Analysis of early and late Epstein-Barr virus associated polypeptides by immunoprecipitation

Radioimmunoprecipitation in the diagnosis of chronic active Epstein-Barr virus infection

Chronic active Epstein-Barr virus (EBV) infection occurs sporadically in a small fraction of individuals infected with EBV. A clear definition of the disease and an unambiguous diagnostic test are still lacking. In an attempt to identify a serologic marker to facilitate the diagnosis, immunoblot and radioimmunoprecipitation assay (RIPA) were compared with standard immunofluorescence on 39 available sera. Results by RIPA revealed that antibodies to a 120 kDa viral protein correlated with the presence of chronic active EBV infection; these antibodies were not detected in sera from other EBV-seropositive individuals, with the exception of one of two patients with ataxia telangiectasia. Also, RIPA was the most sensitive technique for detecting EBV antibodies in sera weakly or doubtfully positive for antibody to EB viral capsid antigen by indirect immunofluorescence. All these sera had antibodies to the 150 kDa protein, also known as p160, the major viral capsid antigen.

Expression of the Epstein-Barr virus latent membrane protein (LMP) in insect cells and detection of antibodies in human sera against this protein

Recombinant baculoviruses containing the complete LMP and truncated LMP genes were generated and high levels of the LMP proteins were expressed in Spadoptera Frugiperda insect cells. A specific rabbit antiserum directed against the N-terminal part of LMP was obtained by immunizing the rabbits with Escherichia coli-expressed trpE-N-terminal part of LMP fusion protein. A total of 127 human sera were studied for their immune response to the recombinant full-length LMP. In immunofluorescence analysis, all sera tested showed no detectable reaction with the recombinant full-length LMP. In immunoprecipitation-immunoblotting analysis, however, sera from patients with nasopharyngeal carcinoma (5/22), patients with Hodgkin's disease (16/27), patients with other diseases exhibiting high EA-IgG titers (3/52), and VCA-IgG-positive healthy individuals (2/26) were shown to contain antibodies against this recombinant LMP. The expressed LMP proteins provided a sufficient and economic source of the proteins for further serological and biological studies.

Immunological characterization of the Epstein-Barr virus phosphoprotein PP58 and deoxyribonuclease expressed in the baculovirus expression system

The open reading frames of the phosphoprotein pp58 (BMRFI) and the deoxyribonuclease (BGLF5) of the Epstein-Barr-virus (EBV) strain M-ABA were cloned in the baculovirus expression vectors pAc373 and pAc360 and expressed in the Spodoptera frugiperda (SF158) insect cells. The recombinant phosphoprotein pp58 expressed in SF158 cells was recognized by the anti-pp58 rabbit anti-sera which were generated by immunizing rabbits with a TrpE-BMRFI fusion protein expressed in E. coli. DNA-cellulose chromatography showed that the recombinant pp58 exhibited DNA-binding activities. Immunofluorescence, immunoblot and ELISA analysis indicated that sera from patients with nasopharyngeal carcinoma (NPC) contained antibodies against pp58. The recombinant EBV DNase expressed in SF158 cells was recognized by the anti-EBV DNase rabbit anti-sera which were generated by immunizing rabbits with a TrpE-C-terminal part of BGLF5 fusion protein expressed in E. coli. The anti-EBV DNase rabbit anti-sera recognized also a protein of about 52 kDa in the EBV-harboring human B-cell lines Raji, Jijoye, B95-8, M-ABA and BL74 induced by TPA and n-butyrate. The recombinant EBV DNase exhibited exonuclease and endonuclease activities, a requirement for magnesium, and a high pH optimum (8.0). Its enzyme activities could be inhibited by sera from NPC patients and anti-EBV DNase rabbit anti-sera. Comparable studies of Raji EBV-DNase and recombinant EBV-DNase implied that recombinant EBV-DNase could also be used in the enzyme activity assay for the detection of NPC. In contrast to the enzyme inhibition test, immunofluorescence and immunoblot analysis demonstrated that the recombinant EBV DNase exhibited only a weak immunological reaction with NPC sera.

Immunoblotting reactivity of human sera from various sources against purified Epstein-Barr virus

The immunoblotting technique was used to analyse polypeptides of purified Epstein-Barr virus reacting with antibodies present in sera from clinically healthy individuals, from patients with infectious mononucleosis (IM) or AIDS, and from renal transplant recipients. Polypeptides with molecular sizes in the range of 40-290 kDa were detected. The 47- and 160-kDa nucleocapsid polypeptides, as well as the 72-, 74-, 140-, 220- and 290-kDa membrane polypeptides were the major viral proteins detected in the sera. Sera from clinically healthy individuals contained antibodies directed against all EBV membrane and nucleocapsid antigens. Sera from renal transplant recipients, from patients with IM and from patients with AIDS failed to react with certain nucleocapsid and membrane antigens; in particular, sera from AIDS patients and renal transplant recipients did not react with the 220-kDa polypeptide, one of the major membrane antigens, while sera from subjects with IM and from healthy individuals did. A high proportion of sera from patients with IM (38% vs 5% of clinically healthy individuals and 0-5% of the AIDS patients and renal transplant recipients) reacted with a 42-kDa polypeptide, suggesting its possible role in acute EBV infection.

