Epstein-Barr virus markers in a series of Burkitt's lymphomas from the West Nile District, Uganda

Worldwide Prevalence of Epstein-Barr Virus in Patients with Burkitt Lymphoma: A Systematic Review and Meta-Analysis

Burkitt lymphoma (BL) is a form of B-cell malignancy that progresses aggressively and is most often seen in children. While Epstein-Barr virus (EBV) is a double-stranded DNA virus that has been linked to a variety of cancers, it can transform B lymphocytes into immortalized cells, as shown in BL. Therefore, the estimated prevalence of EBV in a population may assist in the prediction of whether this population has a high risk of increased BL cases. This systematic review and meta-analysis aimed to estimate the prevalence of Epstein-Barr virus in patients with Burkitt lymphoma. Using the appropriate keywords, four electronic databases were searched. The quality of the included studies was assessed using the Joanna Briggs Institute's critical appraisal tool. The results were reported as percentages with a 95% confidence interval using a random-effects model (CI). PROSPERO was used to register the protocol (CRD42022372293), and 135 studies were included. The prevalence of Epstein-Barr virus in patients with Burkitt lymphoma was 57.5% (95% CI: 51.5 to 63.4, n = 4837). The sensitivity analyses demonstrated consistent results, and 65.2% of studies were of high quality. Egger's test revealed that there was a significant publication bias. EBV was found in a significantly high proportion of BL patients (more than 50% of BL patients). This study recommends EBV testing as an alternative for predictions and the assessment of the clinical disease status of BL.

Burkitt lymphoma

Burkitt lymphoma (BL) is an aggressive form of B cell lymphoma that can affect children and adults. The study of BL led to the identification of the first recurrent chromosomal aberration in lymphoma, t(8;14)(q24;q32), and subsequent discovery of the central role of MYC and Epstein-Barr virus (EBV) in tumorigenesis. Most patients with BL are cured with chemotherapy but those with relapsed or refractory disease usually die of lymphoma. Historically, endemic BL, non-endemic sporadic BL and the immunodeficiency-associated BL have been recognized, but differentiation of these epidemiological variants is confounded by the frequency of EBV positivity. Subtyping into EBV⁺ and EBV^- BL might better describe the biological heterogeneity of the disease. Phenotypically resembling germinal centre B cells, all types of BL are characterized by dysregulation of MYC due to enhancer activation via juxtaposition with one of the three immunoglobulin loci. Additional molecular changes commonly affect B cell receptor and sphingosine-1-phosphate signalling, proliferation, survival and SWI-SNF chromatin remodelling. BL is diagnosed on the basis of morphology and high expression of MYC. BL can be effectively treated in children and adolescents with short durations of high dose-intensity multiagent chemotherapy regimens. Adults are more susceptible to toxic effects but are effectively treated with chemotherapy, including modified versions of paediatric regimens. The outcomes in patients with BL are good in high-income countries with low mortality and few late effects, but in low-income and middle-income countries, BL is diagnosed late and is usually treated with less-effective regimens affecting the overall good outcomes in patients with this lymphoma.

A Review of Cancer Genetics and Genomics Studies in Africa

Cancer is the second leading cause of death globally and is projected to overtake infectious disease as the leading cause of mortality in Africa within the next two decades. Cancer is a group of genomic diseases that presents with intra- and inter-population unique phenotypes, with Black populations having the burden of morbidity and mortality for most types. At large, the prevention and treatment of cancers have been propelled by the understanding of the genetic make-up of the disease of mostly non-African populations. By the same token, there is a wide knowledge gap in understanding the underlying genetic causes of, and genomic alterations associated with, cancer among black Africans. Accordingly, we performed a review of the literature to survey existing studies on cancer genetics/genomics and curated findings pertaining to publications across multiple cancer types conducted on African populations. We used PubMed MeSH terms to retrieve the relevant publications from 1990 to December 2019. The metadata of these publications were extracted using R text mining packages: RISmed and Pubmed.mineR. The data showed that only 0.329% of cancer publications globally were on Africa, and only 0.016% were on cancer genetics/genomics from Africa. Although the most prevalent cancers in Africa are cancers of the breast, cervix, uterus, and prostate, publications representing breast, colorectal, liver, and blood cancers were the most frequent in our review. The most frequently reported cancer genes were BRCA1, BRCA2, and TP53. Next, the genes reported in the reviewed publications’ abstracts were extracted and annotated into three gene ontology classes. Genes in the cellular component class were mostly associated with cell part and organelle part, while those in biological process and molecular function classes were mainly associated with cell process, biological regulation, and binding, and catalytic activity, respectively. Overall, this review highlights the paucity of research on cancer genomics on African populations, identified gaps, and discussed the need for concerted efforts to encourage more research on cancer genomics in Africa.

