Epstein-Barr Virus Lytic Cycle Research Articles

The lytic cycle of Epstein-Barr virus is associated with decreased expression of cell surface major histocompatibility complex class I and class II molecules.

Human herpesviruses utilize an impressive range of strategies to evade the immune system during their lytic replicative cycle, including reducing the expression of cell surface major histocompatibility complex (MHC) and immunostimulatory molecules required for recognition and lysis by virus-specific cytotoxic T cells. Study of possible immune evasion strategies by Epstein-Barr virus (EBV) in lytically infected cells has been hampered by the lack of an appropriate permissive culture model. Using two-color immunofluorescence staining of cell surface antigens and EBV-encoded lytic cycle antigens, we examined EBV-transformed B-cell lines in which a small subpopulation of cells had spontaneously entered the lytic cycle. Cells in the lytic cycle showed a four- to fivefold decrease in cell surface expression of MHC class I molecules relative to that in latently infected cells. Expression of MHC class II molecules, CD40, and CD54 was reduced by 40 to 50% on cells in the lytic cycle, while no decrease was observed in cell surface expression of CD19, CD80, and CD86. Downregulation of MHC class I expression was found to be an early-lytic-cycle event, since it was observed when progress through late lytic cycle was blocked by treatment with acyclovir. The immediate-early transactivator of the EBV lytic cycle, BZLF1, did not directly affect expression of MHC class I molecules. However, BZLF1 completely inhibited the upregulation of MHC class I expression mediated by the EBV cell-transforming protein, LMP1. This novel function of BZLF1 elucidates the paradox of how MHC class I expression can be downregulated when LMP1, which upregulates MHC class I expression in latent infection, remains expressed in the lytic cycle.

Lymphoproliferation in children after liver transplantation.

Lymphoproliferation in children after liver transplantation.

Interaction with the Epstein-Barr virus helicase targets Zta to DNA replication compartments.

Zta has a dual role in the Epstein-Barr virus (EBV) lytic cycle, acting as a key regulator of EBV lytic gene expression and also being essential for lytic viral DNA replication. Zta's replication function is mediated in part through interactions with the core viral replication proteins. We now show interaction between Zta and the helicase (BBLF4) and map the binding region to within amino acids (aa) 22 to 86 of the Zta activation domain. In immunofluorescence assays, green fluorescent protein (GFP)-tagged BBLF4 localized to the cytoplasm of transfected cells. Cotransfection of Zta resulted in translocation of BBLF4-GFP into the nucleus indicating interaction between these two proteins. However, Zta with a deletion of aa 24 to 86 was unable to mediate nuclear translocation of BBLF4-GFP. Results obtained with Zta variants carrying deletions across the aa 24 to 86 region indicated more than one contact site for BBLF4 within this domain, and this was reinforced by the behavior of the four-point mutant Zta (m22/26,74/75), which was severely impaired for BBLF4 interaction. Binding of BBLF4 to Zta was confirmed using GST affinity assays. In both cotransfection-replication assays and replication assays performed in EBV-positive P3HR1 cells, the Zta (m22/26,74/75) mutant was replication defective. In Zta-transfected D98-HR1 cells, replication compartments could be detected by immunofluorescence staining using anti-BMRF1 monoclonal antibody. Cells transfected with Zta variants that were defective for helicase binding still formed replication compartments, but Zta was excluded from these compartments. These experiments reveal a role for the Zta-helicase interaction in targeting Zta to sites of viral DNA replication.

Activation of the BRLF1 promoter and lytic cycle of Epstein-Barr virus by histone acetylation.

Histone acetylation alters the chromatin structure and activates the genes that are repressed by histone deacetylation. This investigation demonstrates that treating P3HR1 cells with trichostatin A (TSA) activates the Epstein-Barr virus (EBV) lytic cycle, allowing the virus to synthesize three viral lytic proteins-Rta, Zta and EA-D. Experimental results indicate that TSA and 12-O:-tetradecanoylphorbol-13-acetate synergistically activate the transcription of BRLF1, an immediate-early gene of EBV. Chromatin immunoprecipitation assay reveals that histone H4 at the BRLF1 promoter is acetylated after P3HR1 cells are treated with TSA, suggesting that histone acetylation activates BRLF1 transcription. Furthermore, results in this study demonstrate that mutation of a YY1-binding site in the BRLF1 promoter activates BRLF1 transcription 1.6- and 2.3-fold in P3HR1 cells and C33A cells, respectively. Real time PCR analysis reveals that the mutation also increases the histone acetylation level of the nucleosomes at the BRLF1 promoter 1. 64- and 3.08-fold in P3HR1 and C33A cells, respectively. Results presented herein suggest that histone deacetylation plays an important role in maintaining the viral latency and histone acetylation at the BRLF1 promoter allows the virus to express Rta and to activate the viral lytic cycle.

