Low frequency of apoptosis in Epstein-Barr virus-associated gastric carcinoma with lymphoid stroma

In order to understand the character of Epstein-Barr virus (EBV)-associated gastric carcinoma with lymphoid stroma (GCLS), we examined cell proliferation and death in comparison with gastric carcinoma without prominent lymphoid stroma (conventional gastric carcinoma). The EBV-encoded small RNA I (EBER-1) and apoptotic cells were examined by in situ hybridization (ISH) and by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end-labeling (TUNEL), respectively, on formalin-fixed paraffin-embedded surgical specimens from 22 GCLSs and 23 conventional gastric carcinomas. Immunostaining was performed for the detection of Ki-67 antigen (Ki-67), P53 protein (P53) and bcl-2 oncoprotein (BCL-2). The percentages of apoptotic and Ki-67-positive cells were expressed as apoptotic indices (AI) and Ki-67 labeling indices (KI), respectively. EBER-1 was detected in 19 (86%) GCLSs in contrast to none in conventional carcinomas. Mean AI was 1.8 +/- 0.6 in the EBER-1-positive GCLSs and 3.3 +/- 1.7 in the conventional gastric carcinomas, the value being significantly lower in the former (p < 0.01). Mean KI was 40.0 +/- 10.8 in the GCLSs and 48.5 +/- 9.1 in the conventional gastric carcinomas, the value being significantly lower in the former (p < 0.05). P53 expression showed no significant difference between the 2 categories of carcinoma.

Low frequency of apoptosis in Epstein-Barr virus-associated gastric carcinoma with lymphoid stroma

In order to understand the character of Epstein-Barr virus (EBV)-associated gastric carcinoma with lymphoid stroma (GCLS), we examined cell proliferation and death in comparison with gastric carcinoma without prominent lymphoid stroma (conventional gastric carcinoma). The EBV-encoded small RNA I (EBER-1) and apoptotic cells were examined by in situ hybridization (ISH) and by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end-labeling (TUNEL), respectively, on formalin-fixed paraffin-embedded surgical specimens from 22 GCLSs and 23 conventional gastric carcinomas. Immunostaining was performed for the detection of Ki-67 antigen (Ki-67), P53 protein (P53) and bcl-2 oncoprotein (BCL-2). The percentages of apoptotic and Ki-67-positive cells were expressed as apoptotic indices (AI) and Ki-67 labeling indices (KI), respectively. EBER-1 was detected in 19 (86%) GCLSs in contrast to none in conventional carcinomas. Mean AI was 1.8 +/- 0.6 in the EBER-1-positive GCLSs and 3.3 +/- 1.7 in the conventional gastric carcinomas, the value being significantly lower in the former (p < 0.01). Mean KI was 40.0 +/- 10.8 in the GCLSs and 48.5 +/- 9.1 in the conventional gastric carcinomas, the value being significantly lower in the former (p < 0.05). P53 expression showed no significant difference between the 2 categories of carcinoma.

Antibody responses to Epstein-Barr virus, human herpesvirus 6 and human herpesvirus 7 in patients with chronic fatigue syndrome

To test for an association between chronic fatigue syndrome (CFS) and infections with Epstein-Barr virus (EBV), human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7), antibodies to these viruses were tested in the serum from three groups of individuals: (1) 10 CFS patients with chronic fatigue beginning with a clinical pattern of acute infectious mononucleosis [IM; true chronic IM (CIM)]; (2) 10 CFS patients whose illness did not start with acute IM (non-CIM), and (3) healthy controls. High EBV antibody titers were demonstrated in most patients. Antibodies to ZEBRA, a product of the immediate early EBV gene BZLF1, were detected in the serum of CFS patients at a higher frequency than in healthy controls. Antibody titers to HHV-6 and HHV-7 were also higher in the patients with CFS than in the controls. These results are consistent with the view that CFS patients may have reactivations of EBV, HHV-6 and HHV-7.