Epstein-Barr virus latent genes

Latent Epstein–Barr virus (EBV) infection has a substantial role in causing many human disorders. The persistence of these viral genomes in all malignant cells, yet with the expression of limited latent genes, is consistent with the notion that EBV latent genes are important for malignant cell growth. While the EBV-encoded nuclear antigen-1 (EBNA-1) and latent membrane protein-2A (LMP-2A) are critical, the EBNA-leader proteins, EBNA-2, EBNA-3A, EBNA-3C and LMP-1, are individually essential for in vitro transformation of primary B cells to lymphoblastoid cell lines. EBV-encoded RNAs and EBNA-3Bs are dispensable. In this review, the roles of EBV latent genes are summarized.

Epstein-Barr virus and Burkitt lymphoma

In 1964, a new herpesvirus, Epstein-Barr virus (EBV), was discovered in cultured tumor cells derived from a Burkitt lymphoma (BL) biopsy taken from an African patient. This was a momentous event that reinvigorated research into viruses as a possible cause of human cancers. Subsequent studies demonstrated that EBV was a potent growth-transforming agent for primary B cells, and that all cases of BL carried characteristic chromosomal translocations resulting in constitutive activation of the c-MYC oncogene. These results hinted at simple oncogenic mechanisms that would make Burkitt lymphoma paradigmatic for cancers with viral etiology. In reality, the pathogenesis of this tumor is rather complicated with regard to both the contribution of the virus and the involvement of cellular oncogenes. Here, we review the current understanding of the roles of EBV and c-MYC in the pathogenesis of BL and the implications for new therapeutic strategies to treat this lymphoma.

Epstein-Barr virus viral load and serology in childhood non-Hodgkin's lymphoma and chronic inflammatory conditions in Uganda: implications for disease risk and characteristics

Epstein-Barr virus (EBV) has been linked to malignancies and chronic inflammatory conditions. In this study, EBV detection was compared in children with non-Hodgkin's lymphoma and children with chronic inflammatory conditions, using samples and data from a case-control study carried out at the Mulago National Referral Hospital between 2004 and 2008. EBV viral load was measured in saliva, whole blood and white blood cells by real-time PCR. Serological values for IgG-VCA, EBNA1, and EAd-IgG were compared in non-Hodgkin's lymphoma and chronic inflammatory conditions; and in Burkitt's lymphoma and other subtypes of non-Hodgkin's lymphoma. Odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were calculated. Of the 127 children included (87 males and 40 females; median age 7 years, range 2-17), 96 had non-Hodgkin's lymphoma (46 Burkitt's lymphoma and 50 other non-Hodgkin's lymphoma), 31 had chronic inflammatory conditions, and only 10% were HIV-positive. The most common clinical presentations for all disease categories considered were fever, night sweats, and weight loss. EBV viral load in whole blood was elevated in Burkitt's lymphoma compared to other non-Hodgkin's lymphoma (OR 6.67, 95% CI 1.32, 33.69; P-value = 0.04), but EBV viral loads in saliva and white blood cells were not different in any of the disease categories considered. A significant difference in EAd-IgG was observed when non-Hodgkin's lymphoma was compared with chronic inflammatory conditions (OR 0.19, 95% CI 0.07, 0.51; P-value = 0.001). When compared to chronic inflammatory conditions, EBV viral load was elevated in Burkitt's lymphoma, and EA IgG was higher in non-Hodgkin's lymphoma. This study supports an association between virological and serological markers of EBV and childhood non-Hodgkin's lymphoma, irrespective of subtype, in Uganda.

EBV, HHV8 and HIV in B cell non Hodgkin lymphoma in Kampala, Uganda

BACKGROUND

B cell non Hodgkin lymphomas account for the majority of lymphomas in Uganda. The commonest is endemic Burkitt lymphoma, followed by diffuse large-B-cell lymphoma (DLBCL). There has been an increase in incidence of malignant lymphoma since the onset of the HIV/AIDS pandemic. However, the possible linkages of HHV8 and EBV to the condition of impaired immunity present in AIDS are still not yet very clearly understood.

OBJECTIVES

1. To describe the prevalence of Epstein-Barr virus, Human Herpes virus 8 and Human Immunodeficiency Virus-1 in B cell non Hodgkin lymphoma biopsy specimens in Kampala, Uganda.2. To describe the histopathology of non Hodgkin lymphoma by HIV serology test result in Kampala, Uganda

METHOD

Tumour biopsies specimens from 119 patients with B cell non Hodgkin lymphoma were classified according to the WHO classification. Immunohistochemistry was used for detection of HHV8 and in situ hybridization with Epstein Barr virus encoded RNA (EBER) for EBV. Real time and nested PCR were used for the detection of HIV.The patients from whom the 1991-2000 NHL biopsies had been taken did not have HIV serology results therefore 145 patients biopsies where serology results were available were used to describe the association of HIV with non Hodgkin lymphoma type during 2008-2009.

