The LCR of EBV makes Burkitt's lymphoma endemic

First reported case: Uncommon presentation of Burkitt lymphoma as perineal ulceration in a young patient

INTRODUCTION AND IMPORTANCE

Burkitt lymphoma (BL) is an aggressive subtype of non-Hodgkin lymphoma with a predilection for pediatric patients, known for its rapid growth and MYC oncogene-associated chromosomal translocations.

CASE PRESENTATION

A 33-year-old male presented with a perineal ulcerated wound, initially misdiagnosed as a musculoskeletal injury. Imaging and histopathological analysis eventually confirmed BL, leading to the initiation of high-dose chemotherapy.

CLINICAL DISCUSSION

BL is characterized by its rapid growth, typically as masses in the abdomen or jaw. Nevertheless, atypical presentations can lead to diagnostic delays, underscoring the importance of considering BL even in the absence of classic symptoms. Swift recognition and accurate diagnosis are critical for initiating timely chemotherapy. Comprehensive clinical evaluation, advanced imaging, and histopathological analysis are pivotal in confirming the diagnosis.

CONCLUSION

This unique case of BL with a perineal mass presentation emphasizes the necessity of considering BL as a potential diagnosis in atypical cases, highlighting the importance of early recognition and appropriate therapeutic strategies. Healthcare professionals should be aware of the potential for unusual BL presentations.

Current Trends and Alternative Scenarios in EBV Research

Epstein-Barr virus (EBV) infection is associated with several distinct hematological and epithelial malignancies, e.g., Burkitt lymphoma, Hodgkin lymphoma, nasopharyngeal carcinoma, gastric carcinoma, and others. The association with several malignant tumors of local and worldwide distribution makes EBV one of the most important tumor viruses. Furthermore, because EBV can cause posttransplant lymphoproliferative disease, transplant medicine has to deal with EBV as a major pathogenic virus second only to cytomegalovirus. In this review, we summarize briefly the natural history of EBV infection and outline some of the recent advances in the pathogenesis of the major EBV-associated neoplasms. We present alternative scenarios and discuss them in the light of most recent experimental data. Emerging research areas including EBV-induced patho-epigenetic alterations in host cells and the putative role of exosome-mediated information transfer in disease development are also within the scope of this review. This book contains an in-depth description of a series of modern methodologies used in EBV research. In this introductory chapter, we thoroughly refer to the applications of these methods and demonstrate how they contributed to the understanding of EBV-host cell interactions. The data gathered using recent technological advancements in molecular biology and immunology as well as the application of sophisticated in vitro and in vivo experimental models certainly provided deep and novel insights into the pathogenetic mechanisms of EBV infection and EBV-associated tumorigenesis. Furthermore, the development of adoptive T cell immunotherapy has provided a novel approach to the therapy of viral disease in transplant medicine and hematology.

Epstein-Barr Virus: Clinical Diagnostics

The vast majority of the human adult population is infected with Epstein-Barr virus (EBV), and the majority of the EBV-infected individuals tolerates the infection well, without any further symptoms after primary infection. In cases of individuals which undergo primary infection in the form of an infectious mononucleosis, or which have undergone primary infection in their past, it is sometimes important to appraise symptomatic disease or differentiate infectious mononucleosis from other conditions. In these cases, serological methods, i.e., immunofluorescence, ELISA, or Western blot, are the methods of choice to come to an unequivocal diagnostic conclusion, while the detection and quantification of viral DNA through PCR plays a minor role.On the other hand, in a minority of the human population, EBV infection is associated or causally linked with autoimmune or malignant disease. Especially in the bone marrow or solid organ transplanted, or in otherwise severely immune-suppressed patients, prolonged EBV primary infection or EBV reactivation from latency may be a serious and life-threatening complication which needs to be diagnosed the faster the better, in order to take therapeutic steps in time. Determining the serostatus correctly is also important in these cases. However, the direct and quantitative detection of viral DNA are of importance for the diagnosis of serious EBV disease and its monitoring.In the following, we give an overview of diagnostic methods to accurately determine EBV serostatus and viral load. We evaluate the advantages and disadvantages of each method and report on the diagnostic significance of each and how to resolve diagnostic problems in case of uncertainties. For practical procedures, we refer to the detailed instruction manuals of the respective test kit manufacturers which have to be closely followed for reliable results.

Role of epigenetics in EBV regulation and pathogenesis

Epigenetic modifications of the viral and host cell genomes regularly occur in EBV-associated lymphomas and carcinomas. The cell type-dependent usage of latent EBV promoters is determined by