Identification of an Epstein-Barr virus glycoprotein which is antigenically homologous to the varicella-zoster virus glycoprotein II and the herpes simplex virus glycoprotein B

Mapping regions of Epstein-Barr virus (EBV) glycoprotein B (gB) important for fusion function with gH/gL

Glycoproteins gB and gH/gL are required for entry of Epstein-Barr virus (EBV) into cells, but the role of each glycoprotein and how they function together to mediate fusion is unclear. Analysis of the functional homology of gB from the closely related primate gammaherpesvirus, rhesus lymphocryptovirus (Rh-LCV), showed that EBV gB could not complement Rh gB due to a species-specific dependence between gB and gL. To map domains of gB required for this interaction, we constructed a panel of EBV/Rh gB chimeric proteins. Analysis showed that insertion of Rh gB from residues 456 to 807 restored fusion function of EBV gB with Rh gH/gL, suggesting this region of gB is important for interaction with gH/gL. Split YFP bimolecular complementation (BiFC) provided evidence of an interaction between EBV gB and gH/gL. Together, our results suggest the importance of a gB-gH/gL interaction in EBV-mediated fusion with B cells requiring the region of EBV gB from 456 to 807.

Cleavage of Epstein-Barr virus glycoprotein B is required for full function in cell-cell fusion with both epithelial and B cells

Glycoprotein B (gB) homologues within the herpesvirus family display high sequence conservation, and a number of gB homologues contain a cleavage motif R-X-K/R-R recognized by the cellular protease furin. Epstein-Barr virus (EBV) gB contains this motif and cleaved gB is found in EBV virions. To determine the functional significance of this cleavage motif in EBV gB, a deletion mutant (gB Deltafurin) was created lacking the motif. This cleavage mutant was expressed well in cell culture but was not cleaved. Experiments examining gB Deltafurin in a cell-fusion assay revealed that fusion was reduced by 52 % in epithelial and 28 % in B cells when compared with wild-type EBV gB. This decrease in cell-cell fusion is similar to that observed with multiple alphaherpesvirus gB cleavage mutants and supports a conserved function for cleaved gB.

Primary B-cell infection with a deltaBALF4 Epstein-Barr virus comes to a halt in the endosomal compartment yet still elicits a potent CD4-positive cytotoxic T-cell response

Epstein-Barr virus (EBV) infection is mediated by several viral envelope glycoproteins. We have assessed gp110's functions during the virus life cycle using a mutant that lacks BALF4 (DeltaBALF4). Exposure of various cell lines and primary cell samples of epithelial or lymphoid lineages to the DeltaBALF4 mutant failed to establish stable infections. The DeltaBALF4 virus, however, did not differ from wild-type EBV in its ability to bind and become internalized into primary B cells, in which it elicited a potent T-cell-specific immune reaction against virion constituents. These findings show that DeltaBALF4 viruses can reach the endosome-lysosome compartment and dovetail nicely with the previously identified contribution of gp110 to virus-cell fusion. Other essential steps of the virus life cycle were unaffected in the viral mutant; DNA lytic replication and viral titers were not altered in the absence of gp110, and DeltaBALF4 viruses complemented in trans transformed infected B cells with an efficiency indistinguishable from that observed with wild-type viruses. All of the steps of virus maturation could be observed in lytically induced 293/DeltaBALF4 cells. Induction of lymphoblastoid cells generated with transiently complemented DeltaBALF4 virus led to the production of rare mature virions. We therefore infer that gp110 is not required for virus maturation and egress in 293 cells or in B cells. The DeltaBALF4 virus's phenotypic traits, an inability to infect human cells coupled with potent antigenicity, potentially qualify this mutant as a live vaccine. It will provide a useful tool for the detailed study of EBV-cell interactions in a physiological context.