The late lytic LMP-1 protein of Epstein-Barr virus can negatively regulate LMP-1 signaling.

The BNLF-1 open reading frame of Epstein-Barr virus (EBV) encodes two related proteins, latent membrane protein-1 (LMP-1) and lytic LMP-1 (lyLMP-1). LMP-1 is a latent protein required for immortalization of human B cells by EBV, whereas lyLMP-1 is expressed during the lytic cycle and is found in the EBV virion. We show here that, in contrast to LMP-1, lyLMP-1 is stable, with a half-life of >20 h in tetradecanoyl phorbol acetate- and butyrate-treated B95-8 cells. Although lyLMP-1 itself has negligible effects on NF-kappaB activity, it inhibits NF-kappaB activation by LMP-1 in a dose-dependent manner. The lyLMP-1 protein does not oligomerize with LMP-1, and the negative effect of lyLMP-1 on NF-kappaB activation by LMP-1 does not result from lyLMP-1-mediated disruption of LMP-1 oligomers. Modulation of LMP-1-activated signaling pathways is the first identified biological activity associated with lyLMP-1, and this activity may contribute to the progression of EBV's lytic cycle.

High In-Vitro Antitumour Activity of Triphenyltin Coumarin 3‐Carboxylate and its Coordination Complexes With Monodentate Oxygen Donor Ligands Against the Epstein Barr Virus (EBV)‐DNA Positive Raji and the P‐388 Murine Leukaemia Cell Lines, and Evidence for the Suppression by Organotin of the Early Antigen Complex in the EBV Lytic Cycle

Triphenyltin coumarin-3-carboxylate and its coordination complexes with ethanol, triphenylphosphine oxide, triphenylarsine oxide, diphenylcyclopropenone and quinoline N-oxide exhibited high in vitro cytotoxicity (LC50 values in the range 0.25-3.4 μg/mL) when tested against EBV-DNA positive Raji cells and P-388 leukaemia cells, compared to the standard drug 5-Fluorouracil, which showed LC50 values of 11 and >50 μg/mL, respectively, against these cells. Additional tests performed on the Raji cells incubated with the quinoline N-oxide complex in the presence of the tumour promoters, TPA and sodium butyrate, revealed that the diffused and restricted protein components of the early antigen complex were suppressed relative to the control containing only the promoters, indicating impaired function of the genes involved as transactivators in the early lytic cycle of the EBV. The failure of the restriction enzymes Eco R1 and Hind III to cleave the extracted DNA from such treated cells in contrast to the control, coupled with the amplification of the BMLF-1 gene by the PCR technique which was realised only with the DNA of the control and not of the treated sample, point to a punitive interaction of the organotin with the nuclear DNA of the Raji cells.

Specificity of T cells in synovial fluid: high frequencies of CD8(+) T cells that are specific for certain viral epitopes.

CD8+ T cells dominate the lymphocyte population insynovial fluid in chronic inflammatory arthritis. It is known that theseCD8+ T cells are often clonally or oligoclonally expanded, but theirspecificity and their relevance to the pathogenesis of joint disease hasremained unclear. We found that as many as 15.5% of synovial CD8+ Tcells may be specific for a single epitope from an Epstein-Barr virus lyticcycle protein. The virus-specific T cells within the joint showed increasedexpression of markers of activation and differentiation compared with those inthe periphery, and retained their functional capacity to secreteproinflammatory cytokines on stimulation. These activated, virus-specificCD8+ T cells could therefore interact with synoviocytes, either bycell-cell contact or by a cytokine network, and play a 'bystander'role in the maintenance of inflammation in patients with arthritis.

Role of the epstein-barr virus RTA protein in activation of distinct classes of viral lytic cycle genes.