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.

Both the rightward and the leftward open reading frames within the BamHI M DNA fragment of Epstein-Barr virus act as trans-activators of gene expression

The BamHI M DNA fragment of Epstein-Barr virus was shown to activate transcription of the cotransfected chloramphenicol acetyltransferase gene under the control of the simian virus 40 early promoter. Both the BamHI-BglII and the HindIII-BamHI subfragments of the BamHI M fragment, corresponding to the rightward reading frame BMRF1 and the leftward reading frame BMLF1, respectively, had the ability to activate transcription from the simian virus 40 promoter. The trans-activating function was well correlated with the expression of nuclear early antigens, which suggests that early antigens encoded by BMRF1 and BMLF1 are responsible for trans-activation and possibly play a role in regulated expression of virus genomes.

Enhancement of Epstein-Barr virus membrane protein (LMP) expression by serum, TPA, or n-butyrate in latently infected Raji cells

The BamHI Nhet region of the EBV DNA is known to code for two proteins. One is a membrane protein (LMP) with an apparent molecular weight of 60,000 on SDS-PAGE which is expressed in latently EBV infected cells. The second protein, so far unidentified, is presumably a late protein with a calculated molecular weight of 28,000 Da. Antisera against both proteins were generated by immunizing rabbits with either a fusion protein containing 155 amino acids of the C-terminus of LMP and a 37,000 mol wt piece of the bacterial anthranilate synthase or with a C-terminal synthetic peptide of 7 amino acids. These sera reacted with a protein varying in size between 60,000 and 65,000 mol wt on SDS-PAGE, found in all cell lines harboring EBV. In addition, these sera identified a second protein with an apparent molecular weight of 49,000 on SDS-PAGE in B95-8, P3HR-1, and M-ABA cells, which is presumably identical with the 28,000-Da protein mentioned above. Furthermore, with these sera a positive cytoplasmic immunofluorescence in 1 to 10% of the cells was obtained, depending on the cell line examined. Analyzing the nonproducer Raji cell line, the number of immunofluorescence-positive cells and the amount of the 60,000 protein, as judged by immunoblotting, was rapidly increased by addition of fresh medium with 10% fetal calf serum as well as by the tumor promoter TPA or to an even higher extend by n-butyrate. The kinetics of induction reached a maximum 24 hr after addition of medium plus 10% fresh serum or TPA or n-butyrate and decreased after 24 to 48 hr. Since the induction of the EBV early antigen (EA) associated proteins by TPA or n-butyrate exhibits a diverse kinetic with a maximum at 72 hr, the regulation of the 60,000 protein synthesis appears to be different from known EA-associated proteins.

Characterization of the Epstein-Barr virus-induced early polypeptide complex p50/58 EA-D using rabbit antisera, a monoclonal antibody, and human antibodies

A polypeptide complex (p52) belonging to the D-subspecificity of the EBV-induced early antigens (EA-D) was purified from chemically induced P3HR-1 cells. Rabbit antisera raised against the isolated polypeptides reacted with components of EA-D as could be shown by indirect immunofluorescence and immunoperoxidase staining of IdU-induced EA positive Raji cells, ELISA, and immunoblotting. In one-dimensional immunoblots the rabbit antisera detected a predominant polypeptide complex of 52 kDa. Two-dimensional immunoblots prepared with proteins from IdU-induced Raji cells showed that the rabbit sera detect three series of polypeptides of 52 kDa (pl 8.5-6.2), 55-58 kDa (pl 6.2-4.5), and 48-50 kDa (pl 6.0-4.5). These three groups of polypeptides could also be identified by 50 high titered anti-EA-D positive human sera and a specific monoclonal antibody (R3) as being the main components of EA-D in Raji and B95-8 cells. All polypeptides of the p50/58 complex showed DNA binding properties either by themselves or by an interaction with other proteins. When TPA or IdU-induced Raji cells were labeled with 2Pi, two phosphorylated polypeptides pp50 and pp58 could be immunoprecipitated with the rabbit sera and a high anti-EA titered human serum. The time course of the synthesis of polypeptides associated with the EA-D complex was studied by 2-D immunoblots: EA polypeptides of 52 kDa appeared as early as 6 hr after the addition of IdU to Raji cells in culture, polypeptides of 55-58 and 48-50 kDa after 18 and 25 hr, respectively. The coordinated appearance of these groups of polypeptides and their similar size and reactivity with human sera and rabbit antisera produced against the isolated p52 as well as with a monoclonal antibody (R3) suggested that most of these polypeptides are derived from post-translational modifications of one or a few initially synthesized polypeptides, possibly p52. Phosphorylation seems to be at least one possibility of post-translational modification.

The regulated expression of Epstein-Barr virus: evidence that the transition from primary to secondary protein synthesis in Raji cells superinfected with Epstein-Barr virus requires the synthesis of new RNA

In the presence of canavanine and the absence of arginine, superinfected Raji cells synthesize a limited spectrum of proteins (primary proteins). After the removal of canavanine at 8 h post infection, the cells proceed after a lag phase of 2-3 h to synthesize a second group of proteins. The appearance of these proteins can be prevented by addition of actinomycin-D to the chase media, suggesting that active primary proteins are required for the synthesis of new mRNA coding for the secondary proteins.

