An EBV membrane protein expressed in immortalized lymphocytes transforms established rodent cells

B-cell proliferation and induction of early G1-regulating proteins by Epstein-Barr virus mutants conditional for EBNA2

Infection of primary B-lymphocytes by Epstein-Barr virus (EBV) leads to growth transformation of these B-cells in vitro. EBV nuclear antigen 2 (EBNA2), one of the first genes expressed after EBV infection of B-cells, is a transcriptional activator of viral and cellular genes and is essential for the transforming potential of the virus. We generated conditional EBV mutants by expressing EBNA2 as chimeric fusion protein with the hormone binding domain of the estrogen receptor on the genetic background of the virus. Growth transformation of primary normal B-cells by mutant virus resulted in estrogen-dependent lymphoblastoid cell lines expressing the chimeric EBNA2 protein. In the absence of estrogen about half of the cells enter a quiescent non-proliferative state whereas the others die by apoptosis. EBNA2 is thus required not only for initiation but also for maintenance of transformation. Growth arrest occurred at G1 and G2 stages of the cell cycle, indicating that functional EBNA2 is required at different restriction points of the cell cycle. Growth arrest is reversible for G1/G0 cells as indicated by the sequential accumulation and modification of cell cycle regulating proteins. EBV induces the same cell cycle regulating proteins as polyclonal stimuli in primary B-cells. These data suggest that EBV is using a common pathway for B-cell activation bypassing the requirement for antigen, T-cell signals and growth factors.

Epstein-Barr virus-associated non-Hodgkin's lymphoma in HIV-infected patients

Epstein-Barr virus (EBV) has been implicated in the pathogenesis of many lymphoproliferations arising in diverse settings, including HIV-infection. The precise roles of EBV may differ between these settings. For example, both the frequencies of EBV-association and the specific c-MYC translocations differ between sporadic and African Burkitt's lymphoma. Similarly, the frequencies of EBV-association in HIV-infected patients differs between anatomical sites, types of NHL, and geographic locations. HIV-related NHL have genetic alterations similar to NHL arising in the general population, and have less in common with the lymphoproliferations which arise in the setting of transplantation. However, the patterns of latent EBV transcription in systemic HIV-related NHL is unique among NHL, suggesting that EBV may contribute differently to their pathogenesis.

Epstein-Barr virus (EBV) latent membrane protein (LMP) in tumor cells of Hodgkin's disease in pediatric patients

Twenty-nine out of 31 consecutive pediatric patients with Hodgkin's disease treated at our hospital from 1988 to 1992 were studied. The selection criterion was the availability of sufficient formalin-fixed, paraffin-embedded tissue for analysis. Patient age ranged from 3 to 15 years with a median age of 7 years. Lymph node biopsies were examined for the presence of Epstein-Barr virus (EBV)-encoded latent membrane protein (LMP) in malignant cells by peroxidase immunolabeling. LMP positivity was present in 10/15 (67%) of mixed cellularity, 1/6 (17%) of lymphocyte predominance, 0/7 (0%) of nodular sclerosis, and 1/1 (100%) of lymphocyte depletion. Positive cases by age range were: 10/12 (83%) for 3-6 years and 2/17 (11%) for 7-15 years. The association between EBV and Hodgkin's disease in children appeared to be more frequent in patients with mixed cellularity and those in the 3-6 age range, through examples of EBV-positive tumors were found in other histologic subtypes, stages and ages. Findings indicate that Hodgkin's disease in children is at least as strongly linked to EBV as in adults. Furthermore, we suggest that the EBV is associated with a subgroup of patients which can be defined on the basis of the age at diagnosis.

Differences in the growth pattern and clinical course of EBV-LMP1 expressing and non-expressing nasopharyngeal carcinomas

All low differentiated or anaplastic forms of nasopharyngeal carcinoma (NPC) carry multiple copies of EBV-DNA and express EBNA1. The major membrane protein, LMP1, is only expressed in 65% of the tumours. The physiological function of LMP1 in the viral life cycle is unknown, but it has been shown to transform established rodent fibroblasts and immortalised human keratinocytes in vitro, and to increase the likelihood of a malignant transformation. We studied 74 cases collected from the Shanghai and Guanzhou areas in China. LMP1 expression was assessed in tumour biopsies by immunoblotting. Clinical and follow-up data were evaluated according to the classification of WHO. The laboratory and the clinical data were assembled in a mutually independent double blind fashion. Our findings indicate that the LMP1-positive tumours grew faster and more expansively than LMP1-negative tumours, but nevertheless had a better prognosis. LMP1-negative tumours recurred at a higher frequency, and showed an increased tendency to metastasise.

Heterogeneity of Epstein-Barr virus infection in angioimmunoblastic lymphadenopathy type T-cell lymphoma

To investigate the relationship of Epstein-Barr virus (EBV) and angioimmunoblastic lymphadenopathy with dysproteinemia, we performed DNA analysis using the polymerase chain reaction (PCR), Southern blot, in situ hybridization, and immunohistochemical analysis of lymph nodes in five patients who were followed up and biopsied more than once. In the course of the disease, nodal architecture diminished, cellular atypia worsened, and clear cells increased in number. In the DNA analysis of the receptor genes, the clonal population increased in number. EBV nucleic acid sequences were found by either PCR or in situ hybridization in all examined nodes. The number of EBV-positive cells varied widely among the cases and throughout the course of the disease in the same patients. The analysis of EBV terminal repeats or lymphocyte-determined membrane antigen genes showed polyclonal populations of EB-infected cells. EBV-positive cells possessed intermediate- to large-sized nuclei, and the cells with large nuclei, especially, expressed latent membrane protein of EBV. These large cells varied among the cases. Double-labelling immunohistochemistry/in situ hybridization studies demonstrated that most of the EBV-positive cells expressed B-cell antigen (CD20). The presence of EBV seems to be associated with the selective defects of the immune system, rather than with the direct pathogenesis of angioimmunoblastic lymphadenopathy.

Frequent detection of Epstein-Barr virus (EBV), EBER transcripts and latent membrane protein-1 (LMP-1) in tumor cells in Hodgkin's disease arising in childhood

Paraffin sections from 22 cases of Hodgkin's disease (HD) and 30 cases of non-Hodgkin's lymphomas (NHL) occurring in childhood (3-15 years old) were examined for the presence of Epstein-Barr Virus (EBV) encoded EBER mRNAS and Latent Membrane Protein-1 (LMP-1) using RNA in situ hybridization (RISH) and immunohistochemistry, respectively. In 12/22 (54%) cases of HD the EBER transcripts were detected in most Reed-Sternberg and Hodgkin (HRS) cells as well as in some scattered smaller lymphoid cells. In all these cases the LMP-1 protein was detected exclusively in HRS cells. Three additional cases of HD were found to be EBER RISH positive only in a few scattered small lymphoid cells, the LMP-1 staining being negative in these cases. The EBER and LMP-1 positivity in HRS cells were present in 0/1 of lymphocyte predominant, 4/10 (40%) of nodular sclerosis and 8/11 (72%) of mixed cellularity of HD. No EBER RISH signal was found in tumor cells of the 30 cases of NHL. In four of them only a few scattered small lymphoid cells were EBER RISH positive. LMP-1 reactivity was not detected in any NHL. These results provide evidence for an association between EBV and a sizeable proportion of childhood Hodgkin's disease and show that this association is more frequent in mixed cellularity subtype. Furthermore, the detection of the LMP-1 protein in HRS cells in view of the LMP-1 transforming potential, suggests that EBV may be involved in the pathogenesis of a substantial proportion of cases of HD occurring in childhood.

