Epstein Barr virus-associated tumours: an update for the attention of the working pathologist

Epstein-Barr virus (EBV) is a herpesvirus associated with approximately 1% of tumours worldwide. EBV is the epitome of B lymphotropic viruses, but the spectrum of tumours it is associated with extends to T lymphocyte and NK cell malignancies, various types of carcinomas and smooth muscle tumours. Ubiquitous EBV infection in humans implies that most individuals carry EBV-infected cells. Therefore, mere detection of the virus in individuals with a tumour is not sufficient for establishing a causal relationship between both events, but instead requires unequivocal detection of viral nucleic acids or viral proteins in the tumour cells. Recent controversies about EBV infection in several carcinomas mainly resulted from such technical issues. The gold standard remains in situ EBER detection, but detection of EBNA1 would be an interesting alternative. EBV detection can be helpful for diagnostic, prognostic and therapeutic purposes. The rate of EBV association with entities such as NK/T cell tumours of the nasal type is so high that absence of detection of the virus in such a lesion should cast doubt of the accuracy of the diagnosis. Similarly, diagnosis of EBV-associated follicular pseudo-tumour obviously requires detection of the virus. EBV-positive common gastric adenocarcinomas seem to have a better prognosis than their EBV-negative counterparts and identification of the virus in B cell lymphoproliferations in immunocompromised individuals will guide therapeutic options. In conclusion, EBV-associated tumours are common enough to be relevant for the pathologist in everyday practice, but there is a need to facilitate detection of the virus (eg EBNA1 antibody).

Epstein-Barr virus BNRF1 protein allows efficient transfer from the endosomal compartment to the nucleus of primary B lymphocytes

Epstein-Barr virus (EBV) is a tumor virus with marked B lymphotropism. After crossing the B-cell membrane, the virus enters cytoplasmic vesicles, where decapsidation takes place to allow transfer of the viral DNA to the cell nucleus. BNRF1 has been characterized as the EBV major tegument protein, but its precise function is unknown. We have constructed a viral mutant that lacks the BNRF1 gene and report here its in vitro phenotype. A recombinant virus devoid of BNRF1 (DeltaBNRF1) showed efficient DNA replication and production of mature viral particles. B cells infected with the DeltaBNRF1 mutant presented viral lytic antigens as efficiently as B cells infected with wild-type or BNRF1 trans-complemented DeltaBNRF1 viruses. Antigen presentation in B cells infected with either wild-type (EBV-wt) or DeltaBNRF1 virus was blocked by leupeptin addition, showing that both viruses reach the endosome/lysosome compartment. These data were confirmed by direct observation of the mutant virus in endosomes of infected B cells by electron microscopy. However, we observed a 20-fold reduction in the number of B cells expressing the nuclear protein EBNA2 after infection with a DeltaBNRF1 virus compared to wild-type infection. Likewise, DeltaBNRF1 viruses transformed primary B cells much less efficiently than EBV-wt or BNRF1 trans-complemented viruses. We conclude from these findings that BNRF1 plays an important role in viral transport from the endosomes to the nucleus.

Defective infectious particles and rare packaged genomes produced by cells carrying terminal-repeat-negative epstein-barr virus

The Epstein-Barr virus (EBV) lytic program includes lytic viral DNA replication and the production of a viral particle into which the replicated viral DNA is packaged. The terminal repeats (TRs) located at the end of the linear viral DNA have been identified as the packaging signals. A TR-negative (TR(-)) mutant therefore provides an appropriate tool to analyze the relationships between EBV DNA packaging and virus production. Here, we show that supernatants from lytically induced 293 cells carrying TR mutant EBV genomes (293/TR(-)) contain large amounts of viral particles devoid of viral DNA which are nevertheless able to bind to EBV target cells. This shows that viral DNA packaging is not a prerequisite for virion formation and egress. Rather surprisingly, supernatants from lytically induced 293/TR(-) cells also contained rare infectious viruses carrying the viral mutant DNA. This observation indicates that the TRs are important but not absolutely essential for virus encapsidation.

Low level of lytic replication in a recombinant Epstein-Barr virus carrying an origin of replication devoid of BZLF1-binding sites

Binding of the BZLF1 viral transactivator to Epstein-Barr virus (EBV) oriLyt has been reported to be essential for viral DNA replication. We have constructed a recombinant virus (E2-oriLyt-R) in which the oriLyt BZLF1-binding sites (ZRE) were exchanged against papilloma E2-binding sites. A fusion protein between the BZLF1 protein-transactivating domain and the E2 protein-binding domain was able to reactivate lytic replication in E2-oriLyt-R. However, BZLF1 alone could also induce E2-oriLyt-R, albeit with much lower efficiency. ZRE are therefore important but not absolutely essential cis elements for lytic replication. This shows the importance of recombinants to evaluate viral functions.

Glycoprotein gp110 of Epstein-Barr virus determines viral tropism and efficiency of infection

The Epstein-Barr virus (EBV) genome has been detected in lymphomas and in tumors of epithelial or mesenchymal origin such as nasopharyngeal carcinoma or leiomyosarcoma. Thus, there is little doubt that EBV can infect cells of numerous lineages in vivo, in contrast to its in vitro infectious spectrum, which appears restricted predominantly to B lymphocytes. We show here that the EBV BALF4 gene product, the glycoprotein gp110, dramatically enhances the ability of EBV to infect human cells. gp110(high) viruses were up to 100 times more efficient than their gp110(low) counterparts in infecting lymphoid or epithelial cells. In addition, gp110(high) viruses infected the carcinoma cell line HeLa and the T cell lymphoma cell line Molt-4, both previously thought to be refractory to EBV infection. Analysis of several virus isolates showed that the amount of BALF4 present within mature virions markedly differed among these strains. In some strains, gp110 was found expressed during lytic replication not only at the nuclear but also at the cellular membrane. Heterologous expression of gp110 during the virus lytic phase neither altered virus concentration nor affected virus binding to cells. It appears that gp110 plays a crucial role after the virus has adhered to its cellular target. gp110 constitutes an important virulence factor that determines infection of non-B cells by EBV. Therefore, the use of gp110(high) viruses will help to determine the range of the target cells of EBV beyond B lymphocytes and provide a useful in vitro model to assess the oncogenic potential of EBV in these cells.