RESULTS

In this study, the majority (92%) of the Burkitt lymphomas and only 34.8% of the diffuse large B cell lymphomas were EBV positive. None of the precursor B lymphoblastic lymphomas or the mantle cell lymphomas showed EBV integration in the lymphoma cells.None of the Burkitt lymphoma biopsies had HIV by PCR. Of the 121 non Hodgkin B cell lymphoma patients with HIV test results, 19% had HIV. However, only 1(0.04%) case of Burkitt lymphoma had HIV. All the tumours were HHV8 negative.

CONCLUSIONS

The majority of the Burkitt lymphomas and two fifths of the diffuse large B cell lymphomas had EBV. All the tumours were HHV8 negative. Generally, the relationship of NHL and HIV was weaker than what has been reported from the developed countries. We discuss the role of these viruses in lymphomagenesis in light of current knowledge.

The high frequency of EBV infection in pediatric Hodgkin lymphoma is related to the classical type in Bahia, Brazil

Pediatric Hodgkin lymphoma (HL) occurring in developing regions is different from HL in industrialized countries due to the higher frequency of association with Epstein-Barr virus (EBV) infection. This infection is related to classical HL (cHL) but is virtually absent in nodular lymphocyte predominant HL (nLPHL). We studied the phenotype and the expression of EBV gene products in 90 pediatric cases by immunohistochemistry and in situ hybridization. EBV-positive tumor cells were found exclusively in cHL. The infection occurred with high frequency in all cHL subtypes, but it predominated in the mixed cellularity and lymphocyte depletion subtypes. These results reinforce the hypothesis that EBV plays a major role in the etiology of pediatric cHL in developing areas. Curiously, the frequency of EBV infection in HL was identical to the previously described for Burkitt's lymphoma in the same pediatric population. As both lymphomas have a postulated precursor cell in the germinal center (GC), the pattern of latently EBV-infected GC cells previously described in Bahia may be related to the development of these lymphomas.

Overview of Epstein-Barr virus-associated diseases in Japan

Epstein-Barr virus (EBV) associated diseases and studies performed in Japan are reviewed. Infectious mononucleosis is a common disease in Japanese infants. Chronic and severe EBV-infections include severe chronic active EBV-infection (SCAEBV), EBV-associated hemophagocytic syndrome, and mosquito allergy with granular lymphocyte proliferative disorder (GLPD). Autoimmune lymphoproliferative syndrome (ALPS), a disease caused by a defect in the Fas-Fas ligand pathway of cell-death, may develop into lymphoproliferative disease after early exposure to EBV. More than ten cases of X-linked lymphoproliferative syndrome (XLP) were discovered in Japanese children, and the frequency of post-transplant lymphoproliferative disorder (PTLD) increased after the number of patients receiving organ transplantation increased. Recently, an association of EBV with gastric carcinoma and hepatocellular carcinoma has been suggested. EBV-infected cells, such as B-cells, T-cells, NK-cells, and epithelial cells in EBV-associated diseases have also been clarified.

Cloned Shiga toxin 2 B subunit induces apoptosis in Ramos Burkitt's lymphoma B cells

The Shiga toxins (Stx1 and Stx2), produced by Shigella dysenteriae type 1 and enterohemorrhagic Escherichia coli, consist of one A subunit and five B subunits. The Stx1 and Stx2 B subunits form a pentameric structure that binds to globotriaosylceramide (Gb3-Cer) receptors on eukaryotic cells and promotes endocytosis. The A subunit then inhibits protein biosynthesis, which triggers apoptosis in the affected cell. In addition to its Gb3-Cer binding activity, the data in the following report demonstrate that the Stx2 B pentamer induces apoptosis in Ramos Burkitt's lymphoma B cells independently of A subunit activity. Apoptosis was not observed in A subunit-free preparations of the Stx1 B pentamer which competitively inhibited Stx2 B pentamer-mediated apoptosis. The pancaspase inhibitor, Z-VAD-fmk, prevented apoptosis in Ramos cells exposed to the Stx2 B subunit, Stx1 or Stx2. Brefeldin A, an inhibitor of the Golgi transport system, also prevented Stx2 B subunit-mediated apoptosis. These observations suggest that the Stx2 B subunit must be internalized, via Gb3-Cer receptors, to induce Ramos cell apoptosis. Moreover, unlike the two holotoxins, Stx2 B subunit-mediated apoptosis does not involve inhibition of protein biosynthesis. This study provides further insight into the pathogenic potential of this family of potent bacterial exotoxins.