Initiation of the Epstein-Barr virus (EBV) lytic cycle is controlled by two immediate-early genes, BZLF1 and BRLF1. In certain epithelial and B-cell lines, their protein products, ZEBRA and Rta, stimulate their own expression, reciprocally stimulate each other's expression, and activate downstream viral targets. It has been difficult to examine the individual roles of these two transactivators in EBV-infected lymphocytes, as they are expressed simultaneously upon induction of the lytic cycle. Here we show that the Burkitt lymphoma cell line Raji represents an experimental system that allows the study of Rta's role in the lytic cycle of EBV in the absence and presence of ZEBRA. When expressed in Raji cells, exogenous Rta does not activate endogenous BZLF1 expression, yet Rta remains competent to transactivate certain downstream viral targets. Some genes, such as BaRF1, BMLF1, and a late gene, BLRF2, are maximally activated by Rta itself in the absence of detectable ZEBRA. The use of the Z(S186A) mutant form of ZEBRA, whose transactivation function is manifest only by coexpression of Rta, allows identification of a second class of lytic cycle genes, such as BMRF1 and BHRF1, that are activated in synergy by Rta and ZEBRA. It has already been documented that of the two activators, only ZEBRA stimulates the BRLF1 gene in Raji cells. Thus, there is a third class of viral genes activated by ZEBRA but not Rta. Moreover, ZEBRA exhibits an inhibitory effect on Rta's capacity to stimulate the late gene, BLRF2. Consequently ZEBRA may function to repress Rta's potential to activate some late genes. Raji cells thus allow delineation of the combinatorial roles of Rta and ZEBRA in control of several distinct classes of lytic cycle genes.

Tobacco-induced activation of the epstein-barr virus lytic cycle

Tobacco-induced activation of the epstein-barr virus lytic cycle

Definition of the transcription factors which bind the differentiation responsive element of the Epstein-Barr virus BZLF1 Z promoter in human epithelial cells.

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus and an important human pathogen. Initiation of the EBV lytic cycle is dependent upon transcription of the EBV BZLF1 gene. Our previous studies of transcriptional regulation of the BZLF1 Z promoter (Zp) in human SCC12F epithelial cells identified a region within Zp that is responsive to epithelial cell differentiation. In the present study, we localize this differentiation responsive element to the CREB/AP-1-like binding site (TGACATCA) between -67 to -60 bp within Zp, previously designated ZII, and furthermore show that homodimers and heterodimers of CREB and ATF-1 specifically bind ZII. Consistent with a regulatory role for CREB and ATF-1 in differentiation dependent BZLF1 expression, ZII was able to bind approximately 3-fold more CREB and ATF-1 when incubated with nuclear extract obtained from populations of SCC12F cells enriched for the differentiated phenotype than when incubated with extract obtained from populations enriched for the undifferentiated phenotype. In addition, CREB and ATF-1 were found to increase in abundance during SCC12F differentiation. These results indicate a regulatory role for CREB and ATF-1 in differentiation-dependent expression of BZLF1 in human epithelial cells.

The detection of Epstein-Barr virus DNA in lung tissue from patients with idiopathic pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a clinical syndrome in which the precipitating factors are unclear. An association between Epstein-Barr Virus (EBV) and IPF had previously been suggested using serology and immunohistochemistry. This study sought confirmation of the presence of EBV DNA in the lung tissue of patients with IPF. Lung tissue obtained surgically from 27 patients with IPF and 28 control subjects was investigated for the presence of EBV by immunohistochemistry and polymerase chain reaction (PCR) analysis. Immunohistochemistry used antibodies specific for EBV lytic cycle antigens (gp340/220 and VCA). Nested PCR analysis used oligonucleotide primers specific for EBV and was sensitive to one copy of EBV DNA. Twelve of the 27 patients with IPF (44%) and three of the 28 control subjects (10%) were EBV positive by immunohistochemistry (p = 0.005). Thirteen of the patients with IPF (48%) and four of the control subjects (14%) were EBV positive by PCR (p = 0.007). Eleven of the patients with IPF (41%) and none of the control subjects were EBV positive by both immunohistochemistry and PCR (p = < 0.001). These data further suggest an association between EBV and IPF. In addition it defines a novel method for detecting EBV in lung tissue. EBV may be involved in the pathogenesis of the disease; however, further studies are required to establish a causal relationship.

Role of Rta in the translation of bicistronic BZLF1 of Epstein-Barr virus.