Identification of acidic and aromatic residues in the Zta activation domain essential for Epstein-Barr virus reactivation

Epstein-Barr virus (EBV) lytic cycle transcription and DNA replication require the transcriptional activation function of the viral immediate-early protein Zta. We describe a series of alanine substitution mutations in the Zta activation domain that reveal two functional motifs based on amino acid composition. Alanine substitution of single or paired hydrophobic aromatic amino acid residues resulted in modest transcription activation defects, while combining four substitutions of aromatic residues (F22/F26/W74/F75) led to more severe transcription defects. Substitution of acidic amino acid residue E27, D35, or E54 caused severe transcription defects on most viral promoters. Promoter- and cell-specific defects were observed for some substitution mutants. Aromatic residues were required for Zta interaction with TFIIA-TFIID and the CREB-binding protein (CBP) and for stimulation of CBP histone acetyltransferase activity in vitro. In contrast, acidic amino acid substitution mutants interacted with TFIIA-TFIID and CBP indistinguishably from the wild type. The nuclear domain 10 (ND10) protein SP100 was dispersed by most Zta mutants, but acidic residue mutations led to reduced, while aromatic substitution mutants led to increased SP100 nuclear staining. Acidic residue substitution mutants had more pronounced defects in transcription activation of endogenous viral genes in latently infected cells and for viral replication, as measured by the production of infectious virus. One mutant, K12/F13, was incapable of stimulating EBV lytic replication but had only modest transcription defects. These results indicate that Zta stimulates viral reactivation through two nonredundant structural motifs, one of which interacts with general transcription factors and coactivators, and the other has an essential but as yet not understood function in lytic transcription.

Epstein-Barr virus infection and human malignancies

The Epstein-Barr virus (EBV) is a herpes virus which establishes a life-long persistent infection in over 90% of the human adult population world-wide. Based on its association with a variety of lymphoid and epithelial malignancies, EBV has been classified as a group 1 carcinogen by the International Agency for Research on Cancer. In this article we discuss the evidence supporting an aetiological role for EBV in the pathogenesis of human tumours. The biology of EBV infection will be described with special emphasis on viral transforming gene products. A brief survey of EBV-associated tumours is followed by a discussion of specific problems. Evidence is presented which suggests that failures of the EBV-specific immunity may play a role in the pathogenesis of EBV-associated tumours also in patients without clinically manifest immunodeficiencies. Finally, the timing of EBV infection in the pathogenesis of virus-associated malignancies is discussed. There is good evidence that EBV infection precedes expansion of the malignant cell populations in some virus-associated tumours. However, this is clearly not always the case and for some of these tumours there are indications that clonal genetic alterations may occur prior to EBV infection. Thus, whilst there is good evidence to suggest that EBV is a human carcinogen, its precise role(s) in the development of virus-associated human tumours requires clarification.

Epstein-Barr virus infection and human malignancies

The Epstein-Barr virus (EBV) is a herpes virus which establishes a life-long persistent infection in over 90% of the human adult population world-wide. Based on its association with a variety of lymphoid and epithelial malignancies, EBV has been classified as a group 1 carcinogen by the International Agency for Research on Cancer. In this article we discuss the evidence supporting an aetiological role for EBV in the pathogenesis of human tumours. The biology of EBV infection will be described with special emphasis on viral transforming gene products. A brief survey of EBV-associated tumours is followed by a discussion of specific problems. Evidence is presented which suggests that failures of the EBV-specific immunity may play a role in the pathogenesis of EBV-associated tumours also in patients without clinically manifest immunodeficiencies. Finally, the timing of EBV infection in the pathogenesis of virus-associated malignancies is discussed. There is good evidence that EBV infection precedes expansion of the malignant cell populations in some virus-associated tumours. However, this is clearly not always the case and for some of these tumours there are indications that clonal genetic alterations may occur prior to EBV infection. Thus, whilst there is good evidence to suggest that EBV is a human carcinogen, its precise role(s) in the development of virus-associated human tumours requires clarification.

Spontaneous activation of the lytic cycle in cells infected with a recombinant Kaposi's sarcoma-associated virus

The genetic analysis of human herpesvirus 8 (HHV8), also termed Kaposi's sarcoma-associated virus, has been hampered by severe difficulties in producing infectious viral particles and modifying the viral genome. In this article, we report the successful cloning of the HHV8 complete genome onto a prokaryotic F-plasmid replicon which allows the propagation of the recombinant viral DNA in Escherichia coli. The insertion of the F-plasmid into the HHV8 genome interrupts the ORF56 gene, whose expression product-by homology with the Epstein-Barr virus BSLF1 gene--is supposed to be necessary for lytic DNA replication. After introduction of the recombinant HHV8 DNA into 293 cells, early viral antigens are expressed, suggesting that spontaneous lytic replication is initiated. However, completion of the lytic program is prevented by the absence of the ORF56 protein, and a quasi-latent state is established. Upon reintroduction of the ORF56 viral gene, the block is overcome and infectious HHV8 virions are produced. As the recombinant HHV8 genome can be easily modified in E. coli, this experimental system opens the way to an extensive genetic analysis of other HHV8 functions.

Infectious Epstein-Barr virus lacking major glycoprotein BLLF1 (gp350/220) demonstrates the existence of additional viral ligands

The binding of the viral major glycoprotein BLLF1 (gp350/220) to the CD21 cellular receptor is thought to play an essential role during infection of B lymphocytes by the Epstein-Barr virus (EBV). However, since CD21-negative cells have been reported to be infectible with EBV, additional interactions between viral and cellular molecules seem to be probable. Based on a recombinant genomic EBV plasmid, we deleted the gene that encodes the viral glycoprotein BLLF1. We tested the ability of the viral mutant to infect different lymphoid and epithelial cell lines. Primary human B cells, lymphoid cell lines, and nearly all of the epithelial cell lines that are susceptible to wild-type EBV infection could also be successfully infected with the viral mutant in vitro, although the efficiency of infection with BLLF1-negative virus was clearly lower than the one observed with wild-type EBV. Our studies show that the interaction between BLLF1 and CD21 is not absolutely required for the infection of lymphocytes and epithelial cells, indicating that viral molecules other than BLLF1 can mediate the binding of EBV to its target cells. In this context, our results further suggest the hypothesis that additional cellular molecules, apart from CD21, allow virus entry into these cells.