Establishment and characterization of the T-cell line, EBT-8 latently infected with Epstein-Barr virus from large granular lymphocyte leukemia

An Epstein-Barr virus (EBV) genome-positive T-cell line, designated EBT-8, was established from peripheral blood of a patient with EBV genome-positive large granular lymphocyte leukemia of T-cell origin. The cells have been cultured continuously in RPMI-1640 medium supplemented with 10% fetal calf serum and 40 U/ml interleukin-2 for more than 18 months. Analysis of T-cell receptor gene rearrangement demonstrated similar rearrangement between the fresh leukemic cells and EBT-8 cell line. The cell line has several azurophilic granules in its cytoplasm and activated cytotoxic/suppressor T-cell surface antigens (CD2, CD3, CD8, HLA-DR and T-cell receptor alpha/beta). Karyotypic analysis of the cell line showed several chromosomal abnormalities. EBV DNA was demonstrated in the cells by Southern blot hybridization and about five copies of covalently closed circular DNA per cell were detected by Gardella gel analysis. Clonotypic episomal EBV DNA was observed in the cells by Southern blot hybridization with EBV-terminal fragment probe. EBV-encoded small RNA, EBER1 were demonstrated in all cells by in situ hybridization. EBV-encoded proteins, EBNA and LMP1 were demonstrated by immunofluorescence technique. EBV activation was observed after 12-O-tetradecanoylphorbol-13- acetate treatment of the cells. These results demonstrated the establishment of a T-cell line with latent EBV genomes and suggested the involvement of EBV to the large granular lymphocyte leukemia of T cells.

Regulation of the BZLF1 promoter of Epstein-Barr virus by second messengers in anti-immunoglobulin-treated B cells

Initiation of the Epstein-Barr virus (EBV) lytic cycle is dependent on the transcription of the BZLF1 gene. The BZLF1 gene promoter (Zp) was activated by crosslinking of cell surface immunoglobulin (Ig) with anti-Ig antibody in B cells, even in the absence of other viral genes. We identified several anti-Ig response elements within Zp, which were originally defined as 12-O-tetradecanoylphorbol-13-acetate (TPA) response elements (ZI repeats and ZII, an AP-1-like domain). Since anti-Ig crosslinking leads to activation of protein kinase C (PKC) and an increase in intracellular calcium level, Zp was tested for the response to these cellular factors. Treatment with calcium ionophore A23187 increased Zp activity. When the calcium ionophore was used in conjunction with TPA, a PKC activator, the Zp induction was synergistically enhanced. 1-(5-Isoquinolinyl sulfonyl)-2-methylpiperazine, an inhibitor of PKC, inhibited the anti-Ig inducibility of Zp. Calmodulin antagonists, compound R24571 and trifluoperazine, blocked the Zp activation with anti-Ig. These findings suggest that Zp responds directly to changes in the activity of both PKC and calcium/calmodulin-dependent protein kinase. Requirement of tyrosine kinase activation for the anti-Ig-mediated Zp activation was also demonstrated through the use of the tyrosine kinase inhibitor herbimycin. These cellular gene regulatory molecules induced with anti-Ig may cooperatively play an important part in achieving efficient EBV activation as seen with anti-Ig treatment in B cells.

Epstein-Barr virus (EBV) replication and expressions of EA-D (BMRF1 gene product), virus-specific deoxyribonuclease, and DNA polymerase in EBV-activated Akata cells

The replication of Epstein-Barr virus (EBV) and the expression of EBV early proteins were studied in the Burkitt's lymphoma cell line Akata stimulated with anti-human immunoglobulin G antibody (anti-IgG). Akata cells contained approximately 20 copies of EBV genome per cell as covalently closed, circular DNA. EBV DNA replication was observed at 6 hr and reached a maximal level at 24 hr after treatment with anti-IgG. Virion DNA was found in the culture medium at 12 hr. The kinetics of expression of BMRF1 gene product (early antigen diffuse component; EA-D) paralleled that of EBV deoxyribonuclease (DNase) and of DNA polymerase. Immunoblotting analysis showed that three polypeptides with molecular masses of 54, 52, and 49 kilodaltons (kDa) were recognized as EA-D components. The EBV DNase polypeptide was detected by immunoblotting at 53 kDa. The anti-EBV DNA polymerase antibody recognized 120- and 54-kDa polypeptides in the Akata cells. Immunoprecipitation followed by immunoblotting showed that EA-D and EBV DNase polypeptides were coimmunoprecipitated with anti-EBV DNase antibody and with anti-EA-D monoclonal antibody. These findings indicate that EA-D forms a complex with EBV DNase polypeptide. The molecules of EA-D, EBV DNase, and DNA polymerase appear to be closely associated together on the EBV replication.