Analysis of Epstein-Barr virus glycoprotein B functional domains via linker insertion mutagenesis

Epstein-Barr Virus (EBV) glycoprotein B (gB) is essential for viral fusion events with epithelial and B cells. This glycoprotein has been studied extensively in other herpesvirus family members, but functional domains outside of the cytoplasmic tail have not been characterized in EBV gB. In this study, a total of 28 linker insertion mutations were generated throughout the length of gB. In general, the linker insertions did not disrupt intracellular expression and variably altered cell surface expression. Oligomerization was disrupted by insertions located between residues 561 and 620, indicating the location of a potential site of oligomer contacts between EBV gB monomers. In addition, a novel N-glycosylated form of wild-type gB was identified under nonreducing Western blot conditions that likely represents a mature form of the protein. Fusion activity was abolished in all but three variants containing mutations in the N-terminal region (gB30), within the ectodomain (gB421), and in the intracellular C-terminal domain (gB832) of the protein. Fusion activity with variants gB421 and gB832 was comparable to that of the wild type with epithelial and B cells, and only these two mutants, but not gB30, were able to complement gB-null virus and subsequently function in virus entry. The mutant gB30 exhibited a low level of fusion activity with B cells and was unable to complement gB-null virus. The mutations generated here indicate important structural domains, as well as regions important for function in fusion, within EBV gB.

Use of baculovirus-expressed glycoprotein H in an enzyme-linked immunosorbent assay developed to assess exposure to chelonid fibropapillomatosis-associated herpesvirus and its relationship to the prevalence of fibropapillomatosis in sea turtles

Chelonid fibropapillomatosis-associated herpesvirus (CFPHV) is an alphaherpesvirus believed to cause marine turtle fibropapillomatosis (FP). A serodiagnostic assay was developed for monitoring sea turtle populations for CFPHV exposure. CFPHV glycoprotein H (gH) expressed in recombinant baculovirus was used in an enzyme-linked immunosorbent assay (ELISA) to detect virus-specific 7S turtle antibodies. Using captive-reared green turtles (Chelonia mydas) with no history of virus exposure as "known negatives" and others with experimentally induced FP as "known positives," the assay had 100% specificity but low sensitivity, as seroconversion was detected in only half of the turtles bearing experimentally induced tumors. Antibodies were detected only in samples collected after cutaneous fibropapillomas appeared, consistent with observations that tumors are significant sites of virion production and antigen expression and the possibility that prolonged/repeated virus shedding may be required for adequate stimulation of 7S antibody responses to gH. Natural routes of infection, however, may produce higher seroconversion rates. High gH antibody seroprevalences ( approximately 80%) were found among wild green turtles in three Florida localities with different FP prevalences, including one site with no history of FP. In addition, all eight loggerhead turtles (Caretta caretta) tested were seropositive despite FP being uncommon in this species. The possibility that CFPHV infection may be common relative to disease suggests roles for environmental and host factors as modulators of disease expression. Alternatively, the possibility of other antigenically similar herpesviruses present in wild populations cannot be excluded, although antibody cross-reactivity with the lung/eye/trachea disease-associated herpesvirus was ruled out in this study.

Cell-surface expression of a mutated Epstein-Barr virus glycoprotein B allows fusion independent of other viral proteins

Epstein-Barr virus (EBV) infects human B lymphocytes and epithelial cells. We have compared the requirements for EBV glycoprotein-induced cell fusion between Chinese hamster ovary effecter cells and human B lymphoblasts or epithelial cells by using a virus-free cell fusion assay. EBV-encoded gB, gH, gL, and gp42 glycoproteins were required for efficient B cell fusion, whereas EBV gB, gH, and gL glycoproteins were required for Chinese hamster ovary effecter cell fusion with epithelial cell lines (AGS and SCC68) or the human embryonic kidney cell line 293-P. Fusion with human embryonic kidney 293-P cells was greater than fusion observed with B cells, indicative of an important role for cell contact. An antibody directed against the gH and gL complex inhibited epithelial cell fusion. Increased surface expression of gB alone as a result of truncations or point mutants in the carboxyl-terminal tail allowed gB-mediated fusion with epithelial cells, albeit at a lower level than with coexpression of gB, gH, and gL. Overall, gB appears to be the critical component for EBV glycoprotein-mediated cell fusion.

