Epstein-Barr virus and Hodgkin's disease

HLA expression and HLA type associations in relation to EBV status in Hispanic Hodgkin lymphoma patients

A proportion of classical Hodgkin lymphomas harbor the Epstein Barr virus (EBV). We previously demonstrated that associations between Human Leukocyte Antigen (HLA) alleles and susceptibility to EBV+ classical Hodgkin lymphoma differ between European and Chinese populations. Data on Hispanic populations is missing. Here we examined the association between HLA type, tumor cell HLA expression and other characteristics in Hispanic Hodgkin lymphoma patients. Hispanic Hodgkin lymphoma patients diagnosed at the Los Angeles County-University of Southern California Medical Center from 2000–2012 were included (n = 65). Formalin-fixed paraffin-embedded tumor tissue was analyzed for EBV by in situ hybridization and for HLA class I and class II expression by immunohistochemistry. HLA typing was performed by HLA-A specific quantitative PCR of genomic DNA from tissue. Thirty patients (46%) had EBV+ tumors. Expression of HLA class I (p = 0.0006) was significantly associated with EBV+ tumor status in Hispanic patients, similar to Europeans and Chinese. A positive association between HLA class II expression and EBV+ tumor status, as present in large studies in Europeans, was not found (p = 0.06). The prevalences of the specific European HLA-A*01 risk and European HLA-A*02 protective types were not significantly associated with EBV+ tumors among these Hispanic patients, however numbers were too low to draw firm conclusions. The HLA-A*02:07 allele, that is associated with EBV+ Hodgkin lymphoma in Chinese, was absent. In conclusion, the association between EBV positivity in tumor cells and HLA class I expression appears to be consistent across different populations. Larger studies in Hispanics are needed to evaluate HLA allele susceptibility associations.

HLA-A*02 is associated with a reduced risk and HLA-A*01 with an increased risk of developing EBV+ Hodgkin lymphoma

Previous studies showed that the HLA class I region is associated with Epstein-Barr virus (EBV)-positive Hodgkin lymphoma (HL) and that HLA-A is the most likely candidate gene in this region. This suggests that antigenic presentation of EBV-derived peptides in the context of HLA-A is involved in the pathogenesis of EBV+ HL by precluding efficient immune responses. We genotyped exons 2 and 3, encoding the peptide-binding groove of HLA-A, for 32 single nucleotide polymorphisms in 70 patients with EBV+ HL, 31 patients with EBV- HL, and 59 control participants. HLA-A*01 was significantly overrepresented and HLA-A*02 was significantly underrepresented in patients with EBV+ HL versus controls and patients with EBV- HL. In addition, HLA-A*02 status was determined by immunohistochemistry or HLA-A*02-specific polymerase chain reaction (PCR) on 152 patients with EBV+ HL and 322 patients with EBV- HL. The percentage of HLA-A*02+ patients in the EBV+ HL group (35.5%) was significantly lower than in 6107 general control participants (53.0%) and the EBV- HL group (50.9%). Our results indicate that individuals carrying the HLA-A*02 allele have a reduced risk of developing EBV+ HL, while individuals carrying the HLA-A*01 allele have an increased risk. It is known that HLA-A*02 can present EBV-derived peptides and can evoke an effective immune response, which may explain the protective phenotype.

Characteristics of Epstein-Barr virus isolated from the malignant lymphomas in Korea