Novel nuclear antigens recognized by human sera in lymphocytes latently infected by Epstein-Barr virus

We have used three latently infected cell lines, X50-7, JC-5, and Raji, to identify two new nuclear antigen complexes by Western immunoblotting with human anti-EBNA (Epstein-Barr Virus Nuclear Antigen) sera. One antigen complex, termed EBNA III, is composed of a group of high molecular weight proteins between 130 and 160 kDa and the other antigen complex, termed EBNA IV, is a size-related group of polypeptides between 28 and 62 kDa. Both the EBNA III and EBNA IV groups of proteins display variation in size among the different strains of EBV. Cell fractionation of X50-7, JC-5, Raji, and C16, a cell clone of P3HR1, showed that both new antigen complexes were completely recovered from the nuclei of latently infected lymphocytes as were previously described EBNA I and II. Because these new antigens are only detected by anti-EBNA sera in EBV infected cells, it seems likely that they may be encoded by the viral genome and play some role in the immortalization of lymphocytes by the virus.

Purification of a polypeptide complex (p52) belonging to the D-subspecificites of Epstein-Barr virus-induced early antigens

A two-dimensional immunoblot analysis of chemically induced EBV DNA carrying Burkitt's lymphoma cell lines shows besides a large number of minor components at least two major groups of polypeptides: the most prominent group of polypeptides is observed in the range of 48 to 58 kDa (pI 4.5 to 8.5) and another group at 38/36 kDa (pI 4.4). A polypeptide complex (p52) belonging to the Epstein-Barr virus (EBV)-induced early antigen complex (EA) has been isolated from IdU-induced Raji and B95-8 cells as well as from n-butyrate-induced P3HR-1 cells. The p52 polypeptides have been purified by chromatography on Blue-, DEAE-, CM-, and Phenyl-Sepharose. The purification of these components of the EA complex was monitored by ELISA and by two-dimensional immunoblots using a well-characterized high anti-EBV positive human serum. The isolated polypeptides have an apparent mol wt of about 52,000 Da as determined under nondenaturing conditions by gel filtration chromatography on Sephacryl S-300. One- and two-dimensional immunoblots show a major group of polypeptides of 52 kDa (pI 8.5 to 5.5) with EA activity and some minor components with smaller size up to 40 kDa. The latter seem to be generated by limited proteolysis of p52 polypeptides. The EA activity of the isolated polypeptides could be confirmed by their reaction with IgG anti-EA positive as well as IgA anti-EA positive sera by ELISA. The purified polypeptide complex did not react with anti-EA-D negative, anti-EA-R positive sera obtained from patients with African Burkitt's lymphoma, suggesting that these polypeptides belong to the EA-D complex. The monoclonal antibody R3 reacted with the isolated 52 kDa components of EA suggesting a common epitope present on these polypeptides, the same result was obtained with three rabbit sera produced against the isolated polypeptide complex.

Biochemical characterization of two Epstein-Barr virus early antigen-associated phosphopolypeptides

Epstein-Barr virus (EBV) nonproducer cells NC37 induced to viral early antigen (EA) synthesis by the tumor promotor 12-O-tetradecanoylphorbol-13-acetate (TPA) were labeled at Day 4 after induction with 32P, and were analyzed by immunoprecipitation with human EA-positive sera. By employing this method the appearance of two phosphopolypeptides of 50 and 58K (pp50 and pp58) was well correlated with EA complex. Partial V8 protease digestion and two-dimensional peptide analysis revealed that the polypeptides pp50 and pp58 are related. The analysis of phosphoamino acids indicated that pp58 contains phosphoserine and phosphothreonine to the same percentage, whereas in pp50 only phosphoserine was found. The analysis of the subcellular distribution revealed that pp50 and pp58 are located in the chromatin. Both phosphopolypeptides exhibit DNA-binding activity, and are recognized by two monoclonal antibodies described recently (R3 and 1108-1).

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.

Qualitative and quantitative analyses of Epstein-Barr virus early antigen diffuse component by western blotting enzyme-linked immunosorbent assay with a monoclonal antibody