Dual EBNA1 promoter usage by Epstein-Barr virus in human B-cell lines expressing unique intermediate cellular phenotypes

The use of different viral promoters for the expression of the EBNA1 gene product appears to be a critical step in the regulation of Epstein-Barr virus latent gene expression and may reflect the extent of differentiation of B-cell hosts. Low-passage Burkitt lymphoma cell lines resemble immature B cells in that they express CD10 (CALLA) and do not express B-cell activation antigens. In these cells, transcription from a promoter located in the BamHI F fragment of the viral genome results in the exclusive expression of EBNA1, referred to as the latency I pattern of viral gene expression. In contrast, high-passage Burkitt lymphoma cells and lymphoblastoid cell lines resemble activated B cells in that they do not express CD10 but do express activation antigens such as CD23. In these cells, the use of two promoters located in the BamHI W and C fragments of the viral genome leads to the expression of all six EBNA gene products (latency III). We have found that four human B-cell lines, DB, LBW2, LBW14, and Josh 7, stably express a pattern of B-cell differentiation antigens intermediate between those found in latency I and latency III cell lines and characterized by the coexpression of CD10 and CD23. The pattern of EBNA1 promoter usage in these cell lines was examined to determine whether their intermediate cellular phenotype was reflected in their patterns of viral gene expression. DB, LBW2, and LBW14 utilize both the BamHI F promoter region and BamHI W promoter region to transcribe the EBNA1 gene. This stable pattern of mixed promoter usage for the expression of the EBNA gene products in B cells has not previously been described. In addition, these three B-cell lines expressed lower levels of the viral latent gene product EBNA2 than those typically observed in latency III cells. The lower levels of activation of viral and cellular promoters known to be regulated by EBNA2 also correlated with the reduced levels of EBNA2 expression in these cells. These included the viral LMP1 and LMP2A promoters and the cellular CD23B promoter. The fourth B-cell line, Josh 7, expressed EBNA1 mRNAs derived from both the BamHI W promoter and BamHI C promoter, similar to latency III cells. The intermediate cellular phenotype in Josh 7 cells appeared to be due, in part, to a deficiency in the expression of viral LMP1.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of Ki67 antigen, epidermal growth factor receptor and Epstein-Barr virus-encoded latent membrane protein (LMP1) in nasopharyngeal carcinoma

The expression of Ki67 antigen, epidermal growth factor receptor (EGFR) and the Epstein-Barr virus (EBV)-encoded latent membrane protein (LMP1) in nasopharyngeal carcinoma (NPC) was immunohistochemically determined. In cases with sufficient material western blot analysis was applied to analyse the LMP1 expression. Biopsies from 20 Chinese and 3 Swedish patients with NPC were included in the study. Our results demonstrated a nuclear Ki67 staining, a membrane EGFR staining, and a dot-like cytoplasmic and/or membrane LMP1 staining pattern in tumour cells of NPC. The proportion of Ki67-positive cells correlated with tumour stage. A strong expression of EGFR was frequently seen in patients with tumour stages III and IV and was paralleled by a higher proportion of Ki67-positive cells. The majority of the LMP1-positive cases strongly expressed EGFR and had a higher proportion of Ki67-positive cells, indicating a possible effect of EBV LMP1 on the proliferation of tumour cells in NPC. The increased expression of EGFR and Ki67 in NPC at late tumour stage indicates their possible use in malignancy grading of NPC.

Upregulation of bcl-2 by the Epstein-Barr virus latent membrane protein LMP1: a B-cell-specific response that is delayed relative to NF-kappa B activation and to induction of cell surface markers

An ability of the Epstein-Barr virus latent membrane protein LMP1 to enhance the survival of infected B cells through upregulation of the bcl-2 oncogene was first suggested by experiments involving gene transfection and the selection of stable LMP1+ clones (S. Henderson, M. Rowe, C. Gregory, F. Wang, E. Kieff, and A. Rickinson, Cell 65:1107-1115, 1991). However, it was not possible to ascertain whether Bcl-2 upregulation was a specific consequence of LMP1 expression or an artifact of the selection procedure whereby rare Bcl-2+ cells already present in the starting population might best be able to tolerate the potentially toxic effects of LMP1. We therefore reexamined this issue by using two different experimental approaches that allowed LMP1-induced effects to be monitored immediately following expression of the viral protein and in the absence of selective pressures; activation of the NF-kappa B transcription factor and upregulation of the cell adhesion molecule ICAM-1 were used as early indices of LMP1 function. In the first approach, stable clones of two B-cell lines carrying an LMP1 gene under the control of an inducible metallothionein promoter were induced to express LMP1 in all cells. Activation of NK-kappa B and upregulation of ICAM-1 occurred within 24 h and were followed at 48 to 72 h by upregulation of Bcl-2. In the second approach, we tested the generality of this phenomenon by transiently expressing LMP1 from a strong constitutively active promoter in a range of different cell types. All six B-cell lines tested showed NF-kappa B activation in response to LMP1 expression, and this was followed in five of six lines by expression of ICAM-1 and Bcl-2. In the same experiments, all three non-B-cell lines showed NF-kappa B activation and ICAM-1 upregulation but never any effect upon Bcl-2. We therefore conclude that Bcl-2 upregulation is part of the panoply of cellular changes induced by LMP1 but that the effect is cell type specific. Our data also suggest that whilst NF-kappa B may be an essential component of LMP1 signal transduction, other cell-specific factors may be required to effect some functions of the viral protein.