The genetic approach to the Epstein-Barr virus: from basic virology to gene therapy

The Epstein-Barr virus (EBV) infects humans and the genome of this infectious agent has been detected in several tumour types, ranging from lymphomas to carcinomas. The analysis of the functions of the numerous viral proteins encoded by EBV has been impeded by the large size of the viral genome, which renders the construction of viral mutants difficult. To overcome these limitations, several genetic systems have been developed that allow the modification of the viral genome. Two different approaches, depending on the host cell type in which the viral mutants are generated, have been used in the past. Traditionally, mutants were constructed in EBV infected eukaryotic cells, but more recently, approaches that make use of a recombinant EBV cloned in Escherichia coli have been proposed. The phenotype associated with the inactivation or modification of nearly 20 of the 100 EBV viral genes has been reported in the literature. In most of the reported cases, the EBV latent genes that mediate the ability of EBV to immortalize infected cells were the targets of the genetic analysis, but some virus mutants in which genes involved in DNA lytic replication or infection were disrupted have also been reported. The ability to modify the viral genome also opens the way to the construction of viral strains with medical relevance. A cell line infected by a virus that lacks the EBV packaging sequences can be used as a helper cell line for the encapsidation of EBV based viral vectors. This cell line will allow the evaluation of EBV as a gene transfer system with applications in gene therapy. Finally, genetically modified non-pathogenic strains will provide a basis for the design of an attenuated EBV live vaccine.

The Epstein-Barr virus lytic program is controlled by the co-operative functions of two transactivators

The propagation of herpesviruses has long been viewed as a temporally regulated sequential process that results from the consecutive expression of specific viral transactivators. As a key step in this process, lytic viral DNA replication is considered as a checkpoint that controls the expression of the late structural viral genes. In a novel genetic approach, we show that both hypotheses do not hold true for the Epstein-Barr virus (EBV). The study of viral mutants of EBV in which the early genes BZLF1 and BRLF1 are deleted allowed a precise assignment of the function of these proteins. Both transactivators were absolutely essential for viral DNA replication. Both BZLF1 and BRLF1 were required for full expression of the EBV proteins expressed during the lytic program, although the respective influence of these molecules on the expression of various viral target genes varied greatly. In replication-defective viral mutants, neither early gene expression nor DNA replication was a prerequisite for late gene expression. This work shows that BRLF1 and BZLF1 harbor distinct but complementary functions that influence all stages of viral production.

Regression of Epstein-Barr virus-associated lymphoproliferative disorders in patients with acquired immunodeficiency syndrome during therapy with foscarnet

Epstein-Barr virus (EBV)-associated lymphoproliferative disorders frequently develop in patients with acquired immunodeficiency syndrome (AIDS). The lymphoproliferative disorders are usually treated with a combination of cytotoxic drugs, and virustatic medication is thought to be ineffective. However, we report about two AIDS patients with EBV-associated lymphoproliferative disorders not responding to a standard chemotherapy, who achieved complete tumour regression after virustatic therapy with foscarnet.

Common and HIV-related diffuse large B-cell lymphomas differ in their immunoglobulin gene mutation pattern

HIV-infected patients are at high risk of developing diffuse large B-cell lymphomas (DLBCL). It is currently unclear whether these lymphomas represent Epstein-Barr virus (EBV)-driven lymphoproliferations that develop in the setting of immunodeficiency, or whether these tumours are more closely related to the DLBCL seen in the general population. To clarify this issue, 12 HIV-related DLBCL from 11 patients were analysed for the presence of clonally rearranged and somatically mutated immunoglobulin heavy chain (IgH) genes and their association with EBV was determined. Eleven of the 12 tumour samples displayed monoclonal rearrangements of the IgH genes, with or without a moderate number of somatic mutations in the CDRII and in the FWIII regions (average four mutations). One patient presented two successive lesions; whereas the initial tumour showed an oligoclonal IgH rearrangement, the lymphoma at relapse proved to harbour a monoclonal B-cell population. Ten of 12 tumour samples expressed the EBV encoded small RNAs (EBERs), and six of these EBV-positive cases displayed, in addition, an expression of the EBV encoded nuclear antigen 2 (EBNA-2). The results obtained from HIV-related DLBCL are at variance to those described for DLBCL occurring in the general population, since the latter contain significantly more somatic IgH mutations in the CDRII and in the FWIII regions and are only rarely associated with EBV. It is concluded from these findings that HIV-related DLBCL represent a distinct group of B-cell lymphomas, a significant fraction of which most likely originates from EBV-driven lymphoproliferations, and that half of the cases derive from pre-germinal centre B-cells.

A first-generation packaging cell line for Epstein-Barr virus-derived vectors

On the basis of the B lymphotropic Epstein-Barr virus (EBV), we have constructed a virus-free packaging cell line that allows encapsidation of plasmids into herpesvirus particles. This cell line harbors an EBV mutant whose packaging signals have been deleted. The gene vectors, which can encompass very large, contiguous pieces of foreign DNA, carry all cis-acting elements involved in amplification and encapsidation into virus-like particles as well as those essential for extrachromosomal maintenance in the recipient cell. Although this first-generation packaging cell line suffers from unwanted recombination between the helper virus genome and gene vector DNAs, this approach opens the way to delivery and stable maintenance of any transgene in human B cells.

Burkitt-like lymphomas in AIDS patients: characterization within a series of 103 human immunodeficiency virus-associated non-Hodgkin's lymphomas. Burkitt's Lymphoma Study Group

PURPOSE

Burkitt-like lymphoma (BLL) is a tumor with morphologic features intermediate between Burkitt's lymphoma (BL) and large-cell lymphoma, but its relationship with these lymphomas is currently unclear. We have therefore analyzed its characteristics within a large series of human immunodeficiency virus (HIV)-associated lymphomas.

MATERIALS AND METHODS

Clinical, histologic, immunophenotypic, and molecular analyses were performed on 103 patients with AIDS lymphomas.

RESULTS

Nineteen cases (18.4%) were identified as BLL. They were monoclonal B-cell proliferations, as evaluated by immunoglobulin (Ig) gene rearrangement analyses, and had rearrangement of the c-myc oncogene in 68% of cases but not the bcl-2 gene, in contrast to a previous study on non-HIV-associated BLL. This molecular pattern was therefore identical to that of typical BL, suggesting that they represented tumors of similar origin. However, some features could clearly differentiate BLL from BL and were similar to those seen in the diffuse large-cell immunoblastic lymphomas (DLC-IBL) group. These included a greater frequency of Epstein-Barr Virus (EBV) infection (79% v 48%, P = .04), an upregulation of CD39 (50% v 0%, P = .0007) and CD70 (75% v 15%, P = .003) activation antigens and of the CD11a/LFA-1 adhesion molecule (83% v30%, P = .05), and, finally, a lower CD4 count (mean, 119/microL v 270/microL, P = .04).

