Identification of Epstein-Barr virus strain differences with monoclonal antibody to a membrane glycoprotein

Purification and quantification of recombinant Epstein-Barr viral glycoproteins gp350/220 from Chinese hamster ovary cells

Truncated Epstein-Barr virus (EBV) membrane antigen gp350/220 (EBV-MA) lacking the membrane anchor was expressed and secreted into the medium of recombinant Chinese hamster ovary cells that had been cultured in Plasmapur hollow-fibre modules using defined serum-free medium. The EBV-MA in the medium was concentrated by 70% (w/v) ammonium sulphate precipitation and subsequently purified by immunoaffinity chromatography using an anti-EBV-MA (EBV.0T6) monoclonal antibody (mAb) column. Adsorbed antigen was eluted with 3 M MgCl2 in phosphate-buffered saline, concentrated by Mono Q anion-exchange chromatography and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, silver staining and Western blotting using EBV-positive serum and anti-EBV-MA specific mAbs. Monospecific polyclonal rabbit antibodies against the purified EBV-MA were raised and purified by protein G affinity chromatography. For the measurement of EBV-MA antigen levels a sandwich enzyme-linked immunosorbent assay using rabbit polyclonal antibodies and a horseradish peroxidase-conjugated anti-MA mAb was developed having a detection level of 10 ng/ml.

Detection of Pediococcus spp. in brewing yeast by a rapid immunoassay

A membrane immunofluorescent-antibody test was developed to detect diacetyl-producing Pediococcus contaminants in brewery pitching yeast (yeast [Saccharomyces cerevisiae] slurry collected for reinoculation). Centrifugations at 11 and 5,100 x g separate yeast cells from bacteria and concentrate the bacteria, respectively. Pelleted bacteria resuspended and trapped on a black membrane filter are reacted with monoclonal antibodies specific for cell surface antigens and then with fluorescein-conjugated indicator antibodies. Whether pitching yeast is contaminated with pediococci at 0.001% is determined in less than 4 h. The sensitivity of the assay is 2 orders of magnitude below the Pediococcus detection limit of direct microscopy.

Three pathways of Epstein-Barr virus gene activation from EBNA1-positive latency in B lymphocytes

Previous studies on Epstein-Barr virus (EBV)-positive B-cell lines have identified two distinct forms of virus latency. Lymphoblastoid cell lines generated by virus-induced transformation of normal B cells in vitro, express the full spectrum of six EBNAs and three latent membrane proteins (LMP1, LMP2A, and LMP2B); furthermore, these lines often contain a small fraction of cells spontaneously entering the lytic cycle. In contrast, Burkitt's lymphoma-derived cell lines retaining the tumor biopsy cell phenotype express only one of the latent proteins, the nuclear antigen EBNA1; such cells do not enter the lytic cycle spontaneously but may be induced to do so by treatment with such agents as tetradecanoyl phorbol acetate and anti-immunoglobulin. The present study set out to determine whether activation of full virus latent-gene expression was a necessary accompaniment to induction of the lytic cycle in Burkitt's lymphoma lines. Detailed analysis of Burkitt's lymphoma lines responding to anti-immunoglobulin treatment revealed three response pathways of EBV gene activation from EBNA1-positive latency. A first, rapid response pathway involves direct entry of cells into the lytic cycle without broadening of the pattern of latent gene expression; thereafter, the three "latent" LMPs are expressed as early lytic cycle antigens. A second, delayed response pathway in another cell subpopulation involves the activation of full latent gene expression and conversion to a lymphoblastoidlike cell phenotype. A third response pathway in yet another subpopulation involves the selective activation of LMPs, with no induction of the lytic cycle and with EBNA expression still restricted to EBNA1; this type of latent infection in B lymphocytes has hitherto not been described. Interestingly, the EBNA1+ LMP+ cells displayed some but not all of the phenotypic changes normally induced by LMP1 expression in a B-cell environment. These studies highlight the existence of four different types of EBV infection in B cells, including three distinct forms of latency, which we now term latency I, latency II, and latency III.