Epstein-Barr virus recombinant molecular genetic analysis of the LMP1 amino-terminal cytoplasmic domain reveals a probable structural role, with no component essential for primary B-lymphocyte growth transformation

Previous recombinant Epstein-Barr virus molecular genetic experiments with specifically mutated LMP1 genes indicate that LMP1 is essential for primary B-lymphocyte growth transformation and that the amino-terminal cytoplasmic and first transmembrane domains are together an important mediator of transformation. EBV recombinants with specific deletions in the amino-terminal cytoplasmic domain have now been constructed and tested for the ability to growth transform primary B lymphocytes into lymphoblastoid cell lines. Surprisingly, deletion of DNA encoding EHDLER or GPPLSSS from the full LMP1 amino-terminal cytoplasmic domain (MEHDLERGPPGPRRPPRGPPLSSS) had no discernible effect on primary B-lymphocyte transformation. These two motifs distinguish the LMP1 amino-terminal cytoplasmic domain from other arginine-rich membrane proximal sequences that anchor hydrophobic transmembrane domains. Two deletions which included the ERGPPGPRRPPR motif adversely affected but did not prevent transformation. This arginine- and proline-rich sequence is probably important in anchoring the first transmembrane domain in the plasma membrane, since these mutated LMP1s had altered stability and cell membrane localization. The finding that overlapping deletions of the entire amino-terminal cytoplasmic domain do not ablate transformation is most consistent with a model postulating that the transmembrane and carboxyl-terminal cytoplasmic domains are the likely biochemical effectors of transformation.

bcl-2 proto-oncogene and Epstein-Barr virus latent membrane protein-1 expression in AIDS-related lymphoma

The expression of bcl-2 protein and Epstein-Barr virus (EBV) latent membrane protein 1 (LMP-1) was investigated in 18 cases of lymphoma occurring in the acquired immunodeficiency syndrome (AIDS). EBV small RNAs were detectable in tumour cells in all cases by in situ hybridization with EBER oligonucleotides. LMP-1 expression was detected in 61% of the cases, and 55% were positive for bcl-2. Dual expression of LMP-1 and bcl-2 was found in 8/18 (44%) cases, while five cases (28%) expressed either LMP-1 or bcl-2 and five expressed neither. Thus, there was an inconsistent relationship between the presence of EBV and the expression of bcl-2. One LMP-1 negative case was found to express bcl-2 in reactive lymphocytes but not in lymphoma cells. No clinical features were found to correlate statistically with LMP-1 or bcl-2 expression in the tumour cells. However, CD4 counts at diagnosis were significantly lower in bcl-2 positive cases (P < 0.05). The respective roles of EBV LMP-1 and the expression of bcl-2 in lymphogenesis in AIDS patients remains complex and is not yet fully understood.

Epstein-Barr virus (EBV)-related lymphoproliferative disorder with subsequent EBV-negative T-cell lymphoma

A 58-year-old Chinese man presented initially with generalized lymphadenopathy, and lymph-node biopsy showed disturbed architecture with preponderance of large B-blasts mixed with numerous CD8+ T lymphocytes, consistent with an acute Epstein-Barr virus (EBV) infection. Immunohistological and gene rearrangement studies confirmed the absence of clonal T or B cells. Polyclonal EBV with lytic infection was detected by Southern blot hybridization (SoBH). Expression of EBV proteins (EBNA2, LMP and ZEBRA) was detected in a proportion of cells by immunostaining. EBV-lytic proteins EA-D, VCA, MA were also detected in rare scattered cells. Double immunostaining showed that the LMP-positive cells were of B and of T phenotype: 73% CD19+, 26% CD2+, 23% CD3+, 8% CD4+, 17% CD8+. After biopsy, there was spontaneous regression of lymph-node enlargement, but lymphadenopathy recurred 8 months later, and the second lymph-node biopsy showed T-cell lymphoma, confirmed by detection of clonally rearranged T-cell-receptor beta-chain gene. However, EBV genome could not be detected in the second biopsy by SoBH, in situ hybridization for EBV-encoded EBER RNA, and immunostaining for EBNA2, LMP and ZEBRA was also negative. This case is of special interest because an EBV-negative T-cell lymphoma developed shortly after an acute episode of EBV-related lymphoproliferation, even though many EBV-positive T cells were detected during the acute episode. EBV was apparently not a direct cause of the lymphoma, but the close temporal association of the 2 lesions supports the hypothesis that EBV can act as a co-factor in lymphomagenesis.

Epstein-Barr virus and Hodgkin's disease: a comparative immunological, in situ hybridization, and polymerase chain reaction study

During recent years numerous studies have demonstrated the presence of Epstein-Barr virus (EBV) in tissues affected by Hodgkin's disease (HD). The percentage of cases with evidence of EBV infection has varied among the different studies, a positive result being highly dependent on the sensitivity of the method employed. In this study three different methods of detecting EBV in 48 cases of 'classical' HD (33 cases of nodular sclerosis and 15 cases of mixed cellularity) were compared: Immunohistochemistry (IH) for detection of latent membrane protein-1 (LMP-1), in situ hybridization (ISH) for detection of Epstein-Barr virus early RNAs (EBER 1 and 2), and polymerase chain reaction (PCR) for detection of a reiterated 110 base-pair EBV genomic sequence of the BamHI region. In 14 cases (29%) Hodgkin's (H) and Reed-Sternberg (RS) cells were positive for LMP-1 using IH, and in 21 cases (44%) positive signals were seen in H-RS cells with EBER 1 and 2 probes using ISH. A few EBER-positive non-malignant lymphocytes were seen in 17 cases. Thirty-two cases (71%) were EBV-positive by PCR. It is concluded that the PCR technique is the most sensitive method for detecting EBV in HD. However, this method cannot provide information about the cellular localization of EBV. ISH with EBER 1 and 2 probes is superior to immunohistochemical detection of LMP-1 with regard to sensitivity. The advantage that the latter two methods have over the PCR techniques is that it is possible to analyse whether the EBV infection occurs in the H-RS cells or in the admixed non-malignant cell population. Furthermore, this study supports the observation that EBV is associated with a considerable number of HD cases.

Epstein-Barr virus in nasal T-cell lymphomas (polymorphic reticulosis/midline malignant reticulosis) in western China

Polymorphic reticulosis (PR) or midline malignant reticulosis (MMR) is considered to be malignant, or at least pre-malignant T-cell proliferations of the nose or midline area. Recent reports of small series of nasal T-cell lymphomas have shown a strong association with Epstein-Barr virus (EBV). Furthermore, a peculiar phenotype is described, with expression of CD56 and not of CD3, suggesting a possible origin from natural killer (NK) cells. We have analysed a series of 38 cases of PR/MMR for the presence of EBV by in situ hybridization (ISH) of the EBV-encoded RNAs 1 and 2 (EBER). Twenty cases were tested for expression of EBV-encoded latent membrane protein 1 (LMP-1). Special attention was also paid to the expression of CD3 and the NK cell-related marker CD56. Thirty-two cases (84 per cent) showed positive EBER ISH. In 5 of 20 cases, LMP-1 expression was detected. In three cases, a few scattered cells were positive, and in two cases, LMP-1 was detected in clusters of atypical cells. Most of the neoplasms showed expression of CD3 (89 per cent) and in 27 cases (71 per cent), CD56 was detected. These results are consistent with an aetiopathogenetic role for EBV in most, but not all, cases of PR/MMR. Our findings are less supportive of a major role for LMP-1 in tumour genesis. CD3 expression in most of the cases of PR/MMR underlines the T-cell origin of these neoplasms, often with aberrant expression of CD56.