Effect of tandem rare codon substitution and vector-host combinations on the expression of the EBV gp110 C-terminal domain in Escherichia coli

Gp110 of Epstein-Barr virus (EBV) is a glycoprotein that functions exclusively during the assembly of EBV nucleocapsid and the release of infectious EBV. Its C-terminal tail domain (gp110 CTD) is essential for gp110's function and may provide signals that are responsible for the assembly and release of EBV. In the present study, to get large amounts of gp110 CTD for structural analysis, the effects of vector system, codon usage, and host strain on expression levels of gp110 CTD in Escherichia coli have been investigated. The coding region of gp110 CTD (11 kDa) was subcloned into the expression vectors pSE 280, pET-15b, pET-29a, pMAL-c2x, and pGEX-4T-1. Except the pMAL-c2x construct, all the others failed to express detectable amounts of recombinant gp110 CTD. Substituting a tandem rare AGA (Arg) codon with a synonymous CGC (Arg) codon facilitated expression of the recombinant protein, while a protease-deficient host E. coli strain helped in the accumulation of a soluble form of gp110 CTD fusion. The secondary structures of the obtained recombinant gp110 CTD purified from soluble extracts and inclusion bodies were compared using circular dichroism analysis. In aqueous solutions, both samples equally adopt a mixed alpha-helix and beta-sheet conformation as well as a partly unordered structure. Notably, in the membrane-mimicking environments the helical propensity of gp110 CTD increased up to the previously predicted level based on its sequence, suggesting that gp110 CTD may fold into a more stable conformation through interactions with the cell membrane.

Different functional domains in the cytoplasmic tail of glycoprotein B are involved in Epstein-Barr virus-induced membrane fusion

A virus-free cell fusion assay relying on the transient transfection of Epstein-Barr virus (EBV) glycoproteins into cells provides an efficient and quantitative assay for characterizing the viral requirements necessary for fusion of the viral envelope with the B cell membrane. Extensive cellular fusion occurred when Daudi cells were layered onto Chinese hamster ovary K1 cells transiently expressing EBV glycoproteins gp42, gH, gL, and gB. This is the first direct evidence that gB is involved in the process of EBV entry. Moreover, mutational analysis of gB indicates that the cytoplasmic tail contains two distinct domains that function differentially in the process of fusion. The region from amino acids 802 to 816 is necessary for productive membrane fusion, while amino acids 817 to 841 comprise a domain that negatively regulates membrane fusion.

Glycoprotein B of human herpesvirus 8 is a component of the virion in a cleaved form composed of amino- and carboxyl-terminal fragments

Human herpesvirus 8 (HHV-8) or Kaposi's sarcoma-associated herpesvirus (KSHV) is the only known human member of the Rhadinovirus genus of the gammaherpesvirus subfamily. Antibodies against peptides representing portions of the amino- and carboxyl-termini of HHV-8 gB were produced and used to detect gB expression in Vero cells transfected with the gB gene, in the HHV-8-harboring cell line, BCBL-1, and in purified virions. Expression of gB was detected in approximately 3% of uninduced BCBL-1 cells, while up to 30% of the cells expressed gB after 12-O-tetradecanoylphorbol-13-acetate (TPA) induction of virus replication. Indirect immunofluorescence assays and confocal microscopy showed that gB was distributed throughout the cytoplasm of BCBL-1 cells and transfected Vero cells. Immunoblot analyses of virion preparations revealed the presence of full-length as well as two smaller than full-length gB-derived species corresponding to the amino- and carboxy-terminal portions of gB, respectively. Biochemical analysis of the gB carbohydrate moieties using glycosylation inhibitors revealed that gB contained N-linked oligosaccharides of the high-mannose type, characteristic of precursor carbohydrate chains added in the endoplasmic reticulum.

