prokaryotic expression products of viral gene fragments in order to identify the regions that specify the binding sites of antibodies. This approach is particularly successful if the antigenicity does not depend on the native protein, but only on the amino acid sequence, i.e., if the epitope is sequential. Combining prokaryotic expression with the use of synthetic peptides often permits a fast and accurate mapping of an epitope. The occurrence of immunodominant sequential epitopes on the surfaces of viruses seems to be a widespread phenomenon.