Epstein-Barr virus nuclear antigen EBNA3C/6 expression maintains the level of latent membrane protein 1 in G1-arrested cells

The Epstein-Barr virus in the Burkitt lymphoma-derived cell line Raji has a deletion in the EBNA3C gene. When Raji cells are allowed to grow to high density and most of the cells become growth arrested in the G1 phase of the cell cycle, the level of detectable latent membrane protein 1 (LMP1) is substantially reduced. After dilution of the cells with fresh growth medium, within 8 h, there is a large increase in LMP1 mRNA, and by 12 h, LMP1 is expressed to a high level (H. Boos, M. Stoehr, M. Sauter, and N. Mueller-Lantzch, J. Gen. Virol. 71:1811-1815, 1990). Here we show that in Raji cells which constitutively express a transfected EBNA3C gene, the down-regulation of LMP1 in growth-arrested cells does not take place. Furthermore, we show that in wild-type Raji cells, low-level LMP1 expression occurs when most of the cells are arrested at a point(s) early in G1 (or G0) when the product of the retinoblastoma gene, pRb, is hypophosphorylated. The dramatic synthesis of LMP1 coincides with the progression of these cells to late G1 when pRb becomes hyperphosphorylated. Thus, in Raji cells, the LMP1 gene is apparently regulated in a cell cycle- or proliferation-dependent manner, but when EBNA3C is present, sustained LMP1 expression occurs as it does in a lymphoblastoid cell line. EBNA3C appears to either relieve the apparent repression of LMP1 in cells progressing through early G1 or possibly alter the stage at which the cells growth arrest to one where they are permissive for LMP1 expression.

Effect of beta-lymphocyte- and NPC-derived EBV-LMP1 gene expression on in vitro growth and differentiation of human epithelial cells

The effect of expression of the Epstein-Barr-virus (EBV) latent membrane protein (LMP1) derived from B-lymphocytes (B) and nasopharyngeal carcinoma (NPC) (C) on the in vitro growth and differentiation of a human keratinocyte line, Rhek-1, was analyzed in clonal growth and in in vitro differentiation assays. In contrast to the polygonal parental cells, the B-LMP1-expressing sublines were spindle-shaped while the C-LMP1-expressing cells were pleomorphic. Both B- and C-LMP1-expressing sublines showed increased proliferation as evidenced by: (1) higher colony-forming efficiency (CFE) and larger colony size at reduced serum levels; (2) an increased number of epithelial cell layers formed in the air-liquid-interface culture system and (3) increased expression of proliferative cell nuclear antigen (PCNA). At low serum concentration, the C-LMP1-expressing sublines formed larger colonies than those expressing B-LMP1. In the air-liquid-interface culture system, both B- and C-LMP1-expressing lines showed reduced epithelial differentiation resulting in reduced stratification and reduced involucrin expression similar to those of the cancer cell line, Siha. The results of the present study indicate that the expression of LMP1 in human keratinocytes is associated with morphological transformation and predisposes these cells to a more neoplastic phenotype. The structural difference between the 2 genes responsible for the functional differences and transforming ability will be pinpointed in further experiments.

A Ca2+/calmodulin-dependent protein kinase, CaM kinase-Gr, expressed after transformation of primary human B lymphocytes by Epstein-Barr virus (EBV) is induced by the EBV oncogene LMP1

CaM kinase-Gr is a multifunctional Ca2+/calmodulin-dependent protein kinase which is enriched in neurons and T lymphocytes. The kinase is absent from primary human B lymphocytes but is expressed in Epstein-Barr virus (EBV)-transformed B-lymphoblastoid cell lines, suggesting that expression of the kinase can be upregulated by an EBV gene product(s). We investigated the basis of CaM kinase-Gr expression in EBV-transformed cells and the mechanisms that regulate its activity therein by using an EBV-negative Burkitt lymphoma cell line, BJAB, and BJAB cells converted to expression of individual EBV proteins by single-gene transfer. CaM kinase-Gr expression was upregulated in BJAB cells by EBV latent-infection membrane protein 1 (LMP1) but not by LMP2A or by nuclear proteins EBNA1, EBNA2, EBNA3A, and EBNA3C. In LMP1-converted BJAB cells, the kinase was functional and was dramatically activated upon cross-linking of surface immunoglobulin M. Overlapping cDNA clones that encode human CaM kinase-Gr were sequenced, revealing 81% amino acid identity between the rat and human proteins. Transfection of BJAB cells with an expression construct for the human enzyme resulted in a functional kinase which was shown by epitope tagging to localize primarily to cytoplasmic and perinuclear structures. Induction of CaM kinase-Gr expression by LMP1 provides the first example of a Ca2+/calmodulin-dependent protein kinase upregulated by a viral protein. In view of the key role played by LMP1 in B-lymphocyte immortalization by EBV, these findings implicate CaM kinase-Gr as a potential mediator of B-lymphocyte growth transformation.

Detection of Epstein-Barr virus DNA in Hodgkin- and Reed-Sternberg-cells by single cell PCR

The Epstein-Barr virus (EBV) can be detected in the majority of lymph nodes involved by Hodgkin's lymphoma using the highly sensitive polymerase chain reaction (PCR). However, the rate of EBV-DNA detection by in-situ hybridisation, which allows allocation of EBV to a defined cell population, i.e. the neoplastic H&RS-cells, is lower. In an attempt to combine the advantages of the high sensitivity of the PCR and the possibility of cellular allocation by in-situ hybridisation, we established a single-cell PCR of Hodgkin- and Reed-Sternberg (H&RS)-cells isolated by micromanipulation from biopsy tissues. We amplified EBV sequences from the BamW-region by single-cell PCR. Using this method we were able to detect EBV-DNA in the H&RS-cells from 4 of 6 patients. In EBV positive cases all H&RS-cells of a given patient were positive, proving the high sensitivity and reproducibility of the method. Other cells in the biopsy tissue involved by EBV-positive H&RS-cells were shown to be negative. This indicates that EBV may have a role in the pathogenesis of many but not all cases of Hodgkin's disease.