We report the use of monoclonal antibody against the early antigen diffuse component (anti-EA-D) of Epstein-Barr virus (EBV) to analyze, both qualitatively and quantitatively, the expression of EA-D in various human lymphoblastoid cell lines activated by chemical inducers. The kinetics of synthesis of EA-D in P3HR-1, B95-8, and Ramos/AW cells were similar in that they all reached the peak of synthesis on day 5 after induction. Surprisingly, no expression of EA-D was found in induced BJAB/GC, an EBV-genome-containing cell line. EBV-negative cell lines, BJAB and Ramos, were negative for EA-D. Raji cells had no detectable EA-D but responded rapidly to induction, reaching a peak on day 3. Superinfection of Raji cells also resulted in marked induction of EA-D, which reached a plateau between 8 to 12 h postinfection. Western blotting coupled with the enzyme-linked immunosorbent assay was employed to identify polypeptides representing EA-D. A family of four polypeptides with molecular weights of 46,000 (46K protein), 49,000, 52,000, and 55,000 were identified to be reactive with monoclonal anti-EA-D antiserum. The pattern of EA-D polypeptides expressed in each cell line was different. Of particular interest was the expression of a large quantity of 46K protein both in induced Raji and P3HR-1 cells, but not in superinfected Raji cells. A 49K doublet was expressed in activated p3HR-1, B95-8, and Ramos/AW cells and in superinfected Raji cells. In addition, two distinct 52K and 55K polypeptides were expressed in induced Ramos/AW and superinfected Raji cells. However, none of these EA-D polypeptides was detectable in BJAB/GC, BJAB, Ramos, and mock-infected Raji cells. To approximate relative concentrations of EA-D in cell extracts, we employed the enzyme-linked immunosorbent assay and immunoblot dot methods by using one of the purified EA-D components to construct a standard curve. Depending upon the cell lines, it was estimated that ca. 1 to 3% (determined by the enzyme-linked immunosorbent assay) and 0.8 to 1.6% (determined by immunoblot dot) of total proteins from maximally induced cells were EA-D. These results suggest that differential expression of EA-D polypeptides could be of importance in the diagnosis of state of EBV infection.

Mapping of Epstein-Barr virus proteins on the genome by translation of hybrid-selected RNA from induced P3HR1 cells and induced Raji cells

RNA was isolated from induced P3HR1 cells which synthesize Epstein-Barr virus (EBV) particles and therefore a full set of early and late antigens and from induced Raji cells which synthesize only early EBV proteins and hybridized to cloned EBV-DNA fragments spanning the entire genome. Bound mRNA was eluted and translated in vitro with rabbit reticulocyte lysate. The translation products were analyzed on SDS-polyacrylamide gels either directly or after immunoprecipitation with human sera. Most proteins could be mapped to short defined regions of the EBV genome using short restriction fragments and overlapping sheared fragments and there is evidence of splicing for some mRNA species. The synthesis of five early proteins can be seen only with hybrid-selected RNA from induced Raji cells. These mRNAs seem to be enriched in the cells restricted to early antigen synthesis.

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 mapping of polypeptides encoded by the P3HR-1 strain of Epstein-Barr virus

The Epstein-Barr virus (EBV)-specified polypeptides induced upon viral replication in the P3HR-1 cell line have been examined by immunoprecipitation with a high-titer human anti-EBV serum. Twenty-five predominant polypeptides were identified in cell extracts, whereas 18 polypeptides were precipitated from cell-free translation reactions directed by total mRNA. Hybrid selection of mRNA to the BamHI DNA clones of the EBV genome and immunoprecipitation of the corresponding cell-free translation products revealed 98 EBV-specified polypeptides and their coding location along the viral genome. In addition, the viral polypeptides that bind reversibly to DNA-cellulose have been characterized and the deduced map locations of this functional group of EBV-specified polypeptides is presented.

Expression of a nuclear and a cytoplasmic Epstein-Barr virus early antigen after DNA transfer: cooperation of two distant parts of the genome for expression of the cytoplasmic antigen

Expression of Epstein-Barr virus (EBV) antigens was studied after transfection of cloned EBV DNA fragments into baby hamster kidney (BHK) cells. A set of seven widely overlapping clones covering the whole genome of the non-defective Epstein-Barr virus strain M-ABA was used for transfection. Transfer of the cosmid clones into BHK cells resulted in expression of two distinct antigens, as revealed by indirect immunofluorescence using human anti-EBV sera. Staining with human sera of different reactivity against EBV-associated antigens revealed that both types of antigens were related to the early antigen complex. The first type of antigen was detected only in the nuclei of BHK cells that had received DNA of a clone containing HindIII-G, -H, -E, -I2, -O, -I1, and -P. The second type of antigen was found in the cytoplasm of cells cotransfected with clones containing Sal-A and HindIII-I2, -O, -I1, -P, and -C, whereas transfection of both individual clones failed to induce the antigen. Further analysis with subclones identified HindIII-G (5 kilobases) and HindIII-I2 (3 kilobases) plus the rightmost 3 kilobases of Sal-A as the sequences responsible for expression of the nuclear and the cytoplasmic antigen, respectively. The fact that two distant regions of the viral genome are required for expression of a viral antigen provides evidence for intergenomic regulation that can be studied in vitro.

Immunobiochemical characterization with monoclonal antibodies of Epstein-Barr virus-associated early antigens in chemically induced cells

Five monoclonal antibodies which are reactive to early antigens of Epstein-Barr virus have been produced by using somatic cell hybridization techniques. The specificity of the monoclonal antibodies to early antigens was demonstrated by indirect immunofluorescence, which showed that the antigens were localized to the nucleus of early antigen-induced Raji cells. Additional indirect immunofluorescence studies showed that like patient antisera to diffuse-staining early antigen, the monoclonal antibodies gave positive staining reactions after methanol fixation. One of the antibodies, 1150-4, was positive by the anti-complement immunofluorescence technique but differed with Epstein-Barr virus-associated nuclear antigen-positive patient sera in that it only stained induced cells. Different fixation methods were found to alter dramatically the appearance of the nuclear staining reactions produced by the monoclonal antibodies. Immunoprecipitation and immunoblot experiments revealed that monoclonal antibodies 1108-1 and 1129-1 recognized two polypeptides of 55,000 and 50,000 daltons (p55;50), 1173-6 and 1180-2 recognized just p50, and 1150-4 identified a 65,000-dalton nuclear protein. Immunobiochemical characterization of these viral antigens showed that p55 is a phosphoprotein, and p55;50 has strong DNA-binding activity preferentially to single-stranded DNA. Elucidation of the role of these nuclear proteins in Epstein-Barr virus infection and the events associated with Epstein-Barr virus-directed lymphocyte transformation may provide significant information on the pathogenicity of this important human virus.