Fluorescent tetradecanoylphorbol acetate: a novel probe of phorbol ester binding domains

Protein kinase C (PKC) has a prominent role in signal transduction of many bioactive substances. We synthesized the fluorescent derivative, phorbol-13-acetate-12-N-methyl-N-4-(N,N'-di(2-hydroxyethyl)amino)-7-n itr obenz-2-oxa-1,3-diazole-aminododecanoate (N-C12-Ac(13)) of 12-O-tetradecanoylphorbol-13-acetate (TPA) to monitor the location of phorbol ester binding sites and evaluate its potential use as a probe of PKC in viable cells. The excitation maximum wavelength of N-C12-Ac(13) is close to 488 nm, facilitating its use in argon-ion laser flow and imaging cytometry. When incubated with 100 nM N-C12-Ac(13) at 25 degrees C, P3HR-1 Burkitt lymphoma cells accumulated the dye rapidly, reaching maximum fluorescence within 25 min, 20-fold above autofluorescence. Addition of unlabeled TPA significantly decreased the fluorescence of N-C12-Ac(13) stained cells in a dose-dependent manner indicating specific displacement of the bound fluoroprobe. Competitive displacement of [3H]-phorbol-12,13-dibutyrate ([3H]-PBu2) from rat brain cytosol with N-C12-Ac(13) gave an apparent dissociation constant (Kd) of 11 nM. N-C12-Ac(13) possessed biological activity similar to TPA. Like TPA (final concentration 65 nM) N-C12-Ac(13), at a lower concentration (51 nM), induced expression of Epstein-Barr viral glycoprotein in P3HR-1 cells, differentiation of promyelocytic HL60 cells, and caused predicted changes in the mitotic cycle of histiocytic DD cells. Microspectrofluorometric images of single cells labeled with N-C12-Ac(13) showed bright fluorescence localized intracellularly and dim fluorescence in the nuclear region, consistent with dye binding mainly to cytoplasmic structures and/or organelles and being mostly excluded from the nucleus. Because of the high level of non-specific binding of N-C12-Ac(13), this probe is not ideal for visualizing PKC in intact cells, but would be a valuable fluoroprobe to investigate the kinetic properties of purified PKC. Also, knowledge gained from these studies allows us to predict structures of fluorescent phorbols likely to have less non-specific binding and, consequently, be potentially useful for monitoring PKC in viable cells.

Epstein-Barr virus (EBV) glycoprotein gp350 expressed on transfected cells resistant to natural killer cell activity serves as a target antigen for EBV-specific antibody-dependent cellular cytotoxicity

Cell surface-associated viral glycoproteins are thought to play a major role as target antigens in cellular cytotoxicity and antiviral immunosurveillance. One such glycoprotein is the Epstein-Barr virus (EBV)-encoded glycoprotein 350 (gp350), which is expressed on both virion envelope and EBV producer cells and carries the virus attachment protein moiety. Although it is known that some antibodies to gp350 can neutralize the virus, the role of this glycoprotein in EBV-specific cellular cytotoxicity is not yet clear. We describe here a study in which we successfully used a new approach to demonstrate that gp350 is a target antigen for EBV-specific antibody-dependent cellular cytotoxicity (ADCC). Transfection of gp350-negative cells resistant to natural killer (NK) cell activity (i.e., Raji) with a recombinant vector (pZIP-MA) containing the gene encoding the EBV-gp350 and the neomycin resistance gene enabled us to isolate cell clones with a stable and strong expression of gp350 on their surface membranes. ADCC determined by using two clones clearly demonstrated that gp350 is the target of the EBV ADCC. Interestingly, this ADCC was comparable to that obtained against the EBV-superinfected (coated) Raji cell expressing the same percentage of gp350 positivity as the two clones. No cytotoxic activity was detected against either nontransfected (gp350-negative) Raji cells or cells transfected with the vector [pZIP-neo-SV(X)1] lacking the gp350 gene. In addition to demonstrating that gp350 is a target molecule for EBV-specific ADCC, our approach in using NK-resistant transfectants provides a lead for probing the role of cell surface-associated viral antigens in specific cellular killing and immunosurveillance.