Detection of 5-bromo-2-deoxyuridine (BrdUrd) incorporation with monoclonal anti-BrdUrd antibody after deoxyribonuclease treatment

We studied the effects of deoxyribonucleases on the detection of 5-bromo-2-deoxyuridine (BrdUrd) by anti-BrdUrd monoclonal antibodies (mAbs). After DNase I treatment, BrdUrd was detected in cells fixed on slides with the anti-BrdUrd mAbs, B44 and BMC9318. The level of detection related to the degree of DNA digestion. DNA digestion of 25-75% resulted in levels of staining comparable to control preparations in which DNA was denatured by heating with formamide. Staining with the mAbs of DNase I-treated cells was abolished with S1 nuclease, a single-stranded DNA-specific nuclease. When exonuclease III was used after DNase I treatment, the staining intensity of cells fixed on slides increased, and BrdUrd could be detected in suspended cells by flow cytometry. Since this enzymatic method leading to the detection of BrdUrd does not involve cell loss, or destruction of either cellular morphology or epitope reactivity, as occurs with traditional DNA denaturation procedures, it is useful for kinetic studies of phenotypically mixed populations. Furthermore, staining with anti-BrdUrd mAb of cells treated with exonuclease III offers a simple approach to quantitation of apoptotic cells, in which an endogenous endonuclease is activated.

A novel early antigen associated with Epstein-Barr virus productive cycle

A murine monoclonal antibody (mAb) 92A recognized a 48-kilodalton Epstein-Barr virus (EBV) early antigen (EA). The mAb stained nuclei of EBV-activated P3HR-1, B95-8 and Akata cells in a distinctive, microgranular immunofluorescence pattern. The 92A antigen was sensitive to methanol-fixation. Expression of the 92A antigen in those cells paralleled diffuse (EA-D) and restricted (EA-R) components of EA, and viral DNA (vDNA) replication. Phosphonoacetic acid did not inhibit expression of the 92A antigen. The colocalization of 92A antigen, EA-D, and vDNA was observed in viral replication compartments of B95-8 cells. On the other hand, in P3HR-1 virus-superinfected Raji cells the percentages of 92A antigen-positive cells were at much lower levels than were EA-D and -R positive cells. Immunofluorescence staining with 92A mAb was blocked by pretreatment with EBV-positive human sera, but not with EBV-negative sera. We conclude that 92A mAb recognizes a novel EA which may function in vDNA replication.

Phosphorylation of the Epstein-Barr virus BZLF1 immediate-early gene product ZEBRA

Expression of the Epstein-Barr virus (EBV) BZLF1 gene product ZEBRA is a first step in the cascade of the virus-productive cycle. ZEBRA protein was detected by immunoblotting as a single band at 38 kDa in Akata cells after crosslinkage of membrane immunoglobulin G (IgG) with anti-IgG antibody. Immunoprecipitation of [32P]phosphate-labeled, anti-IgG-stimulated Akata cells with anti-ZEBRA antibody showed that ZEBRA was phosphorylated. Phosphoamino acid analysis demonstrated phosphorylation of serine, but not threonine or tyrosine, and tryptic-peptide mapping showed multiple phosphorylated peptides of ZEBRA. Treatment with 8-bromo cAMP and blockage of phosphodiesterase by theophylline in anti-IgG-stimulated cells increased the phosphorylation of three ZEBRA peptides. Incubation with 12-O-tetradecanoylphorbol-13-acetate (TPA) reduced the phosphorylation of these three ZEBRA peptides, while treatment with staurosporine, a protein kinase C (PKC) inhibitor, enhanced their phosphorylations. These data suggest that activation of PKC with TPA induces the ZEBRA dephosphorylation and that activation of cAMP-dependent protein kinase A enhances the ZEBRA phosphorylation at the specific sites.