Four consecutive arginine residues at positions 836-839 of EBV gp110 determine intracellular localization of gp110

Epstein-Barr virus (EBV) glycoprotein 110 (gp110) has sequence homology with herpes simplex virus-1 (HSV-1) gB; however the role of gp110 in EBVs' life cycle differs from that of gB. Unlike HSV-1 gB, which is essential for HSV-1 infection but dispensable for virus production, gp110 is required for assembly and egress of EBV. EBV gp110 is found mainly in the endoplasmic reticulum (ER)/nuclear membrane, whereas little or no gp110 is detected in the plasma membrane or a mature viral particle. Conversely, HSV-1 gB is abundant in the envelope of mature virions and in the plasma membrane as well as in the ER/nuclear membrane of HSV-1-infected cells. Interestingly, there are four consecutive arginine residues (at positions 836-839 of gp110) in the C-terminal domain previously shown to be important for gp110's intracellular localization. To determine whether these arginines function as an ER/nuclear localization signal, point mutants were constructed differentially substituting the four arginines. The glycosylation pattern and intracellular localization of the mutants were investigated by assessing sensitivity to endoglycosidase H (endo H) digestion and performing indirect immunofluorescence assays. Substitution of part of the four arginines changed the glycosylation profile and targeting of gp110. In addition, mutations preserving the net charge of the four arginines as well as those causing net charge shift resulted in the changed intracellular localization and altered glycosylation pattern. These results suggest that not only the net charge but also the conformation of the four arginines are important for gp110's processing and subcellular localization.

Human herpesvirus-8 glycoprotein B interacts with Epstein-Barr virus (EBV) glycoprotein 110 but fails to complement the infectivity of EBV mutants

To characterize human herpesvirus 8 (HHV-8) gB, the open reading frame was PCR amplified from the HHV-8-infected cell line BCBL-1 and cloned into an expression vector. To facilitate detection of expressed HHV-8 gB, the cytoplasmic tail of the glycoprotein was tagged with the influenza hemagglutinin (HA) epitope. Expression of tagged HHV-8 gB (gB-HA), as well as the untagged form, was readily detected in CHO-K1 cells and several lymphoblastoid cell lines (LCLs). HHV-8 gB-HA was sensitive to endoglycosidase H treatment, and immunofluorescence revealed that HHV-8 gB-HA was detectable in the perinuclear region of CHO-K1 cells. These observations suggest that HHV-8 gB is not processed in the Golgi and localizes to the endoplasmic reticulum or nuclear membrane. Because both HHV-8 and EBV are gamma-herpesviruses, the ability of HHV-8 gB to interact with and functionally complement EBV gp110 was examined. HHV-8 gB-HA and EBV gp110 co-immunoprecipitated, indicating formation of hetero-oligomers. However, HHV-8 gB-HA and HHV-8 gB failed to restore the infectivity of gp110-negative EBV mutants. These findings indicate that although HHV-8 gB and EBV gp110 have similar patterns of intracellular localization and can interact, there is not sufficient functional homology to allow efficient complementation.

Failure to complement infectivity of EBV and HSV-1 glycoprotein B (gB) deletion mutants with gBs from different human herpesvirus subfamilies

Glycoprotein B (gB) is conserved among the herpesvirus family which infects a broad range of species. To investigate the functional homology of human alpha-herpesviruses, beta-herpesviruses, and gamma-herpesviruses gB proteins, complementation studies were performed with gB genes from each subfamily member using EBV gp110 (EBV gB homologue) and HSV-1 gB null mutants. Neither the alpha-herpesvirus HSV-1 gB gene nor the beta-herpesvirus HCMV gB gene were able to complement the gp110 null mutant. Conversely, neither the beta-herpesvirus HCMV gB or the gamma-herpesvirus EBV gp110 gene were able to complement HSV-1 gB null mutants. To further investigate functional domains of EBV gp110 and HSV-1 gB, gB-gp110 chimeric proteins were constructed. Surprisingly, none of the chimeric proteins were able to complement either HSV-1 gB null mutants or EBV gp110 null mutants. These results demonstrate that there is not sufficient functional homology between the different gBs to allow complementation in other subfamily members of the herpesvirus family.