Epstein-Barr virus (EBV) is a common herpes virus linked to a variety of human neoplasms. In this study, the EBV detection was identified with the paraffin-embedded tissues from 62 non-Hodgkin's lymphomas, 20 Hodgkin's lymphomas, and 48 non-neoplastic tonsils, using PCR for EBNA-1 and EBER-1 mRNA in situ hybridization for EBER-1 mRNA. The isolates were analyzed for type 1/2, variants C/D and F/f, and LMP-1 30 bp deletion. EBV was isolated in 31 of 48 (66%) non-neoplastic tonsils, 24 of 42 (57%) B cell lymphomas, in 15 of 20 (75%) T cell lymphomas, and 17 of 20 (85%) Hodgkin's lymphomas. These viruses were classified as type 1 for 81% of non-neoplastic tonsils, 95% of B cell lymphomas, 93% of T cell lymphomas, and 73% of Hodgkin's diseases. Both type 1 and 2 viruses were isolated in one non-neoplastic tonsil and 3 Hodgkin's diseases. Type C virus was predominant in non-neoplastic tonsils (77%) and B cell lymphomas (75%), while type D virus was common in T cell lymphomas (71%) and Hodgkin's diseases (73%) (P < 0.05). Majority of the viruses detected in non-neoplastic tonsils (93%) and malignant lymphomas (91%) were "F" prototype. LMP-1 30 bp deletion was found in high frequency in both non-neoplastic tonsils (92%) and malignant lymphomas (86%). In conclusion, most of EBV found in Korea was type 1, and "DF" genotype was more frequent in T cell lymphomas and Hodgkin's diseases than in non-neoplastic tonsils and B cell lymphomas. LMP-1 30 bp deletion did not seem to be associated with malignant lymphomas.

Lymphoid cell infiltration into Epstein-Barr virus-positive nasopharyngeal carcinomas

OBJECTIVES

A pilot study was designed to analyze lymphoid cell infiltration in Epstein-Barr virus-positive (EBV+) nasopharyngeal carcinomas (NPCs) and to determine whether this pattern of infiltration is consistent with non-EBV+ head and neck carcinomas or with solid EBV+ tumors in other locations.

STUDY DESIGN

We performed a retrospective analysis of archived NPCs and oral cavity carcinomas.

METHODS

Immunohistochemical staining of the archive material for various markers (CD3, CD8, UCHL-1, S-100, and intercellular adhesion molecule) was performed. Polymerase chain reaction techniques to establish the presence of the EBV genome were used. Cells in different locations were counted under a light microscope by 2 of the authors.

RESULTS

The infiltration pattern of NPCs was different from that of oral cavity carcinomas. Stromal infiltration was significantly denser in oral cavity carcinomas. Tumor nest infiltration was more pronounced in NPCs. The pattern of infiltration was comparable with what has been described for other solid EBV+ tumors.

CONCLUSIONS

The immune response to NPCs is likely to be strongly influenced by the presence of the EBV genome. The pattern of infiltration is similar to that of other non-head and neck EBV+ solid tumors and different from that of EBV- head and neck carcinomas.

Hodgkin's disease and the Epstein-Barr virus

Hodgkin's disease is an unusual cancer because the malignant cells constitute only a minority of the total tumour mass and, as a consequence, the study of these cells has been a major challenge. Recently, the application of newer technologies, such as single cell polymerase chain reaction (PCR) and gene expression array analysis, to the study of Hodgkin's disease have yielded new insights into the pathogenesis of this tumour. In addition, the recognition that a proportion of Hodgkin's disease tumours harbour the Epstein-Barr virus (EBV) and that its genome is monoclonal in these tumours suggests that the virus contributes to the development of Hodgkin's disease in some cases. This review summarises current knowledge of the pathogenesis of Hodgkin's disease with particular emphasis on the association with EBV.

Involvement of two NF-kappa B binding elements in tumor necrosis factor alpha -, CD40-, and epstein-barr virus latent membrane protein 1-mediated induction of the cellular inhibitor of apoptosis protein 2 gene