Early events in Epstein-Barr virus genome expression after activation: regulation by second messengers of B cell activation

RNA transcription from the BamHI Z and BamHI R and HindIII G regions of the Epstein-Barr virus (EBV) genome was studied after treatment of Akata cells with anti-immunoglobulin G (IgG), with second messenger agonists or antagonists to determine how latent EBV activation is regulated by B cell second messengers. Northern gel analysis demonstrated that BZLF1, BZLF1 + BRLF1, and BMLF1 + BSLF2 transcripts were induced at 2 hr and increased in concentration at 4 hr after induction with anti-IgG; transcripts from BRRF1, BaRF1, BMLF1, and BMRF1 were initiated at 4 hr; a transcript from BRRF2 appeared at 6 hr. The patterns of transcription from these genes after repeated stimulations with calcium ionophore A23187 + dioctanoylglycerol paralleled those with anti-IgG except that times of initiation were delayed by about 2 hr. Nuclear run-off assay of BZLF1 gene showed rapid increases in their transcriptions from 30 to 60 min after anti-IgG treatment. The protein kinase C antagonist, staurosporine, completely blocked the appearance of these transcripts, while 8-bromo cAMP + theophylline suppressed the transcription by about 40%. The regulation of EBV activation in Akata cells with anti-IgG or with second messenger agonists or antagonists can be explained by regulation at the level of transcription of immediate-early genes of EBV.

Formation of intranuclear replication compartments of Epstein-Barr virus with redistribution of BZLF1 and BMRF1 gene products

The localizations of the Epstein-Barr virus immediate-early transcriptional activator BZLF1 protein ZEBRA, of the BMRF1 early antigen diffuse component (EA-D), and of viral DNA replication were studied in the Burkitt's lymphoma cell line Akata treated with anti-human immunoglobulin antibodies. Prompt and sequential appearance of ZEBRA, EA-D, and viral DNA was observed in about 70% of the cells. At early times after activation, ZEBRA had a diffuse intranuclear distribution, but later it was concentrated in globular regions within the nucleus. EA-D appeared first in a finely stippled pattern and then in a diffuse pattern. At late times, EA-D concentrated in globular regions similar to those with ZEBRA. Double staining for ZEBRA and EA-D revealed that ZEBRA followed the morphological changes of EA-D with a 1-2 hr delay and that both finally coalesced in the same structures, where in situ hybridization localized replicating viral DNA. The redistribution of both ZEBRA and EA-D to these compartments depended upon the replication of lytic viral DNA. These findings indicate that these globular regions are sites for viral replication and that transcription of EBV late genes may be regulated in these structures.

Intracellular localization of tyrosine kinase substrates beneath crosslinked surface immunoglobulins in B cells

Crosslinking of surface immunoglobulins (sIg) in B cells led to the accumulation of submembranal phosphotyrosine, which was followed morphologically with the PY20 antiphosphotyrosine monoclonal antibody. Phosphotyrosine was not detected before sIg crosslinking. After sIg crosslinking, phosphotyrosine-containing proteins were redistributed from scattered small clusters near the plasma membrane to a juxtanuclear region, where immunofluorescent staining decreased with time. Double immunofluorescent staining of individual cells showed accumulation of phosphotyrosine beneath crosslinked sIg molecules at the cell surface. The sIg molecules were subsequently internalized more rapidly than the phosphotyrosine-containing molecules were redistributed. Genistein, a protein tyrosine kinase (PTK) inhibitor, blocked intracellular tyrosine phosphorylations but not cell surface patching of crosslinked sIg. When polyacrylamide beads coated with anti-Ig antibodies were added to the cells, intracellular tyrosine phosphorylation occurred beneath the regions of contact with the beads. This study provides an independent line of evidence confirming recent biochemical experiments that show that crosslinking of the antigen receptor induces PTK activity in B cells, and that components of the newly described sIg complex are among the PTK substrates. The surprising finding that the bulk of the induced phosphotyrosine remains associated with crosslinked sIg for many minutes suggests a role for complex local protein interactions in phosphotyrosine-mediated signal transduction through the antigen receptor of B cells.

Effect of genistein, a tyrosine kinase inhibitor, on latent EBV activation induced by cross-linkage of membrane IgG in Akata B cells

The activation of phosphoprotein tyrosine kinases was studied in the regulation of EBV activation in Akata cells after cross-linking membrane IgG with anti-IgG. Protein tyrosine phosphorylation was induced in Akata cells after stimulation with anti-IgG, as determined by immunoblotting with the PY20 anti-phosphotyrosine mAb. The frequency of phosphotyrosine-activated cells was also measured by immunofluorescence with the PY20 antibody. Genistein, an inhibitor of tyrosine kinases, at non-cytotoxic doses blocked EBV activation, as measured in the induction of EBV Ag, EBV immediate early BZLF1 mRNA, and its protein product ZEBRA. Such inhibitions were reversed upon removing genistein from the cultures. Genistein inhibition of early Ag induction depended upon the time of addition of genistein after stimulation with anti-IgG. These findings indicate that activation of tyrosine kinase is required for EBV activation after cross-linking membrane IgG in Akata cells.