Development of an enzyme-linked immunosorbent assay (ELISA) for detecting IgA antibodies to the Epstein-Barr virus

A 3-step enzyme-linked immunosorbent assay (ELISA) was developed for detecting IgA antibodies to purified Epstein-Barr virus (EBV) polypeptides. The 3-step procedure included the use of a mouse anti-human IgA monoclonal antibody (MAb) to amplify the IgA reaction. The 2 major EBV proteins used in this assay were the 125-kDa component (gp125) associated with the viral capsid antigen (VCA) complex and a major glycoprotein (gp250/200) associated with the membrane antigen (MA) complex. Eighty-two sera were tested on ELISA plates containing either both of the glycoproteins or each one separately. These included 45 IgA antibody-positive sera from patients with nasopharyngeal carcinoma (NPC). With these sera, there was a good correlation, both qualitatively and quantitatively, between results with the immunofluorescence (IF) and ELISA procedures. Although most IgA antibody-positive sera contained antibodies reactive with both gp125 and gp250/200, a number of sera contained antibodies reactive with one of the glycoproteins but not with both. The data indicated that both of these glycoproteins should be used in assays for detecting IgA antibodies to EBV, to avoid false-negative results. This assay should be useful for screening large populations for IgA antibodies to EBV and also possibly for monitoring disease course in patients with NPC.

Identification of the Epstein-Barr virus gp85 gene

The Epstein-Barr virus glycoprotein gp85 has been mapped to the Epstein-Barr virus DNA open reading frame BXLF2 (R. Baer, A. Bankier, M. Biggin, P. Deininger, P. Farrell, T. Gibson, G. Hatfull, G. Hudson, S. Stachwell, C. Sequin, P. Tufnell, and B. Barrell, Nature [London] 310:207-211, 1984). A gp85-specific monoclonal antibody reacts with the BXLF2 in vitro transcription-translation product. The monoclonal antibody also precipitates an 85-kilodalton protein from rodent cells transfected with the BXLF2 open reading frame DNA. In these cells, gp85 localizes to the cytoplasm and nuclear rim rather than to the plasma membrane as in lymphocytes. Northern (RNA) blot hybridization and analysis of a cDNA clone containing BXLF2 indicate that gp85 is translated from an unspliced, late, 2.5-kilobase transcript. Similarities between the predicted amino acid sequences of gp85 and herpes simplex virus gH (D. McGeoch and A. Davison, Nucleic Acids Res. 14:4281-4292, 1986) are noted.

A neutralizing monoclonal antibody recognizes an 87K envelope glycoprotein on the murine cytomegalovirus virion

An 87K glycoprotein (gp87) on the murine cytomegalovirus (MCMV) virion was immunoprecipitated by the neutralizing monoclonal antibody (MAb) 8D1.11A. The 87K glycoprotein is also radiolabeled in a surface iodination reaction, suggesting that it is exposed on the surface of the virion. Using a nondenaturing system of polyacrylamide gel electrophoresis in combination with Western blotting, we have shown that the epitope recognized by the MAb 8D1.11A resides on gp87. The failure of 8D1.11A to react with gp87 in a reduced and denatured form suggests that the epitope is recognized only when disulfide linkages are preserved. Our data also indicated that gp87 is present in the MCMV virion both in a monomeric form and as a component of disulfide-linked complexes. Using a two-dimensional gel electrophoresis system, we have demonstrated the presence of disulfide linkages between gp87 and virion polypeptides with apparent molecular weights of 138K, 46K, and 20K. Finally, the difference in migration rates of gp87 in SDS-polyacrylamide gels under reducing and nonreducing conditions suggests the existence of intramolecular disulfide bonds.