CD40 ligand, Bcl-2, and Bcl-xL spare group I Burkitt lymphoma cells from CD77-directed killing via Verotoxin-1 B chain but fail to protect against the holotoxin

Owing to its lineage and differentiation stage-restricted expression, CD77 has been mooted as a therapeutic target in Burkitt lymphoma (BL). The recognition that the globotriaosyl moiety of this neutral glycosphingolipid is a receptor for Escherichia coli-derived Verotoxin-1 (Shiga-Like Toxin-1) offers a potential delivery system for the attack. Here we show that CD77-expressing Group I BL cells which are normally susceptible to activation-induced death on binding Verotoxin-1 B chain are protected in the presence of CD40 ligand. Ectopic expression of either bcl-2 or bcl-xL also afforded resistance to the actions of the B chain. In total contrast, neither of the survival genes nor a CD40 signal - even when acting in concert - protected against killing mediated by the holotoxin. These findings indicate that while therapeutic modalities for CD77-expressing B cell tumors (which include follicular lymphoma) based on the use of Verotoxin-1 B chain might be compromised by the activation of endogenous or exogenous survival pathways, those exploiting the holotoxin should be left unscathed.

The A20 protein interacts with the Epstein-Barr virus latent membrane protein 1 (LMP1) and alters the LMP1/TRAF1/TRADD complex

The Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) interacts with the tumor necrosis factor receptor (TNFR)-associated factor (TRAF) molecules, which are important for LMP1-mediated signaling. Two domains of LMP1 can independently activate NF-kB, carboxyl-terminal activating region 1 (CTAR1) and CTAR2. The activation of NF-kB by CTAR1 occurs through direct interaction of LMP1 with the TRAF molecules, whereas CTAR2 interacts with the TNFR-associated death domain protein (TRADD) to activate NF-kB and the c-Jun N-terminal kinase (JNK). A20, which is induced by LMP1 through NF-kB, can block NF-kB activation from both domains of LMP1 and inhibit JNK activation from CTAR2. A20 also has been shown to associate with TRAF1 and TRAF2. In this study, an interaction between LMP1 and A20 was detected that was increased by TRAF2 overexpression. A20 did not affect the association of TRAF1 with TRAF2 but did displace TRAF1 from the LMP1 complex. The interaction of LMP1 and TRADD was decreased in the presence of A20, and the LMP1-A20 association was decreased by TRADD, suggesting that A20 and TRADD both interact with LMP1 and may compete for binding. These data indicate that A20 alters the interactions between LMP1 and the TRAF molecules and TRADD, affecting the activation of NF-kB, JNK, and perhaps other TRAF-mediated signaling events.

Prolonged Phenotypic, Functional, and Molecular Change in Group I Burkitt Lymphoma Cells on Short-Term Exposure to CD40 Ligand

Group I Burkitt lymphoma (BL) cell lines (L3055, Elijah, Louckes, BL2, and BL29) retaining the original biopsy phenotype were found to undergo prolonged phenotypic, functional, and molecular change on short-term exposure to soluble recombinant CD40L trimer. Sensitivity to, extent of, and duration of change appeared to reflect passage number in that the earliest passaged lines, L3055 and BL29, were generally the most susceptible. Culture of group I BL lines with CD40L resulted in significant growth arrest (without apoptosis) that, for L3055 cells, was sustained for 7 to 9 days after 72 hours of exposure. This was accompanied by the formation of large homotypic aggregates together with gross changes in individual cell morphology and a concomitant upregulation of CD54 (ICAM-1). Three of the five group I BL lines exhibited rapid downregulation of the hallmark CD77 surface antigen, which, for L3055 cells, was maintained for at least 12 days after 72 hours of incubation with CD40L. With the exception of BL2, all group I BL lines were induced to express CD40 homodimers on CD40-stimulation, whereas only monomers were detected in unstimulated cells. Experiments using CD40-transfected Rat-1 fibroblasts showed that the ability to signal for dimer formation required Thr234of CD40. For L3055 and BL29 cells, an initial 72 hours of exposure to CD40L resulted in the maintenance of homodimers for up to 14 and 10 days, respectively. There was a close correlation between the induction and duration of CD40 homodimers and the appearance of Bcl-2. For L3055 cells, which are sensitive to apoptosis-induction on BCR-engagement, exposure to CD40L for 72 hours was found to provide considerable protection from anti-IgM, which was still significant to 20 days. The implications of such sustained effects on relatively short-term exposure of tumor B cells to CD40L are discussed.

© 1998 by The American Society of Hematology.