Effect of genistein, a tyrosine kinase inhibitor, on latent EBV activation induced by cross-linkage of membrane IgG in Akata B cells

The activation of phosphoprotein tyrosine kinases was studied in the regulation of EBV activation in Akata cells after cross-linking membrane IgG with anti-IgG. Protein tyrosine phosphorylation was induced in Akata cells after stimulation with anti-IgG, as determined by immunoblotting with the PY20 anti-phosphotyrosine mAb. The frequency of phosphotyrosine-activated cells was also measured by immunofluorescence with the PY20 antibody. Genistein, an inhibitor of tyrosine kinases, at non-cytotoxic doses blocked EBV activation, as measured in the induction of EBV Ag, EBV immediate early BZLF1 mRNA, and its protein product ZEBRA. Such inhibitions were reversed upon removing genistein from the cultures. Genistein inhibition of early Ag induction depended upon the time of addition of genistein after stimulation with anti-IgG. These findings indicate that activation of tyrosine kinase is required for EBV activation after cross-linking membrane IgG in Akata cells.

Relating homology between the Epstein-Barr virus BOLF1 molecule and HLA-DQw8 beta chain to recent onset type 1 (insulin-dependent) diabetes mellitus

A role for the Epstein-Barr virus in initiating Type 1 (insulin-dependent) diabetes mellitus has been proposed since Epstein-Barr virus BOLF1 (497-513) AVTPL RIFIVPPAAEY has an 11 amino acid identity with HLA-DQw8 beta (49-60) AVTPL GPPAAEY. Rabbit antisera to the BOLF1 (496-515) peptide crossreacted with the homologous DQw8 beta (44-63) peptide but not with the related DQw7 beta (44-63) peptide, which differed from the DQw8 peptide only in an ALA to ASP substitution in position 57. Antisera to DQw8 beta (49-60) reacted with the DQw8 beta (44-63) peptide and BOLF1 (496-515), but not with DQw7 beta (44-63). The antiserum to the BOLF1 peptide bound to denatured class II major histocompatibility complex beta chains from Epstein-Barr virus-transformed DQw8-positive lymphocytes in an immunoblotting analysis. Epstein-Barr virus antibodies were detected at equal frequencies and similar titres in sera of 30 patients with Type 1 diabetes (16 of 30; 63%) and in sera of 20 non-diabetic control subjects (13 of 20; 65%). Sera from diabetic patients did not bind to DQw8 beta (44-63) or BOLF1 (496-515) peptides. From these data we conclude that there is no simple relationship between serological evidence of Epstein-Barr virus infection and crossreactions between homologous Epstein-Barr virus and class II major histocompatibility complex peptides.

Inhibition of Epstein-Barr virus production in P3HR-1 cells by Epstein-Barr virus-seropositive human serum

The effect of human serum with or without Epstein-Barr virus (EBV) antibodies was characterized on virus production in P3HR-1 cells. Cell culturing with EBV-seropositive sera reduced both production of infectious virus and amounts of virion DNA in the supernatants. EBV DNA was also reduced in the cells. Such reductions in cell-associated EBV DNA depended upon the concentration of seropositive serum and incubation time. Decreased frequencies of productive EBV DNA-replicating cells were observed in cell populations which had reduced levels of cell-associated EBV DNA. The inhibitory effect of seropositive serum was reversed upon switching the cells to medium with seronegative serum. In serial sera of an acute infectious mononucleosis patient the EBV DNA-reducing activity arose in parallel to antibodies against EBV membrane antigen and nuclear antigen. Possible mechanisms were discussed for antibody-mediated inhibition of EBV production.