HTLV-III infection of EBV-genome-positive B-lymphoid cells with or without detectable T4 antigens

The infection of a number of new and established B-cell lines by human T-cell lymphotropic virus III (HTLV-III) was investigated. The B lymphocytes differed in their expression of T4 antigens detected by specific monoclonal antibodies (MAbs) and the presence of Epstein Barr virus (EBV)-DNA or antigens. The presence of the EBV genome was the only requirement for infection of B-lymphocytes by HTLV-III, although its presence did not ensure infection. Two EBV genome and T4 antigen-positive B-cell lines, lacking EBV early antigens (EA) and viral capsid antigens (VCA), could be productively infected with no induction of known EBV antigens. Two other EBV genome-positive cell lines, lacking T4, EA, and VCA could also be infected. Another genome-positive cell line (P3HR-I) that was EBV-EA, VCA-positive and produced non-transforming EBV, could also be infected by HTLV-III. However, 3 EBV genome- and T4 antigen-negative B-cell lines could only be infected with HTLV-III after successful conversion to an EBV-genome-positive state by pre-infection with EBV. Five other EBV-genome-positive B-cell lines lacking T4 antigens were not infectible with HTLV-III even after super-infection with EBV. Incomplete inhibition of the HTLV-III infection of a T4-positive (LDV-7) and a T4-negative (Craig) was obtained by preadsorption with specific MAb to T4 (OKT4A and Leu 3A). From these observations, it is not clear whether the presence of T4 antigen on the cell surface is needed for the infection of B lymphoblastoid cells; however, successful infection does depend upon the presence of the EBV genome. The mechanism of interaction of HTLV-III and EBV-infected B-cell lines permitting this infection is not fully understood. Although the clinical implications of these observations remain to be determined, it is possible that infection of EBV-positive B-cells may contribute to aberrant humoral responses and/or increased frequency of B-cell malignancies observed in HTLV-III-infected individuals.

Two major outer envelope glycoproteins of Epstein-Barr virus are encoded by the same gene

Two major outer envelope glycoproteins of Epstein-Barr virus, gp350 and gp220, are known to be encoded by 3.2- and 2.5-kilobase RNAs which map to the same DNA fragment (M. Hummel, D. Thorley-Lawson, and E. Kieff, J. Virol. 49:413-417). These RNAs have the same 5' and 3' ends. The larger RNA is encoded by a 2,777-base DNA segment which is preceded by TATTAAA, has AATAAA near its 3' end, and contains a 2,721-base open reading frame. The smaller RNA has one internal splice which maintains the same open reading frame. Translation of the 3.2- and 2.5-kilobase RNAs yielded proteins of 135 and 100 kilodaltons (Hummel et al., J. Virol. 49:413-417). The discrepancy between the 907 codons of the open reading frame and the 135-kilodalton size of the gp350 precursor is due to anomalous behavior of the protein in gel electrophoresis, since a protein translated from most of the Epstein-Barr virus open reading frame in Escherichia coli had similar properties. Antisera raised in rabbits to the protein expressed in E. coli specifically immunoprecipitated gp350 and gp220, confirming the mapping and sequencing results and the translational reading frame. The rabbit antisera also reacted with the plasma membranes of cells that were replicating virus and neutralized virus, particularly after the addition of complement. This is the first demonstration that the primary amino acid sequence of gp350 and gp220 has epitopes which can induce neutralizing antibody. We propose a model for the gp350 protein based on the theoretical analysis of its primary sequence.

Inhibition of Epstein-Barr virus (EBV) release from the P3HR-1 Burkitt's lymphoma cell line by a monoclonal antibody against a 200,000 dalton EBV membrane antigen