Enzyme-linked immunosorbent assay for IgG antibodies to Epstein-Barr virus-associated early antigens and viral capsid antigen

An enzyme-linked immunosorbent assay has been developed for the detection of IgG antibodies to Epstein-Barr virus-associated early antigens and late antigens including the viral capsid antigen. The antibody titers of human sera determined in this way correlate well with those by indirect immunofluorescence. ELISA was more sensitive than the IF method. The assays described may be used for rapid and sensitive diagnosis of EBV-related diseases. In addition, the ELISA will be useful for the determination of antibody titers to isolated EBV-associated antigens, e.g., purified components of the EA complex.

Production of monoclonal antibody to a late intracellular Epstein-Barr virus-induced antigen

A monoclonal antibody designated L2 was produced against a late intracellular protein induced by Epstein-Barr virus (EBV). This protein was expressed in cells producing virus but not in EBV genome-positive nonproducer cell lines, EBV genome-negative cell lines, or producer cultures cultivated in the presence of phosphonoacetic acid as determined by immunofluorescence. In addition, the antibody did not react with the membranes of infected cells indicating that it was not directed against an EBV-induced membrane antigen component. The monoclonal antibody was shown to recognize a glycoprotein with a molecular weight of approximately 125K by SDS-polyacrylamide gel electrophoresis. This glycoprotein was consistently found to be slightly larger when isolated from the P3HR-1 cell line as opposed to the B-95-8 cell line. A similar difference was also noted by comparison of peptide maps of this protein isolated by immunoaffinity chromatography from the two cell lines. Serological studies indicated that this 125K glycoprotein was a major component of the viral capsid-antigen (VCA) complex as defined by immunofluorescence.

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.

Pattern of Epstein-Barr virus (EBV)-specific proteins synthesized during primary lytic infection of mouse lymphocytes by EBV

Normal mouse lymphocytes were implanted with EBV receptors and exposed to the virus of P3HR-1 strain. 5% of the cells expressed early (EA) and viral capsid (VCA) antigens as assayed by immunofluorescence 24 h after the infection. Only 0.1% of cells expressed nuclear-like antigen (EBNA) 48 h post-infection. When labelled metabolically with [35S]methionine, extracted, immunoprecipitated with EBV-positive sera, and analyzed by SDS-gel electrophoresis and autoradiography, about 20 EBV-determined proteins ranging from 19 to 165 kd were detected. Their pattern and relative quantitative expression differed from those in P3HR-1 virus superinfected Raji cells. Polypeptides of approximate molecular size 78, 72, 65, 48 and 26.5 kd were predominant in EBV-infected mouse lymphocytes. In contrast, 130, 98, 59, 50.5 and 36 kd proteins were predominant in the induced Raji cells. Our results demonstrate that rodent lymphocytes can be used for the direct biochemical analysis of EBV-translational products during primary lytic infection in normal cells.

Purification of a protein (60K/58K) associated with the Epstein-Barr virus-induced early antigen complex in Raji cells

A double antibody sandwich ELISA has been established for the detection and quantitation of EBV-associated early antigens (EA) in IUdR-induced Raji cells. The EA complex extracted from Raji cells could be separated by ion exchange chromatography and isoelectric focusing into several components. One EA-associated subspecificity has been purified by DEAE-, CM-, and Blue-Sepharose chromatography followed by isoelectric focusing. The isolated protein has an apparent molecular weight of 240,000 +/- 20,000 daltons under non-dissociating conditions on Sephacryl S-300, an isoelectric point of 4.5, and seems to be composed of two polypeptides of 60,000 and 58,000 daltons as shown by SDS-gel electrophoresis and two-dimensional gel electrophoresis. Preliminary data indicate that the 58,000 polypeptide is generated by limited proteolysis of the 60,000 polypeptide. The EA activity of the isolated protein has been confirmed by the double antibody sandwich ELISA and its reactivity with anti-EA-positive sera in an ELISA for the detection of anti-EA antibodies.

Multiplicity-dependent induction of viral capsid antigen in Raji cells superinfected with Epstein-Barr virus

A quantitative analysis of Epstein-Barr virus (EBV)-induced early antigen (EA) and viral capsid antigen (VCA) syntheses was carried out in Raji cells superinfected with purified, concentrated P3HR-1 EBV. When the cells were exposed to the virus and assessed by immunofluorescence and immunoprecipitation, EA induction occurred significantly (17%) but not VCA (less than 1%), at a low-input multiplicity of infection (MOI) of 10 EBV DNA copies/cell. In contrast, at a high MOI of 500 EBV DNA copies/cell, the majority of cells were positive for both EA (82%) and VCA (61%). The latter VCA synthesis was accompanied by the replication of EBV DNA. Kinetic studies showed that EA induction was directly proportional to the dilution of the infecting virus, while VCA was made following three-hit kinetics. The implications of these results are discussed in relation to the heterogeneous nature of P3HR-1 EBV and a possible role of EA in VCA synthesis.