The BZLF1 gene of Epstein-Barr virus (EBV), which encodes a transcription factor, Zta, is transcribed into monocistronic and bicistronic mRNAs from two different promoters during the immediate-early stage of the EBV lytic cycle. It is generally accepted that the Zta protein translated from the monocistronic mRNA profoundly influences the activation of the EBV lytic cycle. In this study, we constructed a plasmid, pCMV-RZLUC, which can transcribe a bicistronic mRNA consisting of BRLF1 and a BZLF1-luc fusion gene under latent conditions. P3HR1 cells transfected with this plasmid produce a luciferase activity which is approximately 17-fold higher than the activity exhibited by pRZLUC, a plasmid incapable of transcribing the bicistronic mRNA. Genetic analyses indicated that mutations in BRLF1 not only can decrease the translation of the fusion gene from the bicistronic mRNA but can also be complemented by a functional BRLF1 gene in cis. This observation implies that the product of BRLF1, Rta, is involved in the translation of the downstream gene. Results presented herein also demonstrate that these mutations cannot be complemented in trans with a plasmid overexpressing Rta, suggesting that the amount of Rta in the vicinity of the intercistronic region may be crucial for the translation. Furthermore, our results correspond to those of previous investigations indicating that the Zta protein can be translated from the bicistronic mRNA and that, similar to the translation of bicistronic ZLUC, mutations in BRLF1 also hinder the translation of Zta from the BRLF1-BZLF1 bicistronic mRNA. Translation of Zta from the bicistronic mRNA may play an essential role in the activation of the EBV lytic cycle.

Amino-acid change in the Epstein-Barr-virus ZEBRA protein in undifferentiated nasopharyngeal carcinomas from Europe and North Africa.

Different Epstein-Barr-virus(EBV) variants were found to be associated with nasopharyngeal carcinoma (NPC). The type-C variant lacks the BamHI site between the BamHI W1* and I* regions and the type-f variant has an extra BamHI site in the BamHI F fragment. The BNLF1 gene (which encodes the LMP1 protein) from a nude-mouse-passaged CAO strain and from NPC biopsies from Taiwanese patients also exhibits variations resulting in structural and functional differences in the protein. The BZLF1 gene encodes the ZEBRA protein which triggers the EBV lytic cycle. A difference has been observed in 8 amino acids in the ZEBRA sequence in B95-8 (Z95) and P3HR1 (ZP3) cell lines. EBV found in NPC biopsies and peripheral-blood cells from Asians was predominantly of the ZP3 type (72%), while 81% of samples from different EBV-associated diseases and peripheral-blood cells from North Africa or Europe were of the Z95 type. We found that an alanine 206 had been replaced by a serine in the Z95 sequence in 72% of the NPC biopsies from European and North African patients. The Zser206 variant is found in a significantly lower percentage (p < 0.001) of other EBV-positive tissues from individuals in the same region (10-33%). In contrast, a 30-bp deletion is observed near the 3' end of the LMP1 gene in the majority of EBV (86%) from NPC and peripheral-blood cells from Asians, whereas a significantly lower percentage (p < 0.001) of NPC biopsies from European and North African patients (56%) have this deletion, as do lymphocytes from control individuals from the same region (36 and 55% respectively).

BHRF1, a viral homologue of the Bcl-2 oncogene, is conserved at both the sequence and functional level in different Epstein-Barr virus isolates.

BHRF 1, a component of the restricted early antigen (EA) complex of the Epstein-Barr virus (EBV) lytic cycle, encodes a 17 kDa putative transmembrane protein with both sequence and functional homology to the Bcl-2 proto-oncogene. To determine whether there was any sequence variation over the BHRF1 open reading frame (ORF), 15 EBV isolates from different geographical regions and from both healthy donors and patients with EBV-associated diseases were sequenced. A small number of base changes which resulted in amino acid substitutions in the BHRF1 protein were found relative to the prototype B95.8 EBV sequence and these were predominantly clustered near the amino terminus of the BHRF1 protein outside conserved domains identified in the Bcl-2 homologues. In transient transfection assays none of the mutations in the BHRF1 ORF from eight different EBV isolates had a significant effect on BHRF1 protein localization compared to the B95.8 BHRF1 protein. However, transient expression of the adenovirus 12 19K protein or Bcl-2 resulted in localization patterns distinct from that observed with BHRF1 protein. Whilst all eight EBV isolates and E1B-19K gave comparable levels of protection to the DNA-damaging agent cis-platin, Bcl-2 did not afford significant protection. Thus, despite several amino acid changes in the BHRF1 ORF of some of the EBV isolates studied, the ability of the protein to protect against cis-platin induced apoptosis is conserved. The highly conserved nature of BHRF1 amongst different EBV isolates at both the sequence and functional level supports the proposed important role of BHRF1 in delaying cell death, thereby maximizing the production of progeny virus and facilitating the establishment of virus persistence.