Prolonged Phenotypic, Functional, and Molecular Change in Group I Burkitt Lymphoma Cells on Short-Term Exposure to CD40 Ligand

Group I Burkitt lymphoma (BL) cell lines (L3055, Elijah, Louckes, BL2, and BL29) retaining the original biopsy phenotype were found to undergo prolonged phenotypic, functional, and molecular change on short-term exposure to soluble recombinant CD40L trimer. Sensitivity to, extent of, and duration of change appeared to reflect passage number in that the earliest passaged lines, L3055 and BL29, were generally the most susceptible. Culture of group I BL lines with CD40L resulted in significant growth arrest (without apoptosis) that, for L3055 cells, was sustained for 7 to 9 days after 72 hours of exposure. This was accompanied by the formation of large homotypic aggregates together with gross changes in individual cell morphology and a concomitant upregulation of CD54 (ICAM-1). Three of the five group I BL lines exhibited rapid downregulation of the hallmark CD77 surface antigen, which, for L3055 cells, was maintained for at least 12 days after 72 hours of incubation with CD40L. With the exception of BL2, all group I BL lines were induced to express CD40 homodimers on CD40-stimulation, whereas only monomers were detected in unstimulated cells. Experiments using CD40-transfected Rat-1 fibroblasts showed that the ability to signal for dimer formation required Thr234of CD40. For L3055 and BL29 cells, an initial 72 hours of exposure to CD40L resulted in the maintenance of homodimers for up to 14 and 10 days, respectively. There was a close correlation between the induction and duration of CD40 homodimers and the appearance of Bcl-2. For L3055 cells, which are sensitive to apoptosis-induction on BCR-engagement, exposure to CD40L for 72 hours was found to provide considerable protection from anti-IgM, which was still significant to 20 days. The implications of such sustained effects on relatively short-term exposure of tumor B cells to CD40L are discussed.

© 1998 by The American Society of Hematology.

Identification of a novel protein encoded by the BamHI A region of the Epstein-Barr virus

An unusual set of 3' coterminal, spliced mRNAs transcribed through the BamHI A fragment have been previously identified in nasopharyngeal carcinoma (NPC) tissues. These RNAs have also been detected at low levels in Burkitt's lymphoma (BL) cell lines and Epstein-Barr virus (EBV)-transformed lymphocytes. Sequence analyses of clones from a cDNA library derived from the C15 NPC tumor indicated that the primary transcripts are differentially spliced, giving rise to a family of related transcripts, all of which encompass the BARF0 open reading frame (ORF) at the 3' end of the transcripts. One cDNA was identified that extended the BARF0 ORF at the 5' end, forming the RK-BARF0 ORF. In this study, a rabbit antiserum to a synthetic peptide representing an amino acid sequence encoded by the BARF0 ORF was prepared. This antiserum detected a glutathione S-transferase-BARF0 fusion protein and both BARF0 and RK-BARF0 proteins expressed from transfected constructs in H1299 cells. The serum also immunoprecipitated the 20-kDa BARF0 and 30-kDa RK-BARF0 in vitro-translated proteins. Immunoblot analyses identified a protein doublet of 30 and 35 kDa in all of the EBV-infected cell lines tested. Cellular fractionation studies revealed that the proteins were membrane associated. The sizes of the proteins detected in cell lines and their association with membranes suggests that they are likely encoded by the RK-BARF0 transcript, which is predicted to contain a membrane localization signal. The proteins were also detected in protein extracts prepared from NPC biopsies and a BL biopsy but not from hairy leukoplakia, a permissive EBV infection. These results reveal that the rightward RNA transcripts from the BamHI A region of EBV encode one or more proteins that are expressed in latently infected cells and in tumor tissue.

Epstein-Barr virus latent membrane protein 1 blocks p53-mediated apoptosis through the induction of the A20 gene

Two Epstein-Barr virus (EBV)-associated malignancies, nasopharyngeal carcinoma and posttransplant lymphoma, rarely have mutations in the p53 tumor suppressor gene, suggesting that a viral protein interferes with p53 function. The EBV oncogene, LMP1, induces expression of the cellular antiapoptotic genes bcl-2 and A20 and could in this way interfere with p53-mediated apoptosis. Two derivatives of the p53-null epithelial cell line H1299 were prepared, one of which (H1299-p53) stably expressed a temperature-sensitive (ts) p53 protein, and another (H1299-p53+LMP1) which stably expressed both ts-p53 and latent membrane protein 1 (LMP1). At the permissive temperature, the p53 protein in the H1299-p53 cell line transcriptionally activated two of its target genes, the cyclin-dependent kinase inhibitor p21 and the mdm2 gene product, in an LMP1-independent manner. Upon serum withdrawal at the permissive temperature, p53-mediated apoptosis was induced in 50 to 60% of the cells. In the H1299-p53 cell line which stably expressed LMP1, however, only 20 to 25% of the cells underwent apoptosis. While stable expression of LMP1 did not affect levels of bcl-2 family members in these cells, it did induce expression of A20. Stable expression of A20 in the H1299-p53 cell line inhibited p53-mediated apoptosis equivalent to inhibition by LMP1. The induction of A20 may underlie the ability of LMP1 to protect EBV-infected epithelial cells from p53-mediated apoptosis.