Interferon alpha and intracytoplasmic free calcium in hairy cell leukemia cells

Hairy cell leukemia (HCL) is a B-cell tumor affecting the pre-plasma stage of B cell differentiation. One of the most striking characteristics of this disease is its remarkable responsiveness to alpha-interferon (IFN-alpha) therapy. Interferons constitute a heterologous family of multifunctional cytokines displaying anti-viral, anti-proliferative and immunoregulatory properties. These activities have been extensively studied in hairy cells, but the mechanism of action of IFN-alpha in hairy cell leukemia remains unknown. Our approach to investigate the mode action of IFN-alpha in HCL has been to identify abnormalities which occur in these tumor cells and then to ascertain whether these abnormalities can be rectified by IFN-alpha treatment. A high level of free Ca2+ in the cytoplasm of hairy cells was identified. Increases in cytosolic Ca2+ are believed to be a pivotal signal in regulating cell proliferation, cell differentiation and cell death. These high Ca2+ levels in hairy cells could be reduced upon treatment with IFN-alpha either in vitro or in vivo, probably acting by reducing Ca2+ influx into the leukemic cells. Moreover, the effect of IFN-alpha on [Ca2+]i seems to be correlated with down-regulation of CD20 phosphorylation, a B cell specific phosphoprotein involved in Ca2+ influx across the plasma membrane. The possible origins and implications of Ca2+ deregulation and the possible mechanisms or sites of action of IFN-alpha in tumor cells from HCL are explored in this review.

The impact of EBV, proliferation rate, and Bcl-2 expression in Hodgkin's disease in childhood

The role of Epstein-Barr virus (EBV) in the pathogenesis of Hodgkin's disease (HD) has not yet been clarified. Using RNA in situ hybridization (ISH) and immunohistochemistry (IHC), the occurrence of small Epstein-Barr virus encoded RNA (EBER) and latent membrane protein-1 (LMP-1) was studied in 22 tissue samples from 21 patients between 4 and 17 years of age with Hodgkin's disease. EBER was detected in eight of 21 patients (38%) in Hodgkin and Reed-Sternberg cells and reactive lymphocytes irrespective of initial clinical stage and histological subtype, whereas LMP-1, positive in ten of 21 patients (48%), was restricted to neoplastic cells. All cases positive for EBER expressed LMP-1 as well. Additionally, oncoprotein Bcl-2 was identified in nine of 21 patients (43%), indicating, besides immortalization of HD cells by EBV, a further growth advantage due to apoptosis prevention by overexpression of this protein. Proliferation-associated antigens Ki-S1 and Ki-S5 were highly expressed in Hodgkin and Reed-Sternberg cells. CD 30 antigen was found in most cases, using two different antibodies (90% and 80%). The presence of this protein, which belongs to the family of nerve growth factor receptor (NGFR), is related to high expression of Ki-67 protein, detected by Ki-S5. CD 20 antigen was detectable in only three of 21 patients (14%). If we compare results of ISH and IHC with clinical data, the occurrence of EBV genome in children with HD seems to have no adverse effect on the final outcome of these patients.

BCL-2 induction is part of the strategy of Epstein-Barr virus

Epstein Barr virus can infect B lymphocytes and epithelial cells. Epithelial cells present the natural reservoir for the virus in man. In vitro, infected cells harbor the virus predominantly in a latent state with the expression of a set of nuclear (EBNA 1-6) and latent membrane genes (LMP 1-2) and virus-transformed B cells grow as permanently immortalized lymphoblastoid cell lines, that show increased resistance to various growth inhibiting factors. Here we show that the lymphoma-associated oncogene BCL-2 is upregulated by different latent Epstein-Barr virus genes in B lymphocytes as well as keratinocyte cell lines. Thus, the induction of BCL-2 gene expression seems to be part of the survival strategy of the virus independently of the host cell infected.

An integral membrane protein (LMP2) blocks reactivation of Epstein-Barr virus from latency following surface immunoglobulin crosslinking

The role of latent membrane protein 2 (LMP2) in Epstein-Barr virus (EBV) infection was evaluated by using latently infected primary B lymphocytes that had been growth transformed by wild-type or specifically mutated EBV recombinants. LMP2 null mutant recombinant EBV-infected cells were similar to normal B lymphocytes in their rapid increase in intracellular free calcium after surface immunoglobulin crosslinking. These cells also became more permissive for lytic EBV replication. In sharp contrast, wild-type control infected cells had little or no increase in intracellular free calcium or in permissivity for EBV replication. The block to surface immunoglobulin crosslinking-induced permissivity in cells expressing wild-type LMP2 could be bypassed by raising intracellular free calcium levels with an ionophore and by activating protein kinase C with phorbol 12-myristate 13-acetate. LMP2A, not LMP2B, mediates this effect on calcium mobilization. Genetic and biochemical data are consistent with these effects being due to the interaction of the LMP2A N-terminal cytoplasmic domain with B lymphocyte src family tyrosine kinases.

Prevalence of Taiwan variant of Epstein-Barr virus in throat washings from patients with head and neck tumors in Taiwan

The prevalence of the Epstein-Barr virus (EBV) Taiwan variant was investigated in the throat washing (TW) samples from patients with head and neck tumors, persons with nonmalignant diseases, and healthy adults in Taiwan. By using the EBV (BNLF-1 gene)-specific primers and PCR, the EBV latent membrane protein gene BNLF-1 was detected in 91 (61%) of the 150 TW samples from patients with tumors, including 25 (78%) of 32 patients with nasopharyngeal carcinoma and 66 (56%) of 118 other patients with head and neck tumors. The TW samples from the 26 patients with nonmalignant tumors and 53 healthy adults were also examined. Approximately 47% of these samples were positive for the EBV gene. The PCR products of the BNLF-1 gene were then subjected to XhoI digestion. Sixty-eight of 91 PCR products (75%) showed the loss of the XhoI site, which indicated the presence of a Taiwan strain of EBV in patients with tumors. The DNA sequence of the BNLF-1 gene of the Taiwan variant revealed that the loss of the XhoI site was due to a nucleotide change from a G to a T at position 169,426 in comparison with the sequence of prototype EBV B95-8 cells. Furthermore, the Taiwan strain appeared significantly more frequently in the TWs and tissue samples from patients with nasopharyngeal carcinoma (88%; P < 0.001) and laryngeal carcinoma (80%; P < 0.02) than in those samples from healthy adults (about 40%). These data indicate that a Taiwan variant of EBV may be closely associated with head and neck tumors and suggest that this variant may be important in the pathogenesis of head and neck tumors.

Lymphoma complicating immunodeficiency disorders

BACKGROUND

An increased incidence of lymphoma is seen in various types of immune deficiency or dysregulation, including congenital immune deficiency diseases, organ transplantation with iatrogenic immunosuppression, autoimmune disorders, endemic Burkitt's lymphoma, and AIDS-associated lymphoma.

RESULTS

The lymphomas seen in various immunodeficiency disorders share certain features. Thus, all consist of high-grade, B-cell tumors, with predilection for extranodal involvement, and short survival. However, certain biologic and clinical differences are also apparent. Thus, while the transplantation-associated lymphomas are uniformly associated with the Epstein-Barr Virus (EBV), this association is not seen in all systemic AIDS-related lymphomas, nor in all congenital immune deficiency disorders. Likewise, while c-myc activation has been described in certain types of HIV-related lymphomas, c-myc dysregulation has not been reported in association with organ transplantation.