The antiapoptotic function of NF-kappaB is believed to be mediated through the induction of antiapoptotic genes. Among the antiapoptotic genes, cellular inhibitor of apoptosis protein 2 (c-IAP2/HIAP-1/MIHC) is originally identified as a molecule recruited to the tumor necrosis factor (TNF) receptor complex, and its expression is preferentially up-regulated by TNF and other stimuli activating NF-kappaB. However, direct evidence of transcriptional regulation of NF-kappaB on the c-IAP2 gene is still missing. Here, we have cloned and characterized the promoter region required for NF-kappaB-dependent transcription of the c-IAP2 gene. Sequencing of a 3.5-kilobase fragment of the 5'-flanking region of the c-IAP2 gene has identified a TATA-like sequence and potential binding sites for nuclear factor of activated T cells, interferon regulatory factor 1, activator protein 1, glucocorticoid response element, and three putative NF-kappaB binding elements. Deletion and mutational analysis of the 5'-flanking region linked to the luciferase gene revealed that transcriptional activation by TNF or interleukin 1 is mediated cooperatively by two NF-kappaB binding sites. Electrophoretic mobility shift assays characterized that the two NF-kappaB sites can be recognized and bound by the NF-kappaB p50/p65 heterodimer. In addition, the transcription of c-IAP2 promoter was strongly up-regulated when CD40 or Epstein-Barr virus latent membrane protein 1 was overexpressed.

Haematopoietic cancer and medical history: a multicentre case control study

BACKGROUND

Viruses (such as Epstein-Barr virus) and pathological conditions (mainly involving immunosuppression) have been shown to increase the risk of haematolymphopoietic malignancies. Other associations (diabetes, tonsillectomy, autoimmune diseases) have been inconsistently reported.

METHODS

The association between different haematolymphopoietic malignancies (lymphomas, myelomas and leukaemias) and the previous medical history has been studied in a population-based case-control investigation conducted in Italy, based on face to face interviews to 2669 cases and 1718 population controls (refusal rates 10% and 19%, respectively). Controls were a random sample of the general population.

RESULTS

Previous findings were confirmed concerning the association between non-Hodgkin's lymphoma (NHL) and lupus erythematosus (odds ratio, OR=8.4; 95% CI 1. 6, 45), tuberculosis (OR=1.6; 1.05, 2.5) and hepatitis (1.8; 1.4, 2. 3). An association was found also between NHL and maternal (OR=2.8; 1.1, 6.9) or paternal tuberculosis (OR=1.7; 0.7, 3.9). Odds ratios of 4.0 (1.4, 11.8) and 4.4 (1.1, 6.6) were detected for the association between NHL and Hodgkin's disease, respectively, and previous infectious mononucleosis, but recall bias cannot be ruled out. No association was found with diabetes, tonsillectomy and adenoidectomy. An association with malaria at young age and "low grade" lymphatic malignancies is suggested. One interesting finding was the observation of four cases of poliomyelitis among NHL patients, one among Hodgkin's disease and one among myeloid leukaemia patients, compared with none among the controls (Fisher's exact test for NHL and Hodgkin's disease, p= 0.03, one tail).

CONCLUSIONS

Some of these findings are confirmatory of previous evidence. Other observations, such as the putative role of the polio virus and of malaria are new. A unifying theory on the mechanisms by which previous medical history may increase the risk of haematolymphopoietic malignancies is still lacking.

Tissue eosinophilia correlates strongly with poor prognosis in nodular sclerosing Hodgkin's disease, allowing for known prognostic factors

Although eosinophilic granulocytes are frequently observed in lymphatic tissue of Hodgkin's patients, no substantial data reveal the prognostic role, if any, of tissue eosinophilia. Thus, eosinophilia was analyzed histologically in 1511 diagnostic biopsy specimens of patients treated under protocol therapy of the German Hodgkin's Lymphoma Study Group between 1988 and 1994. Prominent eosinophilia was seen in 38% of cases, which differed among the histologic types of Hodgkin's disease (HD): none in lymphocyte predominant, 14% in lymphocyte rich classical, 40% in nodular sclerosis grade 1 (NS-1), 55% in nodular sclerosis grade 2, 43% in mixed cellularity (MC), and 54% in lymphocyte depleted. In a multivariate analysis, tissue eosinophilia proved to be the strongest prognostic factor for freedom from treatment failure (P &lt; .001) and overall survival (P &lt; .001) in a stage-stratified model. Among NS-1 patients, the effect was highly significant. In MC, no significant effect of eosinophilia on survival could be demonstrated. Eosinophils secrete CD30 ligand that is capable of binding to CD30 positive HD cells. The activation of TRAF2, followed by NF-kappaB, which occurs on CD30L/CD30 binding, may explain the neoplastic proliferation and apoptosis protection of HD cells. TRAF2 is also activated by EBV-LMP expression, which is detectable in the majority of MC but not NS cases. In addition to the possibility that eosinophils are only passive indicators for other unknown prognostic determinants, it may be concluded that the positive clinical outcome of eosinophilia-negative NS cases could be due to lower NF-kappaB activity.