The investigation of Epstein-Barr viral sequences in 41 cases of Burkitt's lymphoma from Egypt: epidemiologic correlations

BACKGROUND

Epstein-Barr virus (EBV) is associated with many human neoplasms, including Burkitt's lymphoma (BL). Endemic BL in central Africa is more often EBV-associated than BL in the United States, where seroconversion for EBV occurs somewhat later than in Africa. Therefore, the EBV association rate in BL may correlate more with the socioeconomic status of the population studied, which influences the age of EBV seroconversion, than with such factors as malaria, which may relate to the overall higher incidence rate in endemic regions.

METHODS

Forty-one patients with BL in Egypt, which differs both climatically and racially from central African countries (i.e., Kenya, Uganda) where BL is endemic, were analyzed. All biopsies were evaluated for EBV-encoded RNAs (EBER1) by RNA in situ hybridization, analyzed for p53 protein expression using the monoclonal antibody D07, and immunophenotyped using a panel of monoclonal antibodies that included L26 (CD20), Leu 22 (CD43), and A6 (CD45RO). Twelve cases were evaluable for EBV subtype by polymerase chain reaction with EBV-specific primers.

RESULTS

The median age at diagnosis was 9 years (range, 2-22 years). The biopsy site was extranodal in 29 patients and nodal in 12 patients. All 41 cases were documented as B-cell neoplasms. A hybridization signal for EBER1 RNA was identified in greater than 95% of the neoplastic cells in 30 of 41 cases (73%), whereas no signal was observed in 11 cases (27%). Epstein-Barr virus subtype 1 was found in 10 patients, subtype 2 in two patients. Immunostaining for p53 was observed in greater than 5% of the neoplastic cells in 9 of 37 cases (24%). No significant correlation was observed between EBV positivity and sex, biopsy site, or p53 immunostaining.

CONCLUSIONS

The prevalence of EBV in BL from Egypt is slightly lower than in BL in endemic regions, but significantly higher than in sporadic BL. Epstein-Barr virus positivity probably reflects the socioeconomic status of the patient population, and age at seroconversion. The prevalence of EBV subtype 1 suggests that immunodeficiency does not play a role in Egyptian Burkitt's lymphoma, in contrast to endemic Burkitt's lymphoma, in which holoendemic malaria is thought to contribute to immunodeficiency, a higher incidence rate, and the observed prevalence of subtype 2.

Immune regulation in Epstein-Barr virus-associated diseases

Epstein-Barr virus (EBV) is a member of the human herpesvirus family and, like many other herpesviruses, maintains a lifelong latent association with B lymphocytes and a permissive association with stratified epithelium in the oropharynx. Clinical manifestations of primary EBV infection range from acute infectious mononucleosis to an asymptomatic persistent infection. EBV is also associated with a number of malignancies in humans. This review discusses features of the biology of the virus, both in cell culture systems and in the natural host, before turning to the role of the immune system in controlling EBV infection in healthy individuals and in individuals with EBV-associated diseases. Cytotoxic T cells that recognize virally determined epitopes on infected cells make up the major effector arm and control the persistent infection. In contrast, the options for immune control of EBV-associated malignancies are more restricted. Not only is antigen expression restricted to a single nuclear antigen, EBNA1, but also these tumor cells are unable to process EBV latent antigens, presumably because of a transcriptional defect in antigen-processing genes (such as TAP1 and TAP2). The likelihood of producing a vaccine capable of controlling the acute viral infection and EBV-associated malignancies is also discussed.

Alterations of the p53 gene in Epstein-Barr virus-associated immunodeficiency-related lymphomas

Mutations of the p53 tumor suppressor gene are among the most common genetic alterations found in many different human malignancies, including those of the colon, lung, and breast. Alterations in wild-type p53 lead to loss of the suppressor function and thus contribute to tumorigenesis. The potential role of p53 mutations in a sampling of B-cell lymphomas, the majority of which were associated with Epstein-Barr virus (EBV), was investigated. Twenty-six biopsy specimens from immunocompromised patients, including allograft recipients and patients with AIDS, Wiscott-Aldrich syndrome, and human T-cell leukemia virus type 1 infection, in comparison with three Burkitt lymphomas and four Burkitt lymphoma cell lines were analyzed. Mutation in p53 was detected in all four Burkitt lymphoma cell lines as well as the three Burkitt lymphoma biopsy specimens. In patients with AIDS, 5 of 10 lymphomas were EBV positive, and 1 had a mutation in p53. Mutation in p53 was not detected in 14 EBV-positive lymphomas which arose in transplant recipients. These data indicate that with the exception of Burkitt lymphomas, p53 mutations are not involved in the majority EBV-positive B-cell lymphomas which develop in immunocompromised patients.