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.

Biochemical studies on structural and nonstructural proteins of the African green monkey B-lymphotropic papovavirus (LPV)

African green monkey (AGM) B-lymphotropic papovavirus (LPV) particles were separated from infected B-lymphoma BJA-B cells by neuraminidase and deoxycholate treatment and were further purified twice by CsCl density centrifugation. The SDS-PAGE analysis of virus particles banding at a density of 1.3510 g/ml and radioactively labeled by 125I revealed a major polypeptide of 40,000 and two minor polypeptides of 42,000 and 29,000. In addition, in infected BJA-B cells, all three viral structural polypeptides could be identified by immunoprecipitation. A nonstructural phosphopolypeptide of approximately 90,000 MW could be detected when sera against SDS-denatured SV40 T antigen or an AGM serum pool were used for immunoprecipitation. It is suggested that the 90K polypeptide of LPV represents an equivalent to T antigens of other papovaviruses.

Synthesis and processing of the three major envelope glycoproteins of Epstein-Barr virus

In pulse-chase experiments, the three major Epstein-Barr virus envelope glycoproteins, gp350/300, gp250/200, and gp85, were shown to be synthesized from separate precursors of 190,000, 160,000, and 83,000 daltons, respectively. These three pulse-labeled species were chased into the mature forms of the glycoproteins between 1 and 3 h after transfer to nonradioactive medium. Digestion of precursor forms with endo-beta-N-acetylglucosaminidase H (endo H) yielded polypeptides of 160,000, 120,000, and 75,000 daltons. Comparison of these results with those from experiments with tunicamycin, which specifically blocks N-linked glycosylation, indicated that some other post-translational modification(s), probably O-linked glycosylation, contributes about 100,000 and 60,000 daltons of apparent molecular mass to gp350/300 and gp250/200, respectively. Experiments with endo H showed that mature gp350/300 and gp250/200 contain complex-type (endo H-resistant) N-linked glycosyl chains, whereas gp85 contains both high-mannose (endo H-sensitive)- and complex-type oligosaccharides. In contrast to the results obtained with the three envelope glycoproteins, no precursor forms of the two unglycosylated protein, p160 (the major Epstein-Barr virus capsid antigen) and p140 (an envelope protein), were detected. The partial proteolytic maps of gp350/300 and gp250/200 were quite similar, suggesting that polypeptide sequence homology could account for at least part of the observed serological cross-reactivity of the two proteins. Taken together, these results demonstrate that the polypeptide portions of gp350/300 and gp250/200 are closely related but not derived from a common precursor. Furthermore, the polypeptide portions comprise half or less of the apparent molecular weight of the mature glycoproteins on sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Activation of latent Epstein-Barr virus genomes: selective stimulation of synthesis of chromosomal proteins by a tumor promoter

The tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) is a potent inducer of Epstein-Barr virus (EBV) gene expression. The optimal conditions for maximum activation of latent EBV genomes by TPA were determined. Although TPA is able to induce replication of EBV genomes in P3HR-1 cells in all phases of growth, the greatest increase in viral genome copies per cell (15-fold above the control level) occurred in nonproliferating cells as opposed to cells growing exponentially (6-fold above the control level). The synthesis of chromosomal proteins in nonproliferating cells under the conditions that induce maximum activation of latent virus genomes by TPA was studied. Selective stimulation in chromosomal protein synthesis accompanied the increase in EBV genomes in P3HR-1 cells despite an overall reduction in total cellular protein synthesis. Comparison of the chromosomal proteins from TPA-induced P3HR-1 cells and from superinfected Raji cells revealed comigrating chromosomal polypeptides of 145K, 140K, 135K, 110K, 85K, and 55K that are presumably EBV associated. The selective stimulation of synthesis of these chromosomal proteins in TPA-treated P3HR-1 cells was closely associated with the activation of latent EBV genomes.

Antigens in an adult T-cell leukemia virus-producer cell line: reactivity with human serum antibodies

Sera from patients with adult T-cell leukemia (ATL) or other diseases and from healthy adults, whose titers of antibodies against ATL-associated antigens (ATLA) had been determined by indirect immunofluorescence, were analysed by a procedure of immunoprecipitation followed by SDS-polyacrylamide gel electrophoresis. For this an ATL virus (ATLV)-producer cell line, MT-2, was labelled with [35S]-methionine. All 12 anti-ATLA-positive sera but none of the eight anti-ATLA-negative sera tested reacted specifically with four polypeptides with molecular weights of 70,000, 53,000, 36,000 and 24,000 daltons. Furthermore, enrichment of three polypeptides with molecular weights of 76,000, 43,000 and 28,000 daltons was observed on reaction with anti-ATLA-positive sera. In control experiments using ATLA-negative T-cell lines, Molt-4 and HPB-ALL, none of these seven polypeptides were precipitated by reaction with anti-ATLA-positive sera. All six anti-ATLA-positive sera tested were shown to react with a polypeptide with a molecular weight of 24,000 of purified ATLV.