Human herpesvirus type 7 in Hodgkin's disease

Several lines of evidence have pointed to the involvement of a viral agent in the pathogenesis of Hodgkin's disease (HD). Therefore we investigated the presence of human herpesvirus type 7 (HHV-7) in 53 cases of HD by polymerase chain reaction (PCR), DNA in situ hybridization (ISH) and immunohistochemistry. HHV-7 DNA was frequently detected (68% of the cases) in HD biopsies by PCR independently of the histological type, whereas only 32% (P<0.05) of positive cases were found in 19 reactive lymph nodes. However, by applying the quantitative PCR technique, the majority of the samples showed a low level of viral load. Moreover, ISH for HHV-7 DNA was positive in a low number of small T lymphocytes and consistently negative in Hodgkin and Reed-Sternberg (HRS) cells, which appeared negative for HHV-7 also at immunohistochemistry. These results indicate that the high frequency of HHV-7 infection in HD: (i) is probably non-productive, (ii) mainly involves small lymphocytes belonging to the T-lineage, and (iii) is probably due to the recruitment of non-malignant reactive cells in HD tissue.

Gene Expression by Single Reed-Sternberg Cells: Pathways of Apoptosis and Activation

Although Hodgkin's disease is highly responsive to treatments that cause apoptosis, it remains resistant to the physiological mechanisms intended to cause cell death. Presumably, the Reed-Sternberg cell defies endogenous apoptosis, persists, accumulates, and manifests the malignant disorder seen clinically. The Reed-Sternberg cell expresses several members of the tumor necrosis factor receptor superfamily. This family of receptors is involved in both activation and proliferation of cells, as well as either protection from or initiation of apoptosis in cells expressing these surface proteins. Signals from these receptors affect transcription. We reasoned that the activation state and resistance to apoptosis of Reed-Sternberg cells might be attributable to dysregulation of genes controling these processes. To determine gene expression by Reed-Sternberg cells, we developed a method of micromanipulation, global reverse transcription, and the reverse transcription-polymerase chain reaction and applied it to 51 single Reed-Sternberg cells and their variants from six cases of Hodgkin's disease. This report analyzes the gene expression of bcl-xs,bcl-xl, bax-α,bax-β, fadd, fas, fas ligand (fas L), ice,TNF-α, TNF-β,TNFR1, TNFR2, TRAF1,TRAF2, TRAF3, cIAP2, and tradd at the level of mRNA in the single Reed-Sternberg cells and their variants. The findings here suggest a molecular mechanism for the activated state and in vivo survival occurring in untreated Reed-Sternberg cells of Hodgkin's disease.

Gene Expression by Single Reed-Sternberg Cells: Pathways of Apoptosis and Activation

Although Hodgkin's disease is highly responsive to treatments that cause apoptosis, it remains resistant to the physiological mechanisms intended to cause cell death. Presumably, the Reed-Sternberg cell defies endogenous apoptosis, persists, accumulates, and manifests the malignant disorder seen clinically. The Reed-Sternberg cell expresses several members of the tumor necrosis factor receptor superfamily. This family of receptors is involved in both activation and proliferation of cells, as well as either protection from or initiation of apoptosis in cells expressing these surface proteins. Signals from these receptors affect transcription. We reasoned that the activation state and resistance to apoptosis of Reed-Sternberg cells might be attributable to dysregulation of genes controling these processes. To determine gene expression by Reed-Sternberg cells, we developed a method of micromanipulation, global reverse transcription, and the reverse transcription-polymerase chain reaction and applied it to 51 single Reed-Sternberg cells and their variants from six cases of Hodgkin's disease. This report analyzes the gene expression of bcl-xs,bcl-xl, bax-α,bax-β, fadd, fas, fas ligand (fas L), ice,TNF-α, TNF-β,TNFR1, TNFR2, TRAF1,TRAF2, TRAF3, cIAP2, and tradd at the level of mRNA in the single Reed-Sternberg cells and their variants. The findings here suggest a molecular mechanism for the activated state and in vivo survival occurring in untreated Reed-Sternberg cells of Hodgkin's disease.