Activation of latent EBV via anti-IgG-triggered, second messenger pathways in the Burkitt's lymphoma cell line Akata

Anti-IgG treatment activated latent EBV genomes in 50 to 70% of the cells of the Burkitt's lymphoma cell line Akata. The EBV-activating role of intracellular Ca2+, as potentiated by diacylglycerol (DAG) and suppressed by cAMP, was analyzed in the cells through effects of agonists and antagonists of these second messenger pathways. Early Ag (EA) was induced in 10% of cells with the calcium ionophore A23187 (A23187). EA induction with anti-IgG or A23187 was blocked by a calmodulin antagonist, trifluoperazine. The DAG pathway had a potentiating but not direct effect on EBV activation because: 1) the DAG analog, dioctanoylglycerol (diC8), an agonist for protein kinase C, alone induced only 2% EA-positive cells, 2) diC8 synergized with A23187 for EA induction, and 3) the protein kinase C antagonist, staurosporine, almost completely inhibited EA induction by anti-IgG. When cells were reincubated in medium with fresh diC8 and A23187 at 3, 6, 9, and 12 h, EA induction at 24 h reached the levels seen with anti-IgG stimulation. A cAMP-mediated pathway suppressed EBV activation because dibutyryl cAMP or 8-bromo-cAMP, plus blockage of phosphodiesterase by theophylline, or use of forskolin, inhibited EA induction with anti-IgG. Although the principal stimulatory role in EBV activation of a Ca2(+)-mediated, second messenger pathway, as synergized by DAG and inhibited by cAMP, was established, we did not explain the significant lag in EA induction by A23187 and diC8 as compared with anti-IgG induction of EA. We conclude that EBV genome activation with anti-IgG is mediated by Ca2+/calmodulin and DAG pathways in Akata cells, that the cAMP pathway suppresses EA induction by anti-IgG, and that a mechanism regulating the speed of EA induction remains unexplained.

Activation of latent EBV via anti-IgG-triggered, second messenger pathways in the Burkitt's lymphoma cell line Akata

Anti-IgG treatment activated latent EBV genomes in 50 to 70% of the cells of the Burkitt's lymphoma cell line Akata. The EBV-activating role of intracellular Ca2+, as potentiated by diacylglycerol (DAG) and suppressed by cAMP, was analyzed in the cells through effects of agonists and antagonists of these second messenger pathways. Early Ag (EA) was induced in 10% of cells with the calcium ionophore A23187 (A23187). EA induction with anti-IgG or A23187 was blocked by a calmodulin antagonist, trifluoperazine. The DAG pathway had a potentiating but not direct effect on EBV activation because: 1) the DAG analog, dioctanoylglycerol (diC8), an agonist for protein kinase C, alone induced only 2% EA-positive cells, 2) diC8 synergized with A23187 for EA induction, and 3) the protein kinase C antagonist, staurosporine, almost completely inhibited EA induction by anti-IgG. When cells were reincubated in medium with fresh diC8 and A23187 at 3, 6, 9, and 12 h, EA induction at 24 h reached the levels seen with anti-IgG stimulation. A cAMP-mediated pathway suppressed EBV activation because dibutyryl cAMP or 8-bromo-cAMP, plus blockage of phosphodiesterase by theophylline, or use of forskolin, inhibited EA induction with anti-IgG. Although the principal stimulatory role in EBV activation of a Ca2(+)-mediated, second messenger pathway, as synergized by DAG and inhibited by cAMP, was established, we did not explain the significant lag in EA induction by A23187 and diC8 as compared with anti-IgG induction of EA. We conclude that EBV genome activation with anti-IgG is mediated by Ca2+/calmodulin and DAG pathways in Akata cells, that the cAMP pathway suppresses EA induction by anti-IgG, and that a mechanism regulating the speed of EA induction remains unexplained.

Synthetic peptides to identify antigenic determinants on Epstein-Barr virus gp350/220

We synthesized three peptides, MA1 - Thr19-Val28(+Tyr) -, MA2 - Ser807-Ala816-, and MA3-Ser718-Glu729(+Tyr) from the sequence of Epstein-Barr virus gp350/220 and immunized rabbits with these peptides. Rabbit antisera to the peptides had antipeptide radioimmunoassay titers of 1:400 for anti-MA1, 1:200 for anti-MA2, and 1:1600 for anti-MA3. The anti-MA1 serum recognized gp350/220 in Western blotting to SDS-electrophoresed proteins from 12-O-tetradecanoylphorbol-13-acetate- and n-butyrate-treated B95-8 cells, but anti-MA2 and MA3 sera did not. None of the sera reacted with gp350/220 by membrane or cytoplasmic immunofluorescence or by immunoprecipitation of Triton X-100 solubilized proteins.