Early Detection of the Lytic LMP-1 Protein in EBV-Infected B-Cells Suggests Its Presence in the Virion

The Epstein–Barr virus (EBV)-positive B958 cell line expresses two related membrane proteins encoded by BNLF-1 open reading frames. One protein (LMP-1) has been shown to be essential for the growth transforming properties of EBV. The second protein (the lytic LMP-1) is an amino-terminally truncated form of LMP-1 whose expression is associated with induction of EBV's lytic cycle. We have investigated the expression of full-length and lytic forms of LMP-1 immediately after infection of the EBV-negative, B-lymphoma cell line BJAB. Only the lytic LMP-1 protein is present in BJAB cells early (within minutes following addition of virus) after infection with virus derived from either uninduced or tetradecanoyl phorbol acetate and sodium butyrate-induced B958 cells. Lytic LMP-1 protein levels begin to decline by 48 hr after infection, whereas levels of full-length LMP-1 increase between 24 and 48 hr after infection and then remain constant. The presence of the lytic LMP-1 protein in infected cells is independent of both protein synthesis and virus internalization. We also find the lytic LMP-1 protein in BJAB cells early after infection (within 3 hr of addition of virus) with the HH514 strain of EBV, and HH514 cells treated with tetradecanoyl phorbol acetate and sodium butyrate, express high levels of both the lytic LMP-1 and full-length LMP-1 proteins. The lytic LMP-1 protein is enriched in purified virion preparations, and immunoelectron microscopic analysis indicates that EBV virions can be specifically labeled with anti-LMP-1 antisera. Together, these results are consistent with a model in which the lytic LMP-1 protein is present in the EBV virion and is carried into the B-cell upon infection and suggest a role for this protein in early infection events and/or in EBV's lytic cycle.

Epstein-Barr virus BHRF1 protein protects intestine 407 epithelial cells from apoptosis induced by tumor necrosis factor alpha and anti-Fas antibody.

Tumor necrosis factor (TNF) and cytotoxic T lymphocytes, which utilize Fas to induce apoptosis in target cells, are known to play a critical role in the host defense against viral infection. In this study, the Epstein-Barr virus BHRF1 protein was stably expressed in intestine 407 cells which were susceptible to cell death mediated through both the TNF receptor and Fas. WST-1 conversion assays and acridine orange staining showed that vector-transfected control cells were killed by TNF-alpha or anti-Fas antibody in a dose-dependent manner, whereas BHRF1-expressing cells were resistant to apoptosis induced by these mediators. DNA fragmentation, a characteristic of apoptosis induced by TNF-alpha and the anti-Fas antibody, was suppressed in BHRF1-expressing cells. These results indicate that the BHRF1 protein protects cells from apoptosis mediated by the TNF receptor and Fas. The role of BHRF1 as an inhibitor of cytokine-induced apoptosis during the Epstein-Barr virus lytic cycle in vivo is discussed.

Alteration of a single serine in the basic domain of the Epstein-Barr virus ZEBRA protein separates its functions of transcriptional activation and disruption of latency.

The ZEBRA protein from Epstein-Barr virus (EBV) activates a switch from the latent to the lytic expression program of the virus. ZEBRA, a member of the bZIP family of DNA-binding proteins, is a transcriptional activator capable of inducing expression from viral lytic cycle promoters. It had previously been thought that ZEBRA's capacity to disrupt EBV latency resided primarily in its ability to activate transcription of genes that encode products required for lytic replication. We generated a point mutant of ZEBRA, Z(S186A), that was not impaired in its ability to activate transcription; however, this mutation abolished its ability to initiate the viral lytic cascade. The mutant, containing a serine-to-alanine substitution in the DNA-binding domain of the protein, bound to several known ZEBRA-binding sites and activated transcription from reporters bearing known ZEBRA-responsive promoters but did not disrupt latency in EBV-infected cell lines. Therefore, initiation of the EBV lytic cycle by the ZEBRA protein requires a function in addition to transcriptional activation; a change of serine 186 to alanine in the DNA-binding domain of ZEBRA abolished this additional function and uncovered a new role for the ZEBRA protein in disruption of EBV latency. The additional function that is required for initiation of the lytic viral life cycle is likely to require phosphorylation of serine 186 of the ZEBRA protein, which may influence either DNA recognition or transcriptional activation of lytic viral promoters in a chromatinized viral episome.