The Epstein-Barr virus glycoprotein 110 carboxy-terminal tail domain is essential for lytic virus replication

To investigate the importance of the Epstein-Barr virus (EBV) glycoprotein 110 (gp110) tail domain in the intracellular localization of gp110 and virus lytic replication, three carboxy-terminal truncation mutants of gp110 were constructed. Deletion of 16 amino acids from the carboxyl-terminal tail resulted in gp110 intracellular localization which was indistinguishable from that of wild-type gp110, whereas deletion of either 41 or 56 amino acids from the carboxyl-terminal tail of gp110 resulted in loss of retention of gp110 in the endoplasmic reticulum and nuclear membrane. None of the gp110 truncation mutants was able to complement EBV(gp110-)+ lymphoblastoid cell lines in transformation assays, indicating the importance of the gp110 tail domain in virus lytic replication. In electron microscopy analysis, no nucleocapsids or enveloped viruses were detected in EBV(gp110-)+ lymphoblastoid cell lines induced for lytic replication.

Glycoprotein 110, the Epstein-Barr virus homolog of herpes simplex virus glycoprotein B, is essential for Epstein-Barr virus replication in vivo

The Epstein-Barr virus (EBV) glycoprotein gp110 has substantial amino acid homology to gB of herpes simplex virus but localizes differently within infected cells and is essentially undetectable in virions. To investigate whether gp110, like gB, is essential for EBV infection, a selectable marker was inserted within the gp110 reading frame, BALF4, and the resulting null mutant EBV stain, B95-110HYG, was recovered in lymphoblastoid cell lines (LCLs). While LCLs infected with the parental virus B95-8 expressed the gp110 protein product following productive cycle induction, neither full-length gp110 nor the predicted gp110 truncation product was detectable in B95-110HYG LCLs. Infectious virus could not be recovered from B95-110HYG LCLs unless gp110 was provided in trans. Rescued B95-110HYG virus latently infected and growth transformed primary B lymphocytes. Thus, gp110 is required for the production of transforming virus but not for the maintenance of transformation of primary B lymphocytes by EBV.

Combined use of complement and anti-immunoglobulin in an enhanced neutralization assay for antibodies to varicella-zoster virus

An enhanced neutralization assay was developed to permit the sensitive, specific, and reproducible measurement of antibodies to varicella-zoster virus (VZV). Optimal neutralization was achieved using a combination of guinea pig complement (C') and rabbit anti-human IgG. This provided 625-, 160- and 13- to 64-fold increases in dilution endpoints of human post-zoster serum, varicella-zoster immune globulin and representative sera from recipients of live attenuated varicella vaccine, respectively, above those measured in the absence of C' and anti-IgG. The specificity of the assay was shown by the absorption of serum neutralization capacity with VZV-specific antigen and the lack of concordance between antibody titers to VZV with those to either herpes simplex virus type-2 or cytomegalovirus. The antibody status of recipients of live attenuated varicella vaccine was established from the amount of neutralizing activity produced at a single optimal serum dilution.

Detection of Epstein-Barr virus-specific antibodies by means of baculovirus-expressed EBV gp125

A major antigenic component of the Epstein-Barr virus viral capsid antigen (VCA) complex is the glycoprotein, gp125. Baculovirus-expressed gp125 reacted with Epstein-Barr virus IgG antibodies in a panel of 44 serum specimens using an immunoblot assay with over 97% sensitivity, and 100% specificity as compared to anti-VCA reactivity in an immunofluorescence assay. In addition, no evidence for cross-reactivity was seen in reactions with members of a panel of human serum specimens of known reactivity with each of the other known human herpesviruses. Thus, baculovirus-expressed gp125 should prove a stable platform on which new Epstein-Barr virus-specific serodiagnostic tests can be built.