Intracellular synthesis of Epstein-Barr virus membrane antigen gp350/220. Inhibitory effect of monensin on its expression

We have defined the intracellular expression and localization of gp350/220, one of the Epstein-Barr virus (EBV) induced membrane antigens, on 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and n-butyrate-treated P3HR-1 cells. 1B6 monoclonal antibody (mAb) immunoprecipitated gp350/220 from [35S]-methionine-labeled cells, as confirmed with other mAbs (2L10, 72A1, and C1), to the same membrane antigen. The appearance of gp350/220 was observed about 14 h after TPA and n-butyrate activation and reached a maximal level at about 48 h. 1B6 mAb membrane immunofluorescence-positive and cytoplasmic fluorescence-positive cells appeared progressively in cell populations at the same frequencies. Cytoplasmic immunofluorescent staining with 1B6 mAb demonstrated a paranuclear complex which was identical to a rhodamine-labeled wheat germ agglutinin-stained pattern which has been ascribed to the Golgi apparatus. We investigated the effect of monensin on gp350/220 expression and processing. Monensin at 10(-7) M significantly inhibited membrane antigen expression in the Golgi apparatus and on the cell surface, but had a negligible effect on synthesis of viral capsid antigen, early antigen, and viral DNA. The inhibition of gp350/220 with monensin was further characterized by the immunoprecipitation of gp350/220 with anti-MA-positive human sera and mAbs. Monensin treatment resulted in the accumulation of a 165-kD molecule which was judged to be a precursor of gp350/220. These results were consistent with the view that the Golgi apparatus plays an important role as a place of synthesis, processing, and maturation of gp350/220.

Inhibition of Epstein-Barr virus (EBV) release from P3HR-1 and B95-8 cell lines by monoclonal antibodies to EBV membrane antigen gp350/220

Antibody-mediated inhibition of Epstein-Barr virus (EBV) release from the EBV-productive cell lines P3HR-1 and B95-8 was probed with two monoclonal antibodies (MAbs), 72A1 and 2L10, which immunoprecipitated the same EBV membrane antigen (MA) gp350/220 found with the 1B6 MAb with which inhibition of EBV release from P3HR-1 cells was first described. These three MAbs were not equivalent in either MA reactivities or functional effects, reflecting the variable expression of different epitopes of gp350/220. 1B6 recognized MA on P3HR-1 cells, which expressed predominately the gp220 form of MA. 1B6 did not recognize (or barely recognized) a determinant on B95-8 cells. MAbs 2L10 and 72A1 reacted as well with B95-8 cells as they did with P3HR-1 cells. MAbs 1B6 and 2L10 neutralized neither P3HR-1 nor B95-8 virus, but 72A1 neutralized both viruses. MAbs 1B6 and 72A1 inhibited P3HR-1 virus release, as measured by the assay for infectious virus and by DNA hybridization analysis of released virus, but 2L10 had no such activity. 72A1 (but not 1B6) inhibited release of EBV from B95-8 cells. These experiments pointed to the presence of three different epitopes on gp350/220, identified with the respective MAbs and having varying involvement in virus neutralization and virus release inhibition.

Immune response to intermediate filament-associated, Epstein-Barr virus-induced early antigen

A murine monoclonal antibody (MAb) (15TD3) was found to recognize a unique filamentous structure in Epstein-Barr virus (EBV)-producing lymphoblastoid cell lines. By immunofluorescent morphology, in comparison with a control MAb to vimentin, the 15TD3 filamentous structure was judged to be associated with intermediate filaments of the cytoskeleton. Expression of the 15TD3 antigen and vimentin was induced simultaneously in some EBV genome-positive cell lines either by EBV superinfection or by 12-0-tetradecanoyl-1-phorbol-13-acetate (TPA) and n-butyrate treatment. The 15TD3 antigen was considered to be a restricted component of the EBV-induced early antigen (EA) complex. The 15TD3 antigen was expressed only in EBV genome-activated cells after either spontaneous EBV genome activation, EBV superinfection, or TPA and n-butyrate treatment. The expression of 15TD3 antigen paralleled the induction of EA in several models of induction of EBV antigens, and was detected only in EA+ cells which were stained with anti-EA+ human sera. The reactivity of 15TD3 MAb was blocked with anti-EA+ human serum, but not with anti-EA- serum. The synthesis of 15TD3 antigen was not inhibited with phosphonoacetic acid, was resistant to acetone fixation, and was sensitive to ethanol (or methanol) fixation. Human lymphoblastoid cells from patients with acute infectious mononucleosis were cloned for the production of antibodies which detected EBV-specific or -nonspecific epitopes on filamentous structures. Two human MAb were defined by two-color immunofluorescence to react to the 15TD3 determinants on intermediate filaments of EBV+ cells. This study supports the following views: that EBV genome activation induces a structure associated with intermediate filaments, and that antibodies against both the EBV-specific, intermediate filament-associated epitope and native intermediate filament epitopes are produced by some EBV-transformed lymphoblastoid cell lines from patients with infectious mononucleosis.