The physiologic reservoir of Epstein-Barr virus does not map to upper aerodigestive tissues

The human Epstein-Barr herpesvirus (EBV) has distinct oncogenic potential, but with over 90% of the adult world population infected, malignancy is a rare outcome of carrier status. However, EBV's association with over half of Hodgkin's and non-Hodgkin's lymphomas as well as several solid tumors, notably nasopharyngeal carcinoma, makes EBV-linked malignancies one of the largest single cancer entities. EBV is a B-lymphotropic virus, well controlled by surveillant T cells in immunocompetent hosts. To determine the presence and site of principal virus reservoirs is a likely prerequisite for understanding the etiology of EBV-associated tumors. Its near 100% association with nasopharyngeal carcinoma led to postulates that the upper aerodigestive tract tissue may be common sites of persistent latent or low-grade replicating infection. Using a protocol designed to avoid viral crosscontamination, the authors employed polymerase chain reaction to detect genomic EBV DNA sequences in 231 biopsies from different mucosal sites in the upper aerodigestive tract, as well as from salivary gland tissue and neck nodes in individuals not suspected to have EBV-related malignancy. Only two samples, one from oral cavity mucosa and one from parotid gland tissue, were positive for EBV. The observation that oropharyngeal tissue is not the principal EBV reservoir has mechanistic implications for the development of EBV-positive tumors in that locale.

Pathophysiology of Hodgkin's disease: functional and molecular aspects

Hodgkin's disease (HD) is characterized by the presence of the typical, clonal malignant Hodgkin and Reed-Sternberg (H-RS) cells in a hyperplastic background of normal reactive lymphocytes, plasma cells, histiocytes, neutrophils, eosinophils and stromal cells. The neoplastic nature of HD is based on aggressive clinical progression, presence of the proliferating and atypical H-RS cells, aneuploidy and cellular clonality. Immunophenotypical studies have demonstrated frequent expression of lymphoid "activation markers' including CD15, CD25, CD30, CD40, CD54, CD70, CD71, CD80, CD86 and MHC class II and less frequent expression of T- or B-cell-associated antigens by the neoplastic H-RS cells. The clonality of H-RS cells is demonstrated by clonal EBV integration, clonal cytogenetic abnormalities including p53 mutations and clonal immunoglobulin rearrangements in some HD cases. There is involvement of diverse molecules with oncogenic potential, including presence of viruses (Epstein-Barr virus and human herpes virus-6) and/or oncogenes/tumour suppressor genes (bcl-2/bcl-x, p53/MDM-2, c-myc, c-fms, N-ras, lck). The histopathological presentation and characteristic clinical features of HD correlate with an unbalanced production of multiple cytokines and define HD as a tumour of cytokine-producing cells. The proportion of malignant H-RS cells to reactive cellular components and fibrosis is dependent on the production of particular cytokines and allows subtyping of HD cases. The combined use of immunohistochemical, biochemical and molecular techniques has thus allowed recognition that HD represents more than one clinico-pathological entity with different types of H-RS cells. The defined mechanism for the biological nature, origin and oncogenesis of H-RS cells remains not fully understood, but is susceptible to further analysis using modern technology.