CONCLUSIONS

The study of lymphomatous disease in various states of immune dysregulation may allow an understanding of the diverse pathogenic mechanisms operative in the development of malignant lymphoma in man.

Is Hodgkin's disease an infectious disease?

Several lines of evidence question the concept of Hodgkin's disease (HD) starting as a true malignant disorder of the lymphatic system: (i) In early stages HD exerts pronounced clinical and biological features of an atypic immune response. (ii) Despite extensive investigations, the Hodgkin/Reed-Sternberg (H/RS) cells have not been unequivocally determined as the definite malignant cell population in HD. (iii) The epidemiological pattern of HD strongly resembles that of an infectious disease. (iv) About 50% of HD cases can be linked to infection with Epstein-Barr virus. Hodgkin's disease in early stages might thus be understood as the unsuccessful attempt of the organism to eliminate a cell expressing a putative (cellular or viral) target antigen. A stepwise transformation of this antigen-carrying cell, possibly triggered by an inherent genetic instability, might then lead to outgrowth of a malignant cell clone in late stages of the disease.

Encoded latent membrane protein 1 of Epstein-Barr virus on follicular dendritic cells in residual germinal centres in Hodgkin's disease

AIMS

To determine if there is an association between Epstein-Barr virus (EBV) infection and Hodgkin's disease.

METHODS

Fifty cases of Hodgkin's disease and 25 reactive lymph nodes were screened for the presence of EBV-RNA (EBER) using in situ hybridisation, and for the expression of EBV encoded latent membrane protein 1 (LMP-1) by immunohistochemistry.

RESULTS

In 42% of the cases of Hodgkin's disease, EBER was detected in the nuclei of the malignant cells, and in LMP-1 expression was found 36%. Both EBER and LMP-1 positivity were seen in 34% of the cases. An additional finding was the presence of LMP-1 on follicular dendritic cells in residual germinal centres in two cases of Hodgkin's disease. EBER was not detected in these germinal centres. In reactive lymph nodes only occasional EBER positive, small, lymphoid cells were found, without LMP-1 expression.

CONCLUSIONS

These results show a strong correlation between the presence of EBER and the LMP-1 expression in the Reed-Sternberg cells. They corroborate a role for EBV in at least some cases of Hodgkin's disease. LMP-1 is probably presented as an immune complex in the germinal centres, as part of an immune response against EBV.

Epstein-Barr virus and carcinomas

The Epstein-Barr virus, a human B lymphotropic herpes virus, is strongly associated with undifferentiated nasopharyngeal carcinoma, which is endemic in Southern China and North Africa. More recently, an association of the virus with certain other epithelial malignancies has been described, some of which are more common in Western countries. Also, the observation that oral hairy leukoplakia, an acquired immunodeficiency syndrome-related lesion of the tongue, supports Epstein-Barr virus replication in the epithelial cell compartment has further strengthened the notion that Epstein-Barr virus infection of epithelial cells may be an important phenomenon in vivo. The purpose of this article is to review the association of Epstein-Barr virus with nasopharyngeal carcinomas, to examine the evidence suggesting an association of the virus with other epithelial neoplasias and to discuss Epstein-Barr virus infection of non-neoplastic epithelial cells.

Mutants of Epstein-Barr virus with a selective marker disrupting the TP gene transform B cells and replicate normally in culture

We have isolated mutants of Epstein-Barr virus (EBV) which carry a dominant selectable marker inserted into the third exon of the gene encoding two membrane proteins, TP1 and TP2 (or LMP2A and LMP2B), which are expressed in latently infected, growth-transformed B cells. One of the mutants also acquired a 260-bp deletion beginning in the first intron a few base pairs from the terminal repeats and removing most of the second TP exon, including the initial coding sequences of TP2. These EBV mutants transform human B cells in culture, and the transformed B-cell clones carrying them release EBV at approximately normal frequencies.

Epstein-Barr virus subtype distribution in angioimmunoblastic lymphadenopathy

The tissues of 16 patients bearing a T-cell lymphoma of angioimmunoblastic lymphadenopathy type (AILD-TCL) were investigated for the distribution of Epstein-Barr virus (EBV) subtypes 1 and 2. EBV-association had been proven in these cases by polymerase chain reaction (PCR) for EBV-DNA, in situ hybridization (ISH) for EBV-encoded small nuclear RNAs (EBER) and immunohistology for EBV-encoded latent membrane protein (LMP). PCR and EBER-ISH produced mostly identical results, but some cases were positive with only one of the 2 methods employed. LMP was detected in a few large cells of 8/13 cases. Twelve cases were investigated for the distribution of EBV subtypes. One case contained EBV genome of subtype 2, 3 cases contained subtype 1 and 4 cases contained both subtypes. Four cases could not be typed. These findings suggest that in AILD, as in AIDS-associated lymphomas and lymphomas of the lethal midline granuloma type, subtype 2 of EBV may occur, perhaps in relation to an immunodysfunction developing progressively in these patients.

Marked, transient inhibition of expression of the Epstein-Barr virus latent membrane protein gene in Burkitt's lymphoma cell lines by electroporation

The Raji, EB1, and EB2 cell lines are derived from Epstein-Barr virus (EBV)-positive Burkitt's lymphomas. EBV gene products associated with viral latency, including latent membrane protein (LMP) and Epstein-Barr nuclear antigen 2 (EBNA-2), are expressed in these cell lines. We have found that transfection of all three of these cell lines by electroporation in both the presence and the absence of foreign DNA resulted in a marked decrease in expression of the endogenous EBV gene encoding LMP. An analysis of this response in Raji cells revealed that the level of RNA of this gene was decreased transiently and returned to normal levels by 7 days after transfection. The level of LMP protein was also reduced after transfection. No difference in survival was detected in electroporated versus unperturbed Raji cells. The level of mRNA encoding a modulator of the LMP gene, EBNA-2, was unchanged by electroporation. However, the level of another EBV transcript, BHLF-I, was reduced. The effect of electroporation could not be attributed to flux of Ca2+, Na+, K+, or Cl- ions across the plasma membrane. Expression of LMP in several lymphoblastoid cell lines was unaffected by electroporation.

Epstein-Barr virus latent membrane protein 1 is essential for B-lymphocyte growth transformation

The gene encoding latent-infection membrane protein 1 (LMP1) was specifically mutated in Epstein-Barr virus (EBV) recombinants by inserting a nonsense linker after codon 9 or codon 84 or into an intron 186 bp 3' to the latter insertion site. EBV recombinants with the LMP1 intron mutation were wild type for LMP1 expression and for growth transformation of primary B lymphocytes. In contrast, EBV recombinants with the mutations in the LMP1 open reading frame expressed N-terminally truncated crossreactive proteins and could initiate or maintain primary B-lymphocyte transformation only when wild-type LMP1 was provided in trans by a coinfecting, transformation-defective EBV, P3HR-1. These data indicate that LMP1 is essential for EBV-mediated transformation of primary B lymphocytes, that the first 43 amino acids are critical for LMP1's function, and that codon 44-initiated LMP1 does not have a dominant negative effect on transformation.