Binding of the Ubiquitous Cellular Transcription Factors Sp1 and Sp3 to the ZI Domains in the Epstein–Barr Virus Lytic Switch BZLF1 Gene Promoter

Induction of the Epstein–Barr virus lytic cycle in latently infected B cells requires the expression of the immediate-early lytic gene BZLF1. We have previously identified severalcis-elements within the BZLF1 promoter that are required for induction by known inducers of the lytic cycle [E. Flemington and S.H. Speck (1990)J. Virol.64, 1217–1226]. These include four elements termed the ZI domains (ZIA, ZIB, ZIC, and ZID) that share extensive homology and that have recently been shown to bind several cellular transcription factors [A. M. Borras, J.L. Strominger, and S.H. Speck (1996)J. Virol.70, 3894–3901]. Here Sp1 and Sp3 are identified as the cellular factors present in crude B cell nuclear extract preparations that bind to the ZIC domain. In addition, three of the four complexes observed in electrophoretic mobility shift analyses employing probes containing either the ZIA or the ZID domains also represent Sp1 or Sp3 binding. Binding of Sp1 and Sp3 to the ZI domains was shown to be significantly weaker than binding of these factors to a consensus Sp1 site. A heterologous promoter construct containing three repeats of a consensus Sp1 site, cloned upstream of a single copy of the ZII (CREB/AP1) element from the BZLF1 promoter linked to the β-globin TATA box, exhibited phorbol ester inducibility. The latter observation was consistent with the functional behavior exhibited by a heterologous promoter construct containing multiple copies of the ZIC domain liked to the ZII element. However, the basal activity of the heterologous promoter construct driven by the consensus Sp1 sites was ca. 10-fold higher than that of the heterologous reporter construct containing multimerized ZIC sites. Thus, the low affinity of Sp1 binding to the ZI domains may contribute to the low-level basal activity of the BZLF1 promoter.

Cyclosporin A-sensitive induction of the Epstein-Barr virus lytic switch is mediated via a novel pathway involving a MEF2 family member.

Induction of the Epstein-Barr virus (EBV) lytic cycle by crosslinking surface immunoglobulin is inhibited by the immunosuppressants cyclosporin A (CsA) and FK506. This correlates with the ability of CsA to inhibit Ca2+-dependent transcription of the lytic cycle switch gene BZLF1. It is shown here that CsA sensitivity maps to three sites (ZIA, ZIB and ZID) that bind the serum response factor-related protein MEF2D. A synthetic promoter containing multiple copies of a MEF2D site from Zp, in conjunction with a CREB/AP-1 site (ZII) from Zp, exhibits CsA-sensitive inducibility. Furthermore, the Zp MEF2D sites were functionally interchangeable with MEF2 sites derived from heterologous promoters. While no evidence of a NFAT family member binding to either the MEF2 or CREB/AP-1 sites was obtained, it could be demonstrated that CsA-sensitive induction of Zp was mediated by calcineurin and NFATc2 in synergy with either phorbol ester or especially with the EBV-induced Ca2+/calmodulin-dependent kinase type IV/Gr. These studies identify Zp as prototypic of a novel class of CsA-sensitive and NFAT-dependent promoters defined by the presence of MEF2 sites.

An Epstein-Barr virus-associated superantigen.

More than 90% of adults are latently infected with Epstein-Barr virus (EBV), the causative agent of infectious mononucleosis, a self-limiting lymphoproliferative disease characterized by extensive T cell activation. Reactivation of this herpesvirus during immunosuppression is often associated with oncogenesis. These considerations led us to analyze the early events that occur after exposure of the immune system to EBV. Strong major histocompatibility complex (MHC) class II-dependent but not MHC-restricted, T cell proliferation was observed in vitro in response to autologous, lytically infected EBV-transformed B cells. By measuring the appearance of the early activation marker CD69 on individual T cell V beta subsets, we could demonstrate selective activation of human V beta 13- T cells. This was confirmed with murine T cell hybridomas expressing various human BV genes. While EBV- Burkitt's lymphoma cells were nonstimulatory, they induced V beta-restricted T cell activation after EBV infection. EBV specific activation was also demonstrated in cord blood cells, excluding a recall-antigen response. Thus, all of the characteristics of a superantigen-stimulated response are seen, indicating that induction of the EBV lytic cycle is associated with the expression of a superantigen in B cells. A model is presented proposing a role for the superantigen in infection, latency, and oncogenesis.