In raising murine hybridoma antibodies against Epstein-Barr virus (EBV)-induced membrane antigens (MA), we found one antibody that blocked the release of infectious EBV from cultured P3HR-1 cells. This monoclonal antibody (mAb) recognized a 200 kD, phosphonoacetic acid-sensitive (late) MA, and did not directly neutralize virus without complement. When this mAb was added to 33 degrees C-cultured, spontaneously EBV-producing P3HR-1 cells, the intracellular expression of viral capsid antigen and infectious virus was not inhibited, but the appearance of infectious virus in the culture medium was significantly reduced. The duration of this suppression was dependent upon the concentration of the mAb, an effect being observed to a 1:4 X 10(5) titer of the ascites mAb preparation. A more acute effect of suppression of EBV release was observed in a second model of 12-o-tetradecanoyl phorbol-13-acetate and n-butyrate induction of EBV in 37 degrees C-cultured P3HR-1 cells. Again, intracellular infectious virus production was not inhibited, but the level of infectious virus in the culture medium was significantly reduced as early as 1 and 2 d of culture with antibody. This effect was reversed within 31 h after replacement of mAb-containing medium with fresh medium. This description of antibody-mediated inhibition of EBV release might lead to the characterization of another form of immune defense for the control of EBV infections.

Characterization of a major protein with a molecular weight of 160,000 associated with the viral capsid of Epstein-Barr virus

A monoclonal antibody designated V3 was produced against a late protein associated with the Epstein-Barr virus-induced viral capsid antigen complex. The antibody reacted with discrete patches in the nuclei of infected cells as well as with virus particles, as shown by immunofluorescence and ultrastructural immunoperoxidase staining. The molecular weight of the protein precipitated by this monoclonal antibody was ca. 160,000. All anti-viral capsid antigen antibody-positive sera tested in an enzyme-linked immunosorbent assay reacted with this purified protein. The synthesis of the antigen was inhibited by phosphonoacetic acid but was not affected by tunicamycin, indicating that this was a late nonglycosylated viral protein. No differences were noted between the protein isolated from the P3HR-1 and B-95-8 cell lines as determined by immunoprecipitation and peptide mapping. By isoelectric focusing, this protein had a pI on the basic side ranging from 7.5 to 9.0.

Identification and characterization of a cellular protein that cross-reacts with the Epstein-Barr virus nuclear antigen

A 62,000-dalton (62K) cell protein reacts with antisera to the 72K polypeptide of the Epstein-Barr virus nuclear antigen (EBNA) in immunoblots. This protein was initially detected in EBNA-negative as well as EBNA-positive cell lines with anti-EBNA-positive human sera. A monoclonal antibody raised against the 72K EBNA and an antiserum from a rabbit immunized with the glycine-alanine domain of EBNA also reacted with the cellular protein. The cellular protein was partially purified from Epstein-Barr virus genome-positive and -negative cell lines. Absorption experiments identified a shared antigenic determinant between the 72K EBNA and 62K cellular protein. A comparison of the 62K protein and EBNA by protease digestion did not reveal similar peptides.

An Epstein-Barr virus DNA fragment encodes messages for the two major envelope glycoproteins (gp350/300 and gp220/200)

The genes encoding the two major Epstein-Barr virus glycoproteins (gp350/300 and gp220/200) have been mapped to a 5-kilobase fragment of the viral genome (BamHI-L). This fragment encodes 3.4- and 2.8-kilobase RNAs which translate proteins of 135 and 100 kilodaltons, respectively. Both proteins react with antiserum specific for gp350/300 and gp220/200. The 135-kilodalton protein is identical in size to the nascent polypeptide precursor to gp350/300, and the 100-kilodalton protein is the expected size of the polypeptide precursor to gp220/200.

The application of monoclonal antibodies in the study of viruses

This chapter discusses the applications of monoclonal antibodies in virology. A single monoclonal antibody can provide information on protein “relatedness,” structure, function, synthesis, processing, and cellular or tissue distribution and on the association among molecules. The use of monoclonal antibodies provides valuable insight into the working of the protein both as an enzyme and as a target for the host immune response, evolving in reaction to that response. Monoclonal antibodies find application in two main areas: (1) in the field of rapid diagnosis of virus disease in man, animals, and plants and (2) in the extension of virus taxonomy. Monoclonal antibodies may be used to analyze the role of a protein. This ability to distinguish related proteins can be used to provide a genetic marker in recombination experiments. Monoclonal antibodies can detect low amounts of individual virus proteins within the infected cell. They can, thus, provide information concerning the temporal and spatial separation of protein formation and accumulation, and data on protein modification and processing in the infected cell.