Viral immunopathology of human tumors

Virally induced tumors provide the strongest case of host surveillance against neoplastic cells and their precursors. Human cancers associated with Epstein-Barr virus, hepatitis B virus, papilloma virus and human T cell leukemia virus infection are responsible for approximately 15-20% of the total incidence of cancer world-wide. Current work in each of these virus/tumor systems seeks to understand the mechanisms of viral action and to identify strategies of immune intervention that may allow us to prevent viral infection or to control its potentially life-threatening consequences.

The association between Epstein-Barr virus and Chinese Hodgkin's disease

Epstein-Barr virus (EBV) can be detected in Hodgkin and Reed-Sternberg (HRS) cells in about one-half of cases of Hodgkin's disease (HD) in Western countries. To determine whether EBV is also associated with HD in a developing country such as China, we studied paraffin sections from 28 Chinese cases of HD for expression of latent membrane protein-I (LMP-I) and EBV-encoded small RNA (EBER-I), using immuno-histology and RNA/RNA in situ hybridization respectively. The cases were selected from a large series of Chinese lymphomas following histological and immunophenotypical revision. EBV gene expression was found in HRS cells in 17/28 cases, and was related to histological sub-type, being present in 10/11 of mixed cellularity, 6/14 nodular sclerosis, 0/1 lymphocytic predominance, 0/1 lymphocytic depletion, and 1/1 unclassified HD. The 2 methods for detecting EBV gene expression gave similar results, except in one case of nodular sclerosis, in which HRS cells were negative for EBER-I, but weakly positive for LMP-I. In 5/12 cases with EBER-negative HRS cells, rare small or medium-sized lymphocytes expressed EBER-I but not LMP-I. These results suggest that (i) Chinese HD is frequently associated with EBV; (ii) the proportional frequency and sub-type distribution of EBV-positive HD are similar in China and in the West; (iii) both LMP-I immunohistology and EBER in situ hybridization reliably detect EBV in HRS cells in routine biopsies, but the former is simpler and less resource-consuming to perform.

Latent membrane protein of Epstein-Barr virus induces cellular phenotypes independently of expression of Bcl-2

The stable expression of the Epstein-Barr virus (EBV) latent membrane protein (LMP) in certain EBV-negative Burkitt's lymphoma cell lines correlates with an increased expression of the oncogene Bcl-2 (S. Henderson, M. Rowe, C. Gregory, D. Croom-Carter, F. Wang, R. Longnecker, E. Kieff, and A. Rickinson, Cell 65:1107-1115, 1991). This finding is consistent with a model in which Bcl-2 contributes to the immortalization of B cells mediated by EBV. We therefore asked whether the expression of Bcl-2 protein correlates with the induction of three cellular phenotypes induced by or associated with LMP. The expression of Bcl-2 in primary B cells infected with the B95-8 strain of EBV varied between 1 and 1.8 times that in uninfected cells when 50% of the cells were infected, expressed LMP, and incorporated 20-fold more [3H]thymidine than did uninfected cells. This finding indicates that induced proliferation of these primary cells is not sufficient to induce Bcl-2. We found that BALB/c 3T3 cells and their derivatives transformed by LMP do not express Bcl-2 detectably. The expression of LMP at high levels in lymphoid cells is cytotoxic and correlates with an increased expression of Bcl-2 following stable selection for the introduced LMP gene; 2 days after transfection, control vector- and LMP-transfected populations, however, express equal levels of Bcl-2 protein. We also analyzed transient expression of LMP in an EBV-negative Burkitt's lymphoma cell line. Infection of BJAB cells with the B95-8 strain of EBV results in an increase in Bcl-2 expression with a time course similar to that of LMP expression, and LMP alone transiently induces an increase in Bcl-2 expression in these cells. We interpret these observations to indicate that increased expression of Bcl-2 is unlikely to contribute to the ability of EBV to immortalize primary B cells and that both the transformation of rodent cells and the cytotoxicity mediated by LMP are independent of Bcl-2.

Characteristic clinicopathologic features of Epstein-Barr virus-associated peripheral T-cell lymphoma

BACKGROUND

The authors previously reported the existence of a unique subtype of peripheral T-cell lymphoma (PTCL) characterized by a clonotypical proliferation of Epstein-Barr virus (EBV) in the tumor cells (Blood 1991; 77:799). Detailed clinicopathologic features of this newly recognized entity remain to be clarified.

METHODS

A retrospective study was done in 23 patients receiving consecutive diagnoses at National Taiwan University Hospital by methods previously described.

RESULTS

There were 13 male and 10 female patients, with a median age of 40 years. Seventeen patients had Stage III/IV disease, and 15 patients had fever as a presenting B symptom. Initial extranodal involvement occurred in skin (10 patients), lung (4 patients), bone marrow (4 patients), brain (3 patients), and nasal cavity (1 patient) and was evidenced by hepatosplenomegaly (6 patients). Sixteen patients had specific histopathologic features including characteristics similar to angioimmunoblastic lymphadenopathy with dysproteinemia (3 patients), angioinvasive-type features (6 patients), Hodgkin disease-like features (2 patients), hepatosinusoidal-type features (2 patients), Lennert lymphoma (2 patients), and malignant histiocytosis-like features (1 patient). Six (37.5%) of the 16 patients who received a standard regimen with cyclophosphamide, doxorubicin, vincristine, and prednisone or an equivalent regimen as induction chemotherapy achieved complete remission. The median survival time was only 8 months. Six (42.8%) of the 14 patients who have died at this report ended up with a terminal hemophagocytosis syndrome. All five relapsed tumors were found to have a strong expression of P-glycoprotein (P-gp).

CONCLUSIONS

The authors suggest that EBV-associated PTCL should be regarded as a separate entity of non-Hodgkin lymphoma showing characteristic histopathologic features, frequent expression of P-gp in relapsed tumor, a terminal hemophagocytosis syndrome, and a generally ominous outcome.

Deletion of DNA encoding the first five transmembrane domains of Epstein-Barr virus latent membrane proteins 2A and 2B

A recombinant Epstein-Barr virus (EBV) was constructed, with a positive-selection marker inserted at the site of a deletion of a DNA segment which encodes the first five transmembrane domains of LMP2A and LMP2B. Despite the mutation, the mutant recombinant EBV was able to initiate and maintain primary B-lymphocyte growth transformation in vitro. Cells transformed with the mutant recombinant were not different from wild-type virus transformants in initial or long-term outgrowth, sensitivity to limiting cell dilution, or serum requirement. Expression of EBNA1, EBNA2, EBNA3A, EBNA3C, and LMP1 and permissivity for lytic EBV infection were also unaffected by the LMP2 deletion mutation. These results complete the molecular genetic studies proving LMP2 is dispensable for primary B-lymphocyte growth transformation, latent infection, and lytic virus replication in vitro.