Mapping of polypeptides encoded by the Epstein-Barr virus genome in productive infection

Over 30 viral-specified polypeptides are translated in vitro from RNA of cells productively infected with Epstein-Barr virus (EBV). The polypeptides map to sites in EBV DNA by hybrid selection. Almost all of the polypeptides are reactive with EBV immune human serum. Several of the polypeptides are part of the early antigen complex. Two others are likely to be major structural components of the virus. Genes encoding persistent early and late polypeptides are intermixed through most of the EBV genome.

Epstein-Barr virus RNA. VIII. Viral RNA in permissively infected B95-8 cells

More than 50 RNAs expressed by Epstein-Barr virus late in productive infection have been identified. B95-8-infected cells were induced to a relatively high level of permissive infection with the tumor promotor 12-O-tetradecanoylphorbol-13-acetate. Polyadenylated RNAs were extracted from the cell cytoplasm, separated by size on formaldehyde gels, transferred to nitrocellulose, and hybridized to labeled recombinant Epstein-Barr virus DNA fragments. Comparison of RNAs from induced cultures with RNAs from induced cultures also treated with phosphonoacetic acid to inhibit viral DNA synthesis identifies two RNA classes: a persistent early class of RNAs whose abundance is relatively resistant to viral DNA synthesis inhibition and a late class of RNAs whose abundance is relatively sensitive to viral DNA synthesis inhibition. The persistent early and late RNAs are not clustered but are intermixed and scattered through most of segments UL and US. The cytoplasmic polyadenylated RNAs expressed during latent infection were not detected in productively infected cells, indicating that different classes of viral RNA are associated with latent and productive infection. Non-polyadenylated small RNAs originally identified in cells latently infected with Epstein-Barr virus are expressed in greater abundance in productively infected cells and are part of the early RNA class.

Epstein-Barr virus induced proteins V: comparison of EBV-specific polypeptides from different virus strains

EBV-associated polypeptides induced in different Epstein-Barr Virus (EBV)-producing cell lines by the tumor promotor TPA, and from purified EBV particles derived from the same lines were radioactivity labeled and analyzed by immunoprecipitation with human VCA+MA+ sera. In virus-producing cells no significant differences in the molecular weight of 35S-methionine-labeled EBV-associated polypeptide patterns could be observed. The analysis 125I-labeled polypeptides from purified virus particles of four different strains revealed that, in addition to common polypeptides, individual EBV strains contain strain-specific high molecular weight glycopolypeptides. These polypeptides, constituting part of the membrane antigen complex, are present in varying amounts. While P3HR-1 virus particles contain a major component of 250 000 and small amounts of 340 000 molecular weight polypeptides, Q IMR-WIL virus particles have more 340 00 than 240 000 molecular weight polypeptides. Furthermore, in B95-8 particles and in particles from an EBV strain isolated from an African green monkey (AGM-EBV) respectively, large amounts of 360 000 and 250 000 polypeptides could be observed. Since these glycopolypeptides carry strain-, subgroup- and group-specific antigenic determinants, also found in virus strains produced in human and marmoset cells, it should be further investigated whether these differences in molecular weight are virus-strain- or cell-specific.

Filamentous structures associated with Epstein-Barr virus-infected cells

After the onset of Epstein-Barr virus DNA and protein synthesis 10 h after superinfection of Raji cells (a cell line containing Epstein-Barr virus DNA but not producing virus), filamentous structures 25 nm in diameter and 0.2 to 1.4 micrometers in length could be detected in the cell cytoplasm by electron microscopy. These structures banded in metrizamide gradients with viral DNA and proteins, but at a density different from that of virions or nucleocapsids. These filaments, enriched in a 155,000-dalton protein similar in size to a major nucleocapsid protein of Epstein-Barr virus, may represent intermediates in viral nucleocapsid assembly.

Production and characterization of monoclonal antibodies against the Epstein-Barr virus membrane antigen

Five murine hybridoma lines that produce monoclonal antibodies against Epstein-Barr virus membrane antigen (MA) were established. Immunoprecipitation experiments demonstrated that three of the antibodies precipitated both the 236,000 (236K) MA and the 212K MA. The other two antibodies precipitated the 86K MA. Antibodies against the 236K-212K MA and the 86K MA mediated complement-dependent cytolysis of Epstein-Barr-virus-infected cells. The antibodies against the 86K MA neutralized both the B95-8 and P3HR-1 viruses.

Two large virion envelope glycoproteins mediate Epstein-Barr virus binding to receptor-positive cells

The four major Epstein-Barr virion envelope components were separated by column chromatography and reconstituted into artificial liposomes. These liposomes were tested for their ability to bind selectively to Epstein-Barr virus receptor-positive cells. Only when the two high-molecular-weight glycoproteins, VE1 and VE2, were present together was a stable binding complex formed. The addition of the other virion envelope components did not increase the levels of binding. This binding was inhibited by unlabeled viable virions and by neutralizing antisera, which recognized the two components. Adsorption of viable virus was also eliminated by the antisera. The enzyme susceptibility pattern of the cell-liposome interaction is similar to that of the virus-cell interaction, thus confirming the specificity of the binding site. A model for Epstein-Barr virus binding in which VE1 and VE2 coordinately recognize the same binding site is presented.