Sensitive glycoprotein gIII blocking ELISA to distinguish between pseudorabies (Aujeszky's disease)-infected and vaccinated pigs

A blocking enzyme-linked immunosorbent assay (ELISA) test has been developed to distinguish pseudorabies virus (PRV) (Aujeszky's disease virus) -infected pigs from those immunized with a glycoprotein g92 (gIII) deletion mutant, PRV (dlg92dltk) [OMNIMARK-PRV]. This blocking ELISA test utilizes an anti-PRV gIII monoclonal antibody (mAbgIII)-horseradish peroxidase (HRPO) conjugate, TMB for color development and a cloned PRVg92 (gIII) antigen to coat wells of microtiter test plates. Undiluted sera are used to block the binding of the mAbgIII-HRPO conjugate to the antigen. The gIII blocking ELISA is specific and has a sensitivity comparable to screening ELISA and latex agglutination tests. PRV-negative sera and sera from pigs vaccinated once, twice, or four times with the gIII-negative vaccine all showed negative S/N values of greater than 0.70 (S/N defined as the optical density at 630 nm of test sera/optical density at 630 nm of negative control sera). Sera from PRV-infected herds, sera from pigs experimentally infected with virulent PRV, and sera from pigs vaccinated with modified-live or inactivated gIII+ vaccines were positive for gIII antibodies (S/N less than 0.7). Sera from pigs experimentally infected with 200 PFU virulent PRV seroconverted to gIII+ antibodies 7-10 days postinfection. Sera from pigs vaccinated with gpX- and gI- vaccines seroconverted to gIII+ antibodies 7-8 days after vaccination. The gIII antibodies persisted after gIII+ vaccinated for at least 376 days postvaccination. Sera from pigs protected by vaccination with PRV (dlg92dltk) and then challenge exposed to virulent PRV at 21 days postvaccination showed gIII+ antibodies by 14 days postchallenge. The specificity and sensitivity of the gIII blocking ELISA assay was further demonstrated on the United States Department of Agriculture-National Veterinary Services Laboratory (USDA-NVSL) sera from the 1988 PRV check set and the 1989 gIII PRV check set by comparing the gIII blocking ELISA assay with virus neutralization, screening/verification ELISA and latex agglutination assays.

Epstein-Barr virus types 1 and 2 differ in their EBNA-3A, EBNA-3B, and EBNA-3C genes

The two Epstein-Barr virus (EBV) types, EBV-1 and EBV-2, are known to differ in their EBNA-2 genes, which are 64 and 53% identical in their nucleotide and predicted amino acid sequences, respectively. Restriction endonuclease maps and serologic analyses detect few other differences between EBV-1 and EBV-2 except in the EBNA-3 gene family. We determined the DNA sequence of the AG876 EBV-2 EBNA-3 coding region and have compared it with known B95-8 EBV-1 EBNA-3 sequences to delineate the extent of divergence between EBV-1 and EBV-2 isolates in their EBNA-3 genes. The B95-8 and AG876 EBV isolates had nucleotide and amino acid identity levels of 90 and 84%, 88 and 80%, and 81 and 72% for the EBNA-3A, -3B, and -3C genes, respectively. In contrast, nucleotide sequence identity in the noncoding DNA adjacent to the B95-8 and AG876 EBNA-3 open reading frames was 96%. We used the polymerase chain reaction to demonstrate that five additional EBV-1 isolates and six additional EBV-2 isolates have the type-specific differences in their EBNA-3 genes predicted from the B95-8 or AG876 sequences. Thus, EBV-1 and EBV-2 are two distinct wild-type EBV strains that have significantly diverged at four genetic loci and have maintained type-characteristic differences at each locus. The delineation of these sequence differences between EBV-1 and EBV-2 is essential to ongoing molecular dissection of the biologic properties of EBV and of the human immune response to EBV infection. The application of these data to the delineation of epitopes recognized in the EBV-immune T-cell response is also discussed.