CONCLUSION

BLL is a frequent entity among AIDS lymphomas and should be considered as a morphologic variant of BL in the context of severe immunodepression that occurs in HIV-infected patients.

Activation of the Epstein-Barr virus transcription factor BZLF1 by 12-O-tetradecanoylphorbol-13-acetate-induced phosphorylation

BZLF1 is a member of the extended AP-1 family of transcription factors which binds to specific BZLF1 sequence motifs within early Epstein-Barr virus (EBV) promoters and to closely related AP-1 motifs. BZLF1's activity is regulated at the transcriptional level as well as through protein interactions and posttranslational modifications. Phorbol esters or immunoglobulin cross-linking both reactivate EBV from latently infected B cells via transactivation of BZLF1. We report here that the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) is capable of inducing BZLF1's activity even further. The induction occurs at the posttranscriptional level and depends on a single serine residue located in the DNA binding domain of BZLF1. This serine residue (S186) is phosphorylated by protein kinase C in vitro and in vivo after stimulation with TPA. Phosphorylation of S186 per se interferes with the DNA binding affinity of BZLF1 in vitro but is mandatory for TPA-induced increase in DNA binding of BZLF1, as shown in gel retardation assays and reconstruction experiments with cellular extracts. In transcriptional reporter assays, S186 is essential for the activation of BZLF1 by TPA. Presumably, a yet-to-be-identified cellular factor restores the DNA binding affinity and enhances the transcriptional activity of S186-phosphorylated BZLF1, which is required to induce the lytic phase of EBV's life cycle.

Lymphoproliferative lesions of the ocular adnexa. Analysis of 112 cases

OBJECTIVE

Lymphoproliferative lesions of the ocular adnexa were analyzed to examine (1) the suitability of the Revised European-American Lymphoma (REAL) classification for the subtyping of the lymphomas in these sites; (2) the predictive value of the REAL classification for the evolution of these tumors; and (3) the frequency and prognostic impact of tumor type, location, proliferation rate (Ki-67 index), p53, CD5 positivity and the presence of monoclonality within these tumors.

DESIGN

Retrospective review.

METHODS

The clinical, histomorphologic, immunohistochemical, and molecular biologic (polymerase chain reaction [PCR]) features of lymphoid proliferations of the ocular adnexa were studied. STUDY MATERIALS: The ocular adnexal lymphoproliferative lesions were located as follows: orbit in 52 patients (46%), conjunctiva in 32 patients (29%), eyelid in 23 patients (21%), and caruncle in 5 patients (4%).

RESULTS

Reactive lymphoid hyperplasia was diagnosed in 12 cases and lymphoma in 99 cases; 1 case remained indeterminate. The five main subtypes of lymphoma according to the REAL classification were extranodal marginal-zone B-cell lymphoma (64%), follicle center lymphoma (10%), diffuse large cell B-cell lymphoma (9%), plasmacytoma (6%), and lymphoplasmocytic lymphoma (5%). Age, gender, and anatomic localization of the lymphomas did not have prognostic significance during a follow-up period of 6 months to 16.5 years (mean, 3.3 years). Extent of disease at time of presentation was the most important clinical prognostic factor: advanced disease correlated with increased risk ratios of having persistent disease at the final follow-up and with lymphoma-related death (P < 0.001). Histomorphologic features and immunohistochemical markers positively correlating with disseminated disease at presentation, stage at final follow-up, and occurrence of lymphoma-related death included cytologic atypia (P < 0.001), MIB-1 proliferation rate (P < 0.001), and tumor cell p53 positivity (P < 0.001). The MIB-1 proliferation rates greater than 20% in extranodal marginal-zone B-cell lymphoma corresponded to at least stage II lymphoma (P < 0.05).

CONCLUSION

The REAL classification is suitable for the subdivision of the ocular adnexal lymphomas. The MIB-1 proliferation rate and p53 positivity may aid the prediction of disease stage and disease progression, whereas PCR can support the diagnosis and reduce the number of histologically indeterminate lesions.

Propagation and recovery of intact, infectious Epstein-Barr virus from prokaryotic to human cells

With current techniques, genetic alterations of herpesviruses are difficult to perform, mostly because of the large size of their genomes. To solve this problem, we have designed a system that allows the cloning of any gamma-herpesvirus in Escherichia coli onto an F factor-derived plasmid. Immortalized B cell lines were readily established with recombinant Epstein-Barr virus (EBV), demonstrating that the F factor-cloned EBV genome has all the characteristics of wild-type EBV. Because any genetic modification is possible in E. coli, this experimental approach opens the way to the genetic analysis of all EBV functions. Moreover, it is now feasible to generate attenuated EBV strains in vitro such that vaccine strains can be designed. Because we incorporated the genes for hygromycin resistance and green fluorescent protein onto the E. coli cloned EBV genome, the still open question of the EBV target cells other than B lymphocytes will be addressed.

Disappearance of the Epstein-Barr virus in a relapse of Hodgkin's disease

Hodgkin's disease (HD) is associated with the Epstein-Barr virus (EBV) in approximately half of cases. This is a report of a case of nodular sclerosing HD of the B-cell type that was associated with EBV in the initial manifestation, but was found to be EBV-negative in the relapse of the tumour. Both tumours displayed similar clinical, pathological, and immunohistochemical features. This finding implies that in a given individual EBV can be lost from malignant tumours and therefore shows that the EBV infection is not required to maintain neoplastic growth of HD tumour cells.

Plasmablastic lymphomas of the oral cavity: a new entity associated with the human immunodeficiency virus infection

We report here a series of 16 highly malignant diffuse large B-cell lymphomas of the oral cavity with unique immunohistologic features. Fifteen of these developed in human immunodeficiency virus-positive patients. All cases displayed morphologic features of diffuse large-cell lymphomas but strikingly differed from them in that they showed a minimal or absent expression of the leukocyte common antigen as well as of the B-cell antigen CD20. Instead, the tumor cells showed a constant reaction with the plasma cell characteristic antibody VS38c and a frequent reaction with the CD79a antibody. This, in conjunction with a variable expression of cytoplasmic Ig and a monoclonal rearrangement of the Ig heavy chain gene in all of the three tested cases confirmed the B-cell nature, the clonal origin, and the plasmacellular differentiation of these neoplasms. The majority of these tumors were negative for the BCL-6 protein, with the remaining cases showing only a partial and weak expression of this antigen. An association with the Epstein-Barr virus (EBV) was found in 9 of 15 tested cases showing abundant EBV-encoded nuclear RNA transcripts in the absence of EBNA-2. Five of the EBV-positive cases variably expressed LMP-1. We propose to name these tumors plasmablastic lymphomas, in accordance with their morphologic and immunohistologic features. Knowledge of this lymphoma entity is important to avoid confusion with nonlymphoid malignancies due to the lack of commonly used lymphoid markers.