Immune response to intermediate filament-associated, Epstein-Barr virus-induced early antigen

A murine monoclonal antibody (MAb) (15TD3) was found to recognize a unique filamentous structure in Epstein-Barr virus (EBV)-producing lymphoblastoid cell lines. By immunofluorescent morphology, in comparison with a control MAb to vimentin, the 15TD3 filamentous structure was judged to be associated with intermediate filaments of the cytoskeleton. Expression of the 15TD3 antigen and vimentin was induced simultaneously in some EBV genome-positive cell lines either by EBV superinfection or by 12-0-tetradecanoyl-1-phorbol-13-acetate (TPA) and n-butyrate treatment. The 15TD3 antigen was considered to be a restricted component of the EBV-induced early antigen (EA) complex. The 15TD3 antigen was expressed only in EBV genome-activated cells after either spontaneous EBV genome activation, EBV superinfection, or TPA and n-butyrate treatment. The expression of 15TD3 antigen paralleled the induction of EA in several models of induction of EBV antigens, and was detected only in EA+ cells which were stained with anti-EA+ human sera. The reactivity of 15TD3 MAb was blocked with anti-EA+ human serum, but not with anti-EA- serum. The synthesis of 15TD3 antigen was not inhibited with phosphonoacetic acid, was resistant to acetone fixation, and was sensitive to ethanol (or methanol) fixation. Human lymphoblastoid cells from patients with acute infectious mononucleosis were cloned for the production of antibodies which detected EBV-specific or -nonspecific epitopes on filamentous structures. Two human MAb were defined by two-color immunofluorescence to react to the 15TD3 determinants on intermediate filaments of EBV+ cells. This study supports the following views: that EBV genome activation induces a structure associated with intermediate filaments, and that antibodies against both the EBV-specific, intermediate filament-associated epitope and native intermediate filament epitopes are produced by some EBV-transformed lymphoblastoid cell lines from patients with infectious mononucleosis.

Hyperexpressed hairy leukemic cell Ii might bind to the antigen-presenting site of class II MHC molecules

The p35 protein which is hyperexpressed on hairy leukemic cells was determined to be Ii, the electrophoretically invariant glycoprotein that is associated with class II major histocompatibility complex (Ia) antigens from the time of their synthesis. The principal function of class II MHC antigens is to present to T cell receptors those digested foreign antigenic peptides that probably fold as amphipathic alpha-helices and adsorb to a hydrophobic surface (desetope) on Ia. By a novel strip-of-helix hydrophobicity algorithm we found that the sequence Leu-142 to His-170 in Ii formed a five-cycle, amphipathic, alpha-helix, the highest scoring one among a series of proteins commonly used as experimental antigens. This finding led to the hypothesis that this sequence in Ii bound to the antigen-binding site (desetope) of Ia until release and self-aggregation in the endosome in order that digested foreign peptides could then bind to Ia. Abundant expression of Ii in leukemic cells might be associated with an altered capacity of those cells to present foreign or leukemic antigens to the host's immune system.

Epstein-Barr virus-specific cytoskeletal early antigen in EBV-transformed cell lines

An Epstein-Barr virus (EBV)-specific determinant of early antigen (EA) character was found to be associated with intermediate filaments of EBV genome-activated cells. This determinant was defined with a murine monoclonal antibody (MAb) and with human MAb derived from lymphoblastoid cell lines of patients with acute infectious mononucleosis (IM). Such patients' antibodies either recognized intermediate filament determinants in general, or were restricted to the intermediate filament determinant of EBV genome-activated cells, as also recognized with the 1B6 murine MAb. The 1B6 determinant was a component of EA as defined by phosphonoacetate-resistance, methanol-sensitivity, and various co-staining and antibody-blocking experiments. While anti-intermediate filament antibodies have been reported after various viral illnesses, the 1B6 and some patients' antibodies recognize an EBV-specific determinant which might function in the lytic cycle of these cells.