Are plant factors a missing link in the evolution of endemic Burkitt's lymphoma?

Burkitt's lymphoma, an Epstein-Barr virus (EBV)-associated non-Hodgkin's malignant lymphoma is endemic in an area of Africa known as the Lymphoma Belt. This zone is demarcated by climatic requirements of temperature and rainfall. EBV-activating plant factors are among several co-factors which have been proposed for the development of epidemic Burkitt's Lymphoma (eBL). The distribution of Euphorbia tirucalli, a plant which possesses EBV-activating substances and can induce the characteristic 8:14 translocation of eBL in EBV-infected lymphoblastic cell lines in vitro, conforms closely to the climatic requirements of the Lymphoma. This plant, other EBV-activating plants and plants of unknown EBV-activating status with medicinal uses, are found significantly more often at the homes of eBL patients in Malawi than in those of controls. The possible role of these plant factors in the pathogenesis of eBL and their routes of bodily access are discussed. It is postulated that the associations described in this paper provide support for the theory that EBV-activating plants are co-factors involved in the pathogenesis of some cases of eBL.

Viral oncogenesis: Epstein-Barr virus

The Epstein-Barr virus (EBV) is a common herpesvirus that has been linked to several human neoplasms. It has been found in over 90% of cases of Burkitt's lymphoma in endemic regions, although only 15% of cases in nonendemic regions show evidence of infection. The virus has been found in malignant lymphomas in immunocompromised states, including the acquired immunodeficiency syndrome, iatrogenic immunosuppression, such as in posttransplantation patients, and congenital immunodeficiencies. Recently, EBV genomes have been found in approximately 25% of cases of Hodgkin's disease, where it has been found in the Reed-Sternberg cells. Epstein-Barr virus genomes are found in over 90% of cases of undifferentiated nasopharyngeal carcinoma. In addition, EBV has been identified in undifferentiated carcinomas in other sites in Asians, such as carcinomas of the parotid in Chinese individuals and Eskimos.

High interferon titer and defective NK-cell activity in the circulation of nasopharyngeal carcinoma patients

The interferon (IFN) activity of sera from 19 patients with nasopharyngeal carcinoma (NPC) was determined by the plaque-reduction assay with vesicular stomatitis virus (VSV) in HeLa cells and compared to that of sera from matched healthy controls. High titers of interferon were detected in the sera of the NPC patients with a geometric mean titer (GMT) of 43 +/- 25 U/ml. The interferon activity of the patients' sera was acid- and heat-labile (pH = 2 and 56 degrees C for 1 hr) and could be neutralized by a goat antiserum to human IFN-gamma. Interferon titers of the patients, in contrast, to normal controls, were not correlated with natural killer (NK) activity which was abnormally low in the NPC patients. On the other hand, a high percentage of circulating cells co-expressing the LGL marker (HNK-I) and the OKT8 antigen was detected in parallel with high IFN levels in NPC patients.

Epstein-Barr virus status and tumour cell phenotype in sporadic Burkitt's lymphoma

Burkitt's lymphoma (BL) biopsy cells and derived cell lines can be grouped according to their patterns of reactivity with 6 selected monoclonal antibodies (MAbs) against B cell-associated surface antigens. Group I cells react only with MAbs J5 and 38.13, recognising the common acute lymphoblastic leukaemia antigen and a BL-associated antigen respectively; group II cells react with J5 and 38.13 and with one or more of a set of MAbs (Ki-24, MHM6, AC2, Ki-1) against "lymphoblastoid" antigens; group III cells react only with these anti-"lymphoblastoid" MAbs. Tumour biopsy cells from 17 cases of sporadic BL, 9 positive for the Epstein-Barr (EB) virus genome and 8 negative, have been analysed during the process of cell line establishment in vitro. In early passage the EB virus-negative BL cells showed either a group I phenotype or gave an additional reactivity with MAb Ki-24 which placed them in group II; these phenotypes remained essentially stable with continued growth of the cell lines for up to 50 passages. By contrast the EB virus-positive BL cells were much more susceptible to phenotypic change in vitro. Although such cells displayed a group I or group II phenotype in early passage, many of the lines soon moved into group III whilst retaining the karyotypic markers indicative of their malignant origin. These observations suggest that a resident EB virus genome can drive the in vitro progression of BL cells towards a more "lymphoblastoid" phenotype. This was confirmed in subsequent experiments where virus-negative BL cell lines were converted to EB virus positivity by in vitro infection. Clearly, therefore, phenotypic analysis of long-established lines can lead to false distinctions being drawn between the EB virus-positive and -negative forms of sporadic BL; both may derive from the same sub-population of target B cells in vivo.