Interleukin (IL)-10 and IL-6 are produced in vivo by non-Hodgkin's lymphoma cells and act as cooperative growth factors

The in vivo production of interleukin (IL)-10, IL-6, IL-2, and tumor necrosis factor (TNF)-alpha in tumor samples was investigated by immunohistochemistry in 54 non-Hodgkin's lymphomas (NHLs). Respectively, 55, 89, 23, and 29% of tumor samples were found positive for IL-10, IL-6, IL-2, and TNF-alpha expression by immunohistochemistry. Using reverse transcription-PCR, the mRNA of IL-10 and IL-6 were detectable in all samples tested and in 90 and 34% of the samples for TNF-alpha and IL-2, respectively. In 13 patients, fresh tumor tissue was available for B NHL cell purification with Dynabeads. IL-10, IL-6, IL-2, and TNF-alpha were detectable in the supernatant of 38, 100, 0, and 23% of purified tumor cell preparations (PTCPs), respectively. All patients with detectable IL-10 in culture had increased serum IL-10. IL-6 production by tumor cells and serum IL-6 levels were also found to be highly correlated (P < 0.0001). This suggests that tumor cells are a major source of serum IL-1O and IL-6 in these patients. Exogenous IL-10, IL-6, IL-2, and TNF-alpha significantly enhanced the [3H]thymidine uptake in 13 of 13 (100%), 5 of 13 (38%), 9 of 13 (69%), and 2 of 10 (20%) PTCPs costimulated with anti-CD40, respectively. IL-2, IL-6, and TNF-alpha synergized with IL-10 in 54, 23, and 30% of PTCPs. The combination of IL-10, IL-2, and IL-6 induced the maximal level of proliferation in 12 (92%) of 13 PTCPs. CD40 ligand mRNA expression was also detectable in vivo using reverse transcription-PCR in 28 of the 29 (97%) tumor samples tested, including 11 of those tested for [3H]thymidine incorporation. These results show that IL-1O, IL-6, IL-2, and TNF-alpha are produced in NHL tumors and may cooperate in vivo to increase NHL cell proliferation.

Complete nucleotide sequence of Ig V genes in three cases of Burkitt lymphoma associated with AIDS

To investigate the role of polyclonal stimulation and antigen driven selection in the pathogenesis of acquired immunodeficiency syndrome (AIDS) related lymphomas, we studied the variable region nucleotide sequence of heavy (VH) and light (VL) chains expressed by 3 Burkitt lymphomas (BL) associated with HIV infection. Two cases expressed the VH3-30P1 gene with 88.6% and 86.7% homology when compared to their germinal counterpart, whereas the VH4-18 was rearranged in the third one (89% identity). All these genes displayed high numbers of mutations (27, 22, 28 respectively), predominating in CDR regions. The encoded light chain genes determined for cases 1 and 2 expressed the same V kappa I-018 gene. These results indicate that: 1) Although, it is difficult to address the issue of VH usage based on the limited number of cases studied, Burkitt's lymphoma associated with AIDS may use a restricted repertoire of Ig genes. 2) Mutations and/or replacements predominated in CDR regions, which might suggest the occurrence of an antigen driven selection process, at least in some AIDS associated lymphomas. However, the high ratio of mutations observed in framework (FW) regions also favors the possibility that the antigen selection process is associated with polyclonal B cell stimulation.

Bcl6/Laz3 rearrangements in post-transplant lymphoproliferative disorders

Post-transplant lymphoproliferative disorders (PTLD) are well-known complications of iatrogenic immune deficiency and are thought to result from the proliferation of B cells infected by the Epstein-Barr virus (EBV). Some large cell lymphomas occurring in the general population carry a rearrangement of the Bcl6/Laz3 zinc-finger-encoding gene. 15 EBV-associated PTLD were tested for the presence of Bcl6/Laz3 rearrangements by Southern blot analysis using two specific probes (F370, F372). One out of 15 cases displayed a rearranged band independent of the germline one. In contrast, 10 lymphoblastoid cell lines and one lymphoblastoid cell line passaged in an SCID mouse carried only germline alleles of Bcl6/Laz3 after Southern blot hybridization. This indicates that genetic abnormalities may also play an important role in the development of some PTLD.

The expression of Epstein-Barr virus latent proteins is related to the pathological features of post-transplant lymphoproliferative disorders

Transplant recipients are at increased risk for the development of post-transplant lymphoproliferative disorders (PTLDs). PTLDs harbor genomes of the Epstein-Barr virus, a herpesvirus that immortalizes B cells in vitro. At least five viral proteins are required for immortalization. Two of them are particularly important. Latent membrane protein (LMP) has transforming activity in fibroblasts, and Epstein-Barr antigen (EBNA)2 transactivates the expression of numerous cellular and viral genes. To determine whether the expression of EBNA2 and LMP is related to the histological and clinical presentation of PTLD, we tested their expression in 14 Epstein-Barr virus-positive cases. Using monoclonal antibodies to EBNA2 and LMP on paraffin sections, we found an expression of both proteins in 2 of 3 polymorphic PTLD and in 7 of 8 cases of monomorphic, large cell PTLD, without plasmacytic differentiation. One polymorphic and one large cell PTLD expressed LMP only. LMP and EBNA2 were found particularly in immunoblasts. The number of positive cells was extremely variable in the different cases as well as within the same biopsy. Three cases of PTLD had morphological and phenotypical features of plasmacytomas and did not stain for EBNA2 or LMP. This suggests that the expression of EBNA2 and LMP is related to the differentiation stage of the infected cells and that other viral or cellular proteins may contribute to tumor growth.

Rat monoclonal antibodies differentiating between the Epstein-Barr virus nuclear antigens 2A (EBNA2A) and 2B (EBNA2B)

Rat monoclonal antibodies were produced against the C-terminus of Epstein-Barr virus nuclear antigens 2A (EBNA2A) and 2B (EBNA2B) expressed as bacterial trpE fusion proteins. The initial screening was performed using a soluble bacterial extract containing the fusion proteins. Positive hybridomas were confirmed by immunofluorescence on SF158 (Spodoptera frugiperda) insect cells infected with recombinant baculovirus (Autographa californica nuclear polyhedrosis virus) and expressing the complete EBNA2A or EBNA2B genes. We selected a panel of antibodies which reacted either with both antigens or specifically with EBNA2A or with EBNA2B. The antibodies were extensively characterized using immunoprecipitation, Western blotting, epitope mapping on synthesized peptide segments of EBNA2A, immunocytology, and immunohistology on both cryostat sections and paraffin sections of AIDS-associated primary central nervous system lymphomas.

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.

Post-transplant lymphoproliferative disorders with genetic abnormalities commonly found in malignant tumours

Post-transplant lymphoproliferative disorders (PTLD) are potentially fatal complications of organ transplants. Impairment of the immune system by immunosuppressive drugs is the assumed cause of PTLD. The Epstein-Barr virus (EBV) is detected in most of the PTLD studied and is considered as the main aetiological agent. The clinical course of PTLD patients remains unpredictable, some lymphoproliferations regress after discontinuation of the immunosuppressive treatment, others behave as true malignant tumours. The mechanism by which a viro-induced lymphoproliferation evolves to an autonomous tumour remains unclear, and little is known about the genetic changes that occur during this process. We report two cases of fatal EBV-associated PTLD in heart transplant recipients. Both tumours were monoclonal and carried numerous chromosomal abnormalities, including a classic t(8;14)(q24;q32) with rearrangement of the MYC proto-oncogene. One tumour demonstrated an amplification of the proto-oncogene N-MYC. The EBNA2 gene was not expressed in tumoral cells, suggesting that the chromosomal abnormalities contributed the function of EBNA2 in these cells. The morphology of the tumours indicated that the cases presented here were not Burkitt's lymphomas. These findings provide some clues with regard to the genetic changes which lead to a B-cell malignancy in some transplant patients.

Immunophenotypic and genotypic analysis of acquired immunodeficiency syndrome-related non-Hodgkin's lymphomas. Correlation with histologic features in 36 cases. French Study Group of Pathology for HIV-Associated Tumors

High-grade B-cell-type non-Hodgkin's lymphomas are observed in 5% to 8% of patients positive for the human immunodeficiency virus. Nearly all cases belong to one of the three major histologic types: centroblastic or large noncleaved cell, immunoblastic and Burkitt's lymphoma, or small noncleaved cell. Some cases that are polymorphic are termed high-grade B-cell, not otherwise specified (NOS). The authors determined the immunophenotype of each histologic category of acquired immunodeficiency syndrome (AIDS)-related non-Hodgkins' lymphoma and sought a relationship with the presence of the Epstein-Barr virus (EBV). B-cell differentiation antigens, activation marker expression (human leukocyte antigen-DR, CD10, CD19, CD20, CD21, CD22, CD23, CD25, CD30, CD38), and epithelial membrane antigen were analyzed. The clonality was determined by the detection of cytoplasmic immunoglobulin, surface immunoglobulin, and the analysis of joining region (JH) immunoglobulin gene configuration by Southern blot. Epstein-Barr virus was detected either by Southern blot analysis using BamHI W probe fragment or by in situ hybridization with EBV-encoded RNA transcripts-1 specific probe. The immunophenotypic and genotypic results were compared with the morphology results and with the presence or absence of EBV. Burkitt's lymphomas were associated with EBV in 50% of cases, were monoclonal, and expressed mostly immunoglobulin (Ig) MK, CD10, CD19, CD20, CD22, and CD38. This immunophenotypic profile closely resembled those of the centroblastic cases (large noncleaved cell), in which EBV was absent. Epstein-Barr virus was associated with 90% of immunoblastic cases, and only CD10, CD20, and CD38 were expressed. CD71 was expressed in all categories of non-Hodgkin's lymphoma, and CD21 and CD23 were rarely expressed. Two cases of immunoblastic lymphoma and one case of high-grade B-NOS were polyclonal regarding JH rearrangement, but EBV tested with 1.9-Kb Xhol fragment was clonal. No significant immunophenotypic changes were noted in relation to the presence of EBV. Such studies comparing morphology, immunophenotype, and genotype could help classify and better understand the pathogenesis of AIDS-related non-Hodgkin's lymphoma.

Breakpoints of Burkitt's lymphoma t(8;22) translocations map within a distance of 300 kb downstream of MYC

The variant translocation t(8;22) in Burkitt's lymphoma (BL) cells joins band q24 of chromosome 8 distal to the proto-oncogene MYC to the immunoglobulin lambda locus. The distribution of breakpoints on chromosome 8 of 11 cell lines with t(8;22) has been investigated by in situ fluorescence hybridization and pulsed-field gel electrophoresis. We show that these chromosomal breakpoints generally fall within a region of about 300 kb 3' of MYC and that at least 8 out of 11 affect the previously characterized transcriptional unit PVT1. Comparable results were obtained in earlier experiments analyzing the variant t(2;8). Recently, in a series of BL cells carrying t(8;14), breakpoints upstream of MYC have been described at a similar distance. Therefore, our results suggest that deregulation of MYC by the immunoglobulin loci can occur at a distance of up to about 350 kbp of MYC.

Epstein-Barr virus latent and replicative gene expression in post-transplant lymphoproliferative disorders and AIDS-related non-Hodgkin's lymphomas. French Study Group of Pathology for HIV-associated Tumors

In acquired immunodeficiency, B-cell proliferation is usually associated with Epstein-Barr virus (EBV), implying the impairment of the normal control of EBV and EBV-infected cells. It has been assumed that EBV infection is latent in lymphoproliferative disorders. In order to determine the type of latency and to investigate whether any lymphoproliferative disorders enter into the lytic cycle, we analyzed the expression of latent and replicative EBV genes in 9 post-transplant lymphoproliferative disorders (PTLD) and in 23 EBV-positive AIDS-related non-Hodgkin's lymphomas (AR-NHL). The PTLD cases were categorized into polyclonal or monoclonal polymorphic tumors and monoclonal monomorphic tumors. The AR-NHL cases included large-cell/immunoblastic (LC/IB) and Burkitt's lymphoma (BL) groups. We demonstrated that varying patterns of latent-viral-gene expression are exhibited showing the 3 forms of latency. Polymorphic PTLD and LC/IB AR-NHL frequently expressed type II or III latency, whereas monomorphic tumors and BL AR-NHL showed type I latency. It is noteworthy that 3 cases of BL AR-NHL expressed latency II form. Induction of lytic cycle highlighted by the expression of BZLF1 occurred in 55.5% of PTLD, 36% of LC/IB and 22% of BL AR-NHL. In contrast, late viral proteins indicating productive cycle were present in 22% of PTLD, 14% of LC/IB, and were absent in BL cases. These data suggest that the impairment of EBV control permits disruption of latency, but the initiation of the lytic cycle may not always lead to viral production.

Epstein-Barr virus-latent gene expression and tumor cell phenotype in acquired immunodeficiency syndrome-related non-Hodgkin's lymphoma. Correlation of lymphoma phenotype with three distinct patterns of viral latency

We investigated 49 acquired immunodeficiency syndrome-related lymphomas (ARLs) for Epstein-Barr virus (EBV) by Southern blotting and in situ hybridization and, in positive cases, used cryostat immunohistology to compare EBV-latent gene expression (EBV encoded small RNA-1 [EBER-1], EBV nuclear antigen-2 [EBNA-2], latent membrane protein-1 [LMP-1] and host cell immunophenotype (CD11a, CD18, CD54, CD58, CD21, CD23, CD30, CD39, CDw70, immunoglobulin) patterns with those reported in other EBV infections. EBV+ immunoblast-rich/large cell ARLs (n = 22) showed three patterns of latency: broad (EBER+EBNA-2+/LMP-1+; n = 9), reminiscent of a lymphoblastoid cell line phenotype; restricted (EBER+/EBNA-2-/LMP-1-; n = 6), similar to endemic Burkitt's lymphoma; and intermediate (EBER+/EBNA-2-/LMP-1+; n = 7), a pattern rarely described in vitro but seen in certain EBV-related malignancies. EBNA-2 expression was associated with extranodal lymphomas. EBV+ Burkitt-type ARLs (n = 11) usually showed the restricted latency pattern (n = 8), but some expressed the intermediate form (n = 3). Adhesion (CD54, CD58) and activation (CD30, CD39, CDw70) molecule expression varied with morphology (immunoblast-rich/large cell versus Burkitt-type), but was not independently correlated with EBV-positivity. CD30 and LMP-1 expression were associated. ARLs show heterogeneity regarding both the presence of EBV and latency pattern. Comparison of these phenotypically distinct lymphoma groups with known forms of EBV infection provides clues to their possible pathogenesis.

Mitogenicity of anti-Thy-1 monoclonal antibodies attributable to an Fc-dependent mechanism

We analyzed the mechanism by which certain anti-Thy-1 monoclonal antibodies (mAb) activate T cells directly without additional stimuli. Using a panel of rat anti-Thy-1 antibodies which included more than 30 IgG2c mAb, we found that only the IgG2c isotype was able to induce a strong proliferative response in both resting T cells and a T cell lymphoma, suggesting that this form of T cell activation is isotype restricted and might be a consequence of a unique physico-chemical property of the IgG2c heavy chain. Results from surface distribution studies of Thy-1 molecules, following specific interactions with anti-Thy-1 antibodies of different isotypes, again showed that only IgG2c mAb formed Thy-1 aggregates of high valence on the surface of a T cell lymphoma, and such clustering always evoked a biological response. This led us to propose that IgG2c mAb have the inherent tendency to self-associate, probably through homophilic Fc-Fc contacts, and that this feature renders anti-Thy-1 mAb mitogenic. To prove this, we set up cross-inhibition studies with randomly selected mitogenic (IgG2c) and nonmitogenic (IgG2b) anti-Thy-1 mAb. The results clearly demonstrated that IgG2c antibodies enhance their own binding, analogous to the new form of antibody binding that was recently demonstrated between murine IgG3 mAb and a multivalent antigen. Confirmation of this was also provided by IgG2c-derived F(ab')2 fragments, which were unable to cause proliferation. Furthermore, masking the Fc part of cell-bound IgG2c mAb with a monomeric and thus non-aggregating IgG-binding protein A-derived fragment cancelled their mitogenic ability. Finally, induction of T cell proliferation appeared to be independent of cross-linking via Fc gamma R. The results support a model in which noncovalent intermolecular homophilic contacts of the Fc regions of the IgG2c isotype bring about effective aggregation of Thy-1 molecules, thereby stimulating the mitotic apparatus of the cell.

[Lymphomas in immunocompromised hosts]

Congenital and acquired states of immunodeficiency are associated with an increased incidence of ill-defined lymphoproliferations. These are mainly B-cell, often extranodal, lymphoproliferations commonly associated with EBV. Their incidence is increasing with the rapid development of organ transplantation and spreading of the HIV infection. The association with EBV partly explains the pathogeny of these affections. This ubiquitous virus immortalizes B lymphocytes in vitro and is tumorigenic for new world primates. An EBV-specific cytotoxic T-cell memory prevents uncontrolled proliferation of infected B cells in normal subjects after the primary infection. The X-linked lymphoproliferative syndrome is a primary immunodeficiency characterized by an abnormal immune responsiveness to EBV, resulting in fatal infectious mononucleosis and malignant lymphoma. The severe immunosuppression present in transplanted patients allows EBV infected cells to proliferate, giving rise to a spectrum of lymphoproliferations. Reduction of immunosuppression alone is, in some cases, sufficient to produce tumor regression. The evolution of these affections is difficult to predict and requires a combined biological and clinical analysis, in order to evaluate the aggressivity of the tumor and the ability of the immune response of the host. HIV infected patients have an increased risk of developing Burkitt's lymphomas which are associated with EBV in 50% of the cases. Patients with AIDS at an advanced stage, present immunoblastic large cell lymphomas associated with EBV, similar to the post-transplant lymphomas. Lymphoproliferations in immunodeficiencies constitute a model for evaluation of the interaction between EBV and the immune system.

Latent Marek's disease virus can be activated from its chromosomally integrated state in herpesvirus-transformed lymphoma cells

Marek's disease virus (MDV), a lymphotropic herpesvirus, induces T-cell lymphomas in chicken, its natural host. The lymphoma cells are latently infected with MDV but the viral contribution to the transformed phenotype is not understood. To investigate the virus-cell interaction, we focused on the status of MDV in the transformed cells. By the use of highly sensitive fluorescent in situ hybridization with metaphase chromosomes, we found (i) MDV DNA to be randomly integrated at multiple sites in the chromosomes of primary lymphoma cells from chicken tissues; (ii) extrachromosomal, circular MDV genomes were absent and linear virion DNA was usually not detectable in the latently infected lymphoma cells; (iii) the pattern of integration sites revealed the clonal origin of the tumour cells; which (iv) was retained in in vitro established cell lines derived from primary lymphomas; (v) activation of the lytic phase of MDV's life cycle occurred in vitro suggesting that MDV can escape from its integrated status by an unknown mechanism.

Variable morphology of human immunodeficiency virus-associated lymphomas with c-myc rearrangements. The French Study Group of Pathology for Human Immunodeficiency Virus-Associated Tumors, I

Burkitt lymphoma (BL) and immunoblastic lymphoma (IL) are the most frequent lymphoid tumors encountered in human immunodeficiency virus (HIV)-infected patients. Tumors with a morphology intermediate between BL and IL, and the existence of Burkitt's type translocations in some IL cases makes the classification of these tumors sometimes unclear. We have studied 14 cases of BL and IL in HIV-seropositive individuals with regard to clonality, Epstein-Barr virus (EBV) association, and the presence of c-myc rearrangement. Of seven tumors with morphology of BL, all were monoclonal, six showed a c-myc rearrangement and four were associated with EBV. Five tumors with morphology of IL were associated with EBV and devoid of c-myc rearrangement. Three were polyclonal representing EBV-driven lymphoproliferations similar to those observed in transplant recipients. Two tumors, one with a morphology of IL and the other intermediate between IL and BL were monoclonal, associated with EBV, and harbored a c-myc rearrangement. We propose that these last two tumors represent cases of BL that have adopted an immunoblastic morphotype in the context of acquired immunodeficiency syndrome (AIDS), reflecting the morphologic evolution of Burkitt lymphoma cells observed in culture.

Episomal and integrated copies of Epstein-Barr virus coexist in Burkitt lymphoma cell lines

The Epstein-Barr virus genome is present in more than 95% of the African cases of Burkitt lymphoma. In this tumor, the viral genome is usually maintained in multiple episomal copies. Viral integration has been described only for Namalwa, a cell line lacking episomes. In this study, we have addressed the question of whether integrated and episomal copies can coexist in Burkitt lymphoma cells. Gel electrophoresis was used to demonstrate the presence of episomal as well as free linear DNA in three Burkitt lymphoma cell lines. The numbers of episomal copies per cell were estimated to be 5 to 10 in BL36 and BL137 cells and below 1 in BL60 cells, indicating that BL60 does not represent a homogeneous cell population. Fluorescence in situ hybridization was combined with chromosomal banding to study the association of the viral DNA with metaphase chromosomes. A symmetrical pattern of signals at both chromatids located at the same chromosomal sites in many if not all metaphases was taken as evidence for viral integration. In each of the three cell lines, one site of integration was identified: at chromosome 11p15 in BL36 cells, at chromosome 1p34 in BL137 cells, and at the site of a reciprocal t(11;19) translocation in BL60 cells. Integrated, episomal and linear copies of Epstein-Barr virus DNA thus coexist in Burkitt lymphoma cells. The biological significance of viral integration in Burkitt lymphoma cells remains to be elucidated.

Status of Marek's disease virus in established lymphoma cell lines: herpesvirus integration is common

Six cell lines derived from Marek's disease lymphomas of chickens and turkeys were investigated for the status of Marek's disease virus (MDV) DNA. In the transformed T- and B-cell lines, viral DNA could be detected by conventional Southern blot hybridization, by Gardella gel electrophoresis, and by in situ hybridization of metaphase and interphase chromosomes. Integration of viral DNA into the host cell chromosome was observed in all cell lines. Two to 12 integration sites of viral DNA could be detected in metaphase chromosome spreads. The integration sites were characteristic for the individual cell lines and were preferentially located at the telomers of large- and mid-sized chromosomes or on minichromosomes. In four of six cell lines, a minor population of latently infected cells supported the lytic cycle of MDV, giving rise to linear virion DNAs. In one of these cell lines, a third species of MDV DNA could be detected with properties reminiscent of covalently closed circular DNA. The finding that MDV integrates regularly into the genomes of latently infected cells is crucial to understanding the molecular biology of herpesvirus-induced tumors in the natural host.

Interleukin-6 production in high-grade B lymphomas: correlation with the presence of malignant immunoblasts in acquired immunodeficiency syndrome and in human immunodeficiency virus-seronegative patients

The mechanisms leading to malignant cell proliferation may differ between the different histologic forms of high-grade non-Hodgkin's lymphomas. To analyze the potential role of interleukin-6 (IL-6) as a growth factor for lymphomatous cells in these different forms, the in situ production of this cytokine was analyzed in lymphomatous samples taken from 24 patients, 18 of whom were human immunodeficiency virus (HIV) infected. Eleven Burkitt's lymphomas (BLs), seven diffuse large-cell lymphomas, and six immunoblastic lymphomas were studied. In situ hybridization experiments showed that the IL-6 gene was expressed in all tissues. The number of IL-6 gene-expressing cells was 7 times higher in the non-BLs than in the BLs, and it was 17 times higher than that of 14 control lymph nodes displaying a benign follicular hyperplasia. Analysis of individual cases indicated that the level of IL-6 gene expression was strongly correlated with the presence of immunoblasts within the malignant clone. In contrast, this level was not correlated with the presence of Epstein-Barr virus genome in the lymphoma or with the HIV status of patients. Immunohistochemical studies with an anti-IL-6 monoclonal antibody showed that IL-6 was produced in non-BLs, but not in BLs. In the former, IL-6 mainly originated from reactive, nonmalignant cells. Immunohistochemical analyses of non-BLs also showed that malignant cells produced the 80-Kd chain of the IL-6 receptor. Taken together, these results suggest that IL-6 may act as a growth factor in some forms of high-grade B lymphomas. The presence of immunoblasts may be an indicator of such forms.

Detection of Epstein-Barr virus genomes in AIDS related lymphomas: sensitivity and specificity of in situ hybridisation compared with Southern blotting

Eighteen cases of AIDS related, non-Hodgkin's lymphomas were examined for the presence of Epstein-Barr virus (EBV) genomes using in situ hybridisation with a 35S-labelled probe. The results were compared with those obtained independently by Southern blot analysis with a 32P-labelled probe of frozen tissue from the same tumours. Technically satisfactory results were obtained with both methods in 15 lymphomas. EBV DNA was detected in seven of 15 (47%) cases by in situ hybridisation and in eight of 15 (53%) cases by Southern blotting (including all the cases positive by in situ hybridisation). The results of EBV DNA detection by the two techniques were identical in 14 of 15 (93%) cases. In situ hybridisation gave no false positive results. This study shows that the sensitivity and specificity of in situ hybridisation for the detection of EBV genomes in AIDS related lymphomas approaches that of Southern blotting, even when using routinely processed archival, paraffin wax embedded material.