Expression of Epstein-Barr virus latent gene products and related cellular activation and adhesion molecules in Hodgkin's disease and non-Hodgkin's lymphomas arising in patients without overt pre-existing immunodeficiency

Epstein-Barr virus (EBV) recently has been associated with Hodgkin's disease (HD) and the EBV genome was found in CD30-positive Reed-Sternberg cells. Therefore, tissue sections from 25 cases of HD, 35 cases of CD30-positive non-Hodgkin's lymphoma (NHL) (seven CD30-positive anaplastic large cell lymphomas [ALCLs] and 28 CD30-positive non-ALCLs), and 12 cases of CD30-negative NHL that previously had been screened for the presence of EBV by polymerase chain reaction and DNA in situ hybridization were studied by immunohistochemistry for the expression of the latent EBV proteins, latent membrane protein (LMP), and Epstein-Barr nuclear antigen-2 (EBNA-2). We also analyzed the expression of the B-cell activation molecule CD23 and the adhesion molecules LFA-1/CD11a and ICAM-1/CD54 because the upregulation of these molecules by LMP and/or EBNA-2 in vitro has been related to the EBV-induced lymphocyte growth. Latent membrane protein expression was found in Reed-Sternberg cells in nine of 25 cases (36%) of HD and in large, occasionally Reed-Sternberg-like tumor cells in six of 47 cases (12%) of NHL; these six tumors were CD30-positive, histologically high-grade NHL (one CD30-positive ALCL and five CD30-positive non-ALCLs). All the LMP-positive cases were also polymerase chain reaction EBV positive while LMP expression was not found in polymerase chain reaction EBV-negative HD and NHL. No staining for EBNA-2 was detected in our series. In view of the transforming potential of the LMP, these findings suggest that EBV may be associated with the development of some cases of HD and CD30-positive NHL. These findings also suggest a correlation between the expression of LMP and the detection of CD30 in tumor cells of HD and NHL. In contrast, no correlation was found between the expression of LMP and the detection of CD23, LFA-1/CD11a, and ICAM-1/CD54 in tumor cells of HD and NHL.

Complex nature of the major viral polyadenylated transcripts in Epstein-Barr virus-associated tumors

The most abundant polyadenylated viral transcripts in the Epstein-Barr virus (EBV)-associated tumor nasopharyngeal carcinoma are a family (apparent sizes, 4.8, 5.2, 6.2, and 7.0 kb) of highly spliced cytoplasmic RNAs expressed from the BamHI-I and -A regions of the viral genome in an antisense direction with respect to several viral lytic functions encoded within the same region and concerned with the lytic cycle of the virus. We have called these complementary-strand transcripts. They are also expressed in B cells, including Burkitt's lymphoma and EBV-immortalized marmoset cell lines, and tumors generated in cottontop tamarins in response to EBV infection, but at a lower level. The complete structure of the major 4.8-kb RNAs (seven or eight exons) was determined in this study; the larger, but related, transcripts appear to be produced by differential splicing. The transcriptional promoter for the major complementary-strand transcripts, located in BamHI-I, contains several well-characterized transcriptional control elements (E2A, SP1, and AP1) and is functionally active in both B lymphocytes and epithelial cells. It appears to be a bifunctional viral promoter, as it also contains the initiation codon for a gene (BILF2) that encodes a glycoprotein that is expressed off the other strand. Splicing events create a number of small AUG-initiated open reading frames, one of which has homology to functionally significant regions of the EBV-encoded nuclear antigen 2 and to E2 (in papillomavirus). The complex nature of these transcripts and their potential role in the virus association with malignancy are considered.

Epstein-Barr virus (EBV) in enteropathy-associated T-cell lymphoma (EATL)

Using Southern hybridization analysis, we have detected the Epstein-Barr virus (EBV) genome in 36 per cent (4/11) of enteropathy-associated T-cell lymphoma (EATL), a frequency much higher than that seen in nodal T-cell lymphomas in which we were able to show EBV DNA in only 3 per cent (1/30) of the cases examined. Using a terminal fragment probe, monoclonal proliferation of EBV in infected cells was demonstrated in three of the four EBV-positive EATL cases (in one case, insufficient signal prevented the determination of EBV clonality). The EBV genome and an early transcript, EBER1, were identified in tumour cells by in situ hybridization. Expression of latent membrane protein (LMP) was detected in two EBV DNA/RNA-positive EATL cases. In view of the known oncogenic properties of EBV and the putative central role of LMP in EBV-induced cell immortalization, the results of this study suggest that the virus may play an aetiological role in the pathogenesis of EATL.

Epstein-Barr virus latent membrane protein 2A blocks calcium mobilization in B lymphocytes

LMP2A is expressed in latent Epstein-Barr virus (EBV) infection and interacts with LMP1 and members of the src tyrosine kinase family in the plasma membrane. Since tyrosine kinase mediate receptor-induced changes in intracellular free calcium, the effect of LMP2A on receptor-mediated intracellular calcium mobilization was evaluated by stably expressing LMP2A in an EBV-negative Burkitt tumor cell line (BJAB) or in LMP1-converted BJAB cells. LMP2A significantly blocked calcium mobilization following class II, CD19, or immunoglobulin M cross-linking. LMP2A effects were partially reversed in LMP1-converted cell lines. These results are compatible with LMP2A acting in latent B-lymphocyte infection to downmodulate LMP1 effects on cell growth or to inhibit induction of lytic EBV infection in specific human tissues following receptor ligation.

Epstein-Barr virus-related lymphomagenesis in a child with Wiskott-Aldrich syndrome

Epstein-Barr virus (EBV) DNA was detected in immunoblastic lymphoma arising in a child with the primary immunodeficiency, Wiskott-Aldrich syndrome. Southern blot analysis of the structure of the EBV genome revealed that the lymphoma was monoclonal and contained episomal EBV DNA. The EBV latent genes, latent membrane protein 1 (LMP1) and the EBV nuclear antigen 2 (EBNA2), were detected by immunohistochemistry in the Wiskott-Aldrich lymphoma but not in an EBV-positive Burkitt's lymphoma, implying that host immune factors could influence EBV gene expression. Hybridization in situ demonstrated expression of EBV-encoded RNA (EBER), the cellular c-fgr protooncogene, and CD23 B-cell activation transcripts in the Wiskott-Aldrich lymphoma whereas EBER and c-fgr but not CD23 were expressed in the Burkitt's lymphoma. These data suggest that in primary immunodeficiency-related lymphoma, LMP1 and EBNA2 are expressed and that this expression correlates with expression of CD23. This supports previous in vitro studies showing that CD23 is specifically induced by LMP1 or EBNA2 genes. In contrast, expression of c-fgr may be independent of expression of these EBV latent genes.