Identification of polypeptide components of the Epstein-Barr virus early antigen complex with monoclonal antibodies

Three monoclonal antibodies were produced against the Epstein-Barr virus-induced early antigen complex. These antibodies were shown to be specific for the early antigen complex by the fact that they only reacted with cells supporting a permissive or abortive Epstein-Barr virus infection and their synthesis was not affected by inhibitors of viral DNA synthesis. One monoclonal antibody, designated R3, was directed against a diffuse component of the early antigen complex since it reacted by immunofluorescence with cells fixed in acetone or methanol. The other two monoclonal antibodies, designated K8 and K9, reacted with a methanol-sensitive restricted component of this complex. The appearance of the R3 antigen in P3HR-1 superinfected Raji cells occurred approximately 4 h earlier than the antigen detected by K8. By both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and radioimmunoelectrophoresis, it was determined that the R3 monoclonal antibody recognized two major polypeptides with molecular weights of approximately 50,000 to 52,000, whereas K8 and K9 precipitated a protein of approximately 85,000. The R3 monoclonal antibody also immunoprecipitated an in vitro primary translation product. It was, therefore, possible to map this product to the Epstein-Barr virus DNA BamH1 M fragment. These in vitro products were slightly smaller than the in vivo proteins, suggesting that these proteins probably undergo posttranslational modification during the virus replication cycle.

Monoclonal antibody specific for capsid antigen of Epstein-Barr virus

A hybrid cell line (Cl-51) producing an anti-capsid antibody was obtained by fusion of mouse myeloma cells with spleen cells from mice immunized with purified P3HR-1 Epstein-Barr virus (EBV). Immunofluorescence showed that the Cl-51 antibody reacted with the cytoplasm and the nucleus of P3HR-1 and B95-8 cells, but not with Raji, BJAB, Molt-4, and superinfected Raji cells in the presence of cytosine arabinoside (Ara-C). The viable P3HR-1 and B95-8 cells were not stained nor was the viral infectivity neutralized. The Cl-51 antibody immunoprecipitated 123,000 and 120,000 dalton polypeptides of P3HR-1 and B95-8 cells, respectively, and both were sensitive to phosphonoacetic acid. Specific reactions were not evident with extracts of Raji cells and superinfected Raji cells in the presence of Ara-C. An analysis of the purified virus particles showed that this antibody recognized a capsid component of EBV.

Purified Epstein-Barr virus Mr 340,000 glycoprotein induces potent virus-neutralizing antibodies when incorporated in liposomes

The purified Mr 340,000 glycoprotein component of Epstein-Barr (EB) virus-induced membrane antigen complex incorporated into liposomes was shown to be a potent immunogen in mice. High-titer antisera were induced that (i) are specific for membrane antigen components without absorption, (ii) bind the antigens induced by three different EB virus isolates, and (iii) neutralize the ability of the virus to transform fetal cord blood lymphocytes in vitro. The development of this immunogenic form of purified antigen provides an important step towards a potential subunit vaccine against Epstein-Barr virus infection.

Membrane antigen on Epstein--Barr virus-infected human B cells recognized by a monoclonal antibody

This paper describes a monoclonal antibody (B532) that detects a membrane antigen present on greater than or equal to 95% of the B cells from lines carrying the Epstein-Barr virus (EBV) genome. Evidence suggesting that B532 is EBV-related was originally obtained by using a cell-binding radioassay with different cell line substrates. Immunofluorescence and cell-sorter analysis confirmed that the antigen was present in high density on all EBV-infected lymphoblastoid B-cell lines, but not on EBV-negative B-, T-, myeloid, or null cell lines. Isolated normal peripheral blood B and T lymphocytes and monocytes failed to bind B532. The monoclonal antibody did not inhibit in vitro EVB infection nor did it block the killing of EBV-infected targets by cytotoxic T lymphocytes. The cell surface antigen recognized by B532 was shown by immunoprecipitation to have a molecular weight of approximately 45,000.