Glycoprotein gB of herpes simplex virus expresses type-common and type-specific antigenic determinants in vivo

Four monoclonal antibodies directed against glycoprotein B of herpes simplex virus were evaluated for their ability to immunize mice passively against acute virus-induced neurological illness and death when administered intraperitoneally 2 hours prior to footpad challenge with type 1 or type 2 virus. Two monoclonal antibodies, H120 and H157, failed to reduce the severity of neurological disease in infected animals. In contrast, H233 and H368 antibodies provided significant protection in type-common and type-specific fashions, respectively. A direct correlation was observed between in vitro neutralization and in vivo protection. These results provide the first in vivo evidence that glycoprotein gB of herpes simplex virus expresses both type-common and type-specific determinants during the evolution of acute virus-induced neurological disease.

Identification of a neutralizing epitope on glycoprotein gp58 of human cytomegalovirus

Human cytomegalovirus contains an envelope glycoprotein of 58 kilodaltons (gp58). The protein, which is derived from a glycosylated precursor molecule of 160 kilodaltons via proteolytic cleavage, is capable of inducing neutralizing antibodies. We have mapped the epitopes recognized by the neutralizing monoclonal antibody 7-17 and a second antibody (27-287) which is not neutralizing. Overlapping fragments of the carboxy-terminal part of the open reading frame coding for gp58 were expressed in Escherichia coli as beta-galactosidase fusion proteins. The reactivities of antibodies 7-17 and 27-287 were determined by Western blot (immunoblot) analysis. Both antibodies recognized sequences between amino acids 608 and 625 of the primary gp58 translation product. The antibodies almost completely inhibited one another in a competitive binding assay with intact virus as antigen. Moreover, antibody 27-287 was able to inhibit the complement-independent neutralizing activity of antibody 7-17.

ELISA tests and monoclonal antibodies for EBV

Monoclonal antibodies have now been prepared against a number of the major polypeptides associated with the different EBV-induced antigenic complexes. These antibodies have made it possible to purify and characterize most of these polypeptides and to identify the viral genes encoding for these proteins. In addition, new ELISA tests have been developed which measure antibodies in different immunoglobulin classes against the purified polypeptides. These assays have been useful in the diagnosis of EBV-associated diseases in clinical laboratories. The development of these antibodies and their application to the development of the new ELISA tests will be reviewed in this paper.

Abundant expression of herpes simplex virus glycoprotein gB using an adenovirus vector

Herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) is a major component of infected cell membranes and virion envelopes. Glycoprotein B is known to be essential for entry of viruses into cells and may play important roles in virus-induced cell fusion and other alterations in cell morphology. In order to study the biochemical and immunological properties of gB in isolation from other HSV-1 polypeptides we have constructed human adenovirus vectors capable of expressing high levels of gB. The gB gene was coupled to the SV40 early promoter and inserted into the E3 region of two adenovirus vectors, one in which the E1 region was deleted (AdgB-1) and another which contained E1 sequences (AdgB-2). In AdgB-1 the orientation of the chimeric gB-SV40 gene was right to left, i.e., opposite to the direction of late and E3 mRNA transcription, whereas in AdgB-2 the orientation was left to right. Human 293 cells which express E1 functions supported replication of AdgB-1 and gB was expressed in these cells but not in mouse cells and only at very low levels in human cells other than 293. Replication of AdgB-2 was not limited to 293 cells and the virus was able to induce synthesis of gB at levels equal to or higher than those expressed in HSV-1-infected human or mouse cells. Microscopic examination of AdgB-2-infected cells revealed extensive vacuolization in a manner completely uncharacteristic of adenovirus-infected cells, and fluorescent antibody staining indicated that gB was not only present at the cell surface but also concentrated in the cytoplasmic vacuoles.

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.