Epstein-Barr virus strain- and group-specific antigenic determinants detected by monoclonal antibodies

In order to differentiate Epstein-Barr virus (EBV) strains by serological markers we prepared hybridomas producing monoclonal antibodies against polypeptides of the QIMR-WIL EBV strain. These monoclonal antibodies were screened by indirect immunofluorescence techniques. Immunoprecipitation using EBV-positive monoclonal antibodies and the protein A method, of 125I-labelled polypeptides from purified QIMR-WIL EBV particles, revealed that a series of monoclonal antibodies against the four main surface and envelope polypeptides precipitating p340, p340/p240, p140, and p80 were obtained. When 125I-labelled polypeptides from purified P3HR-1 and B95-8 EBV particles were immunoprecipitated, it could be demonstrated that several anti-p340 (QIMR-WIL) antibodies recognized strain-specific antigenic determinants, while anti-p340/p240 (QIMR-WIL) as well as anti-p140 (QIMR-WIL) antibody clones reacted with antigenic sites which are in common wither among B95-8 or in addition to P3HR-1 polypeptides. Thus, monoclonal antibodies now provide a serological basis for EBV typing.

Epstein-Barr virus polypeptides: identification of early proteins and their synthesis and glycosylation

We have identified at least six early polypeptides induced by Epstein-Barr virus in cells or under conditions which are nonpermissive for Epstein-Barr virus DNA replication ranging in molecular weight from 140,000 to 26,000.

Identification of an Epstein-Barr virus nuclear antigen by fluoroimmunoelectrophoresis and radioimmunoelectrophoresis

A 65,000-dalton (65K) antigen found in Raji cells by fluoroimmunoelectrophoresis and radioimmunoelectrophoresis has been identified as an Epstein-Barr virus nuclear antigen (EBNA). This identification is based on the following evidence. The 65K antigen is detected in Raji cells but not in three Epstein-Barr virus (-) human B cell lines. It is not detected with EBNA (-) sera. The 65K antigen is found predominantly in the nucleus and co-elutes with EBNA during partial purification by DNA-Sepharose and Blue Dextran-Sepharose chromatography. Finally, the partially purified 65K antigen is an effective absorbant of EBNA antibody as measured in an anticomplement immunofluorescence assay. Antigens with molecular weights of 72, 70, and 73K have been detected in B95-8, P3HR-1, and Namalwa cells, respectively. These antigens are the likely homologues of the 65K Raji EBNA. In addition, an Epstein-Barr virus-associated, 81K DNA-binding antigen has been detected in both B95-8 and Raji cells.

Epstein-Barr virus polypeptides: effect of inhibition of viral DNA replication on their synthesis

After Epstein-Barr virus superinfection of the human lymphoblastoid cell line Raji, a Burkitt lymphoma-derived line that contains Epstein-Barr virus genomes in an episomal form, at least 40 polypeptides could be resolved by polyacrylamide gel electrophoresis. Eleven of the 40 polypeptides were immunoprecipitable by early antigen+/viral capsid antigen+ antiserum. The polypeptides could be divided into six classes, immediate-early, early, intermediate, late, very late, and persistent, depending upon the time of synthesis. Ten of the 40 polypeptides appeared to preexist before superinfection and persisted despite general cessation of host protein synthesis; none of the persistent proteins was immunoprecipitated by the Epstein-Barr virus antibody-containing serum. When viral DNA replication was blocked by a variety of inhibitors of DNA synthesis, a number of different patterns of polypeptide synthesis could be detected. The synthesis of six polypeptides was blocked by the most virus-specific inhibitors, acyclovir and phosphonoacetic acid. Additionally, in the presence of 1-beta-D-arabinofuranosylcytosine, 1-beta-D-arabinofuranosyladenine, and methotrexate, seven polypeptides showed oversynthesis.

Monoclonal antibody against a 250,000-dalton glycoprotein of Epstein-Barr virus identifies a membrane antigen and a neutralizing antigen

An antibody-secreting hybrid cell line was produced by fusion of mouse myeloma cells with splenocytes from mice immunized with virions of the B95-8 strain of Epstein-Barr Virus (EBV). The monoclonal IgG antibody was shown to have anti-EBV activity by the following criteria: (i) It reacted with the membranes and the cytoplasm of seven different EBV-producing lines, but with no nonproducing line. (ii) The individual cells identified by the murine antibody were shown to be the same cells identified by a human serum having anti-EBV activity. (iii) The antibody significantly reduced the infectivity of two independent strains of EBV (namely, P3HR1K and B95-8). The antigen being recognized was characterized by immunoprecipitations of radiolabeled EBV-producer cell lysates. A single glycoprotein with an estimated molecular weight of 250,000 was identified. It is concluded that neutralization of EBV can be achieved by an IgG-class monoclonal antibody directed against a single antigenic site on a 250,000-dalton glycoprotein, which is a constituent of the EBV virion.