No evidence for differences in the Epstein-Barr virus genome carried in Burkitt lymphoma cells and nonmalignant lymphoblastoid cells from the same patients

Epstein-Barr virus (EBV), although not an indispensable factor for the development of Burkitt lymphoma, is apparently associated with the 20-fold higher incidence of the disease in Equatorial Africa compared to the incidence in other parts of the world. To determine whether different EBV subtypes are associated with the appearance of the malignant phenotype, we have compared the EBV genomes carried in the Burkitt tumor cells with those carried in the nonmalignant lymphoblastoid cells from the same individuals. From three patients with EBV -associated Burkitt lymphoma, tumor cell lines as well as spontaneously established lymphoblastoid cell lines representing the nonmalignant counterparts were obtained. The viral DNA in these cell lines was analyzed by Southern blot hybridization, using a set of cloned EBV DNA fragments as probes that recognize polymorphic regions in the viral genome. Using a number of different polymorphic markers to distinguish one isolate from another, the virus genome found in the tumor cells could also be identified in the nonmalignant cells of the same patient. In one case, in which two independent lymphoblastoid cell lines were established, evidence was obtained that this patient was infected by at least two distinct EBV subtypes. These results strongly suggest that in Burkitt lymphoma, the risk associated with EBV is related to cofactors such as chronic malaria and the mode of infection rather than to peculiar viral subtypes. The situation seems to be totally different from papillomavirus-associated diseases, in which the risk of progression to malignancy appears to be associated with particular viral strains.

Expression of HLA-DR antigens in nasopharyngeal carcinoma: an immunohistological analysis of the tumour cells and infiltrating lymphocytes

A panel of conventional and monoclonal antibodies was used to examine the immunohistological characteristics of malignant epithelial cells and infiltrating lymphocytes in frozen sections of nasopharyngeal carcinoma (NPC) biopsies from 10 Tunisian patients. Three main categories of cells were identified. (1) Tumour cells which were positive for Epstein-Barr nuclear antigen, HLA-ABC and keratin determinants. In most samples, the tumour cells also expressed variable amounts of HLA-DR antigens. The presence of HLA-DR antigens has not been previously reported in NPC and may be a contributory factor in effecting the transfer of Epstein-Barr virus to the epithelial cells. (2) Infiltrating lymphocytes which were mainly composed of T inducer (T4+) and T suppressor/cytotoxic (T8+) cells although one sample contained predominantly immature T cells expressing the HTA-I+ cortical thymocyte phenotype. Few B cells or natural killer cells were demonstrated. (3) Large HTA-I+ dendritic cells which were invariably present within the tumour masses. These were morphologically and phenotypically similar to antigen presenting Langerhans cells which are usually located in the skin but also found in other epithelial sites. These cells may be a residual population from the normal nasopharynx or represent part of a specific immunological response to the presence of Epstein-Barr virus in the epithelial cells.

Abdominal Burkitt-type lymphomas in Algeria

In a previous retrospective analysis from the principal paediatric centres of Algeria, Burkitt-type lymphomas (BL) were shown to account for around 46.5% of the total childhood non-Hodgkin's malignant lymphomas in that country. In the present study, a series of 49 abdominal BL from the Paediatric Clinic of Surgery, Mustapha Hospital, Algiers, has been studied. The age distribution shows a peak between 4 and 5 years of age, and the sex ratio is (M:F) 2.26:1. The disease is characterized by a rapid evolution in the absence of therapy. The major problem is an explosive form of the disease, which at present seems difficult to control in this country. Fifteen of the 49 patients (30.6%) died before completion of the first course of chemotherapy; however, complete remission (CR) was obtained for 30 patients (61%). Overall survival was 42.85% (21/49), whereas survival of patients who reached CR is 70% (21/30). When CR was obtained, deaths were related to cerebrospinal fluid involvement, local recurrence, secondary bone marrow involvement or therapeutic accidents. All patients alive with no evidence of disease (NED) 8-months after CR can be considered definitively cured. Epstein-Barr virus (EBV) serology performed on 31 BL patients and on a control group of 25 children with other malignant tumours showed that most Algerian BL have elevated EBV titres. A search for viral markers within malignant cells in 17 patients indicated that 88% (15/17) of the BL cases were EBV-associated. Analysis of the immunological and cytogenetic data showed that, as in the rest of the world, these BL cases involve proliferation of B-cell-type lymphocytes, with characteristic cytogenetic translocations involving chromosome 8. This report represents the most detailed description so far of BL from an area in non-equatorial Africa and the first report of a large series from North Africa.