Determination of the number of Epstein-Barr virus genomes in whole blood and red cell concentrates

The risk of Epstein-Barr virus (EBV) infection after blood transfusion has been controversially discussed. Little is known about EBV transmission via buffy-coat-depleted red cell concentrates (RCC). In this study, we determined the number of EBV genomes in RCC of EBV-seropositive donors in comparison to whole blood. RCC were prepared from whole blood donations by using the 'top and bottom system'. Leucocyte content was significantly reduced in RCC in comparison to whole blood (0.47 x 10(9) vs. 2.3 x 10(9) per unit; P < 0.001). As B cells are expected to harbour EBV genomes, we analysed the number of B lymphocytes in both types of blood products. There was a significant reduction of B cell content from a median value of 90 x 10(6) in whole blood to 0.2 x 10(6) in RCCs (P < 0.001). The number of EBV genomes was estimated at a median value of seven from 10(6) B cells in the peripheral blood of healthy, EBV-seropositive blood donors by means of a polymerase chain reaction (PCR) assay. By calculation, one unit of RCC may contain an average of one to two EBV genomes, in contrast to a whole blood unit, which is likely to harbour an average of 600 to 700 EBV genomes. It is concluded that the use of leucocyte depletion systems significantly reduces the number of EBV genomes in erythrocyte concentrates. Thus, leucocyte reduced blood products appear to minimize the risk of EBV infection.

Characteristics of viral protein expression by Epstein-Barr virus-infected B cells in peripheral blood of patients with infectious mononucleosis

The frequency of Epstein-Barr virus (EBV) antigen-positive B cells in the peripheral blood of patients with infectious mononucleosis compared with that for latently EBV-infected individuals was examined by immunocytochemistry. B cells positive for Epstein-Barr nuclear antigen (EBNA) 1, EBNA2, and latent membrane protein were frequently found in all peripheral B lymphocyte preparations from 25 patients suffering for 3 to 28 days from infectious mononucleosis by using monoclonal antibodies and the alkaline phosphatase anti-alkaline technique. There was a significant decrease in the number of positive B cells during the course of disease. EBNA1-positive B cells were detected in 0.01 to 2.5% of total B cells (median, 0.8%), EBNA2-positive B cells were detected in 0.01 to 4.5% of total B cells (median, 0.9%), and latent membrane protein-positive B cells were detected in 0.01 to 1.8% of total B cells (median, 0.5%), depending on the duration of clinical signs. In contrast, we did not find any EBNA1- or EBNA2-positive B cells in 2 x 10(6) peripheral blood B lymphocytes of 10 latently EBV-infected individuals, whereas aliquots of the same cell preparations were EBV DNA positive by a PCR assay. Therefore, it appears to be possible to detect infectious mononucleosis by immunocytochemical determination of latent EBV products, which might be of relevance for the diagnosis of EBV reactivations in immunosuppressed patients.

Biopathologic features of Hodgkin's disease

The neoplastic nature of Hodgkin's disease (HD) is suggested by several lines of evidence, including aggressive clinical course, presence of proliferating atypical cells morphologically recognized as Hodgkin's and Reed-Sternberg cells (H-RS), aneuploidy, and, in the minority of cases, clonality. Nevertheless, the etiopathogenesis of HD still remains elusive, and probably diverse. This uncertainty is partly due to the peculiar histology of HD lesions, characterised by the paucity of the putative neoplastic cell component, i.e. H-RS cells, admixed to a variety of reactive cells which prevent an exhaustive investigation at molecular level. Nevertheless, the possible involvement of different molecules with oncogenic potential has been recently suggested on the basis of immunohistological and molecular biology studies. These include oncogenes such as bcl-2 and MDM2 and anti-oncogenes such as p53. In addition, a large amount of data has accumulated on the possible role of EBV infection in HD. The colonization of lymphoid tissues by immortalized H-RS cells can account for the derangement of cytokine networks leading to microenvironmental and systemic abnormalities. In addition, a variety of soluble receptors (sIL-2R, sCD30, sTNF-R), and adhesion molecules (sICAM-1) are abnormally produced at sites of disease involvement. Some of these molecules still retain the ability to bind their ligands and can potentially contribute to the derangement of immune mechanisms observed in HD. Many of these soluble molecules can also be found in the patient's sera providing new potential prognostic and follow-up parameters in HD patients. The comparative analysis of the same molecules within the tissue, using immunohistochemistry, and in the blood, using immunochemical assays, appears as a promising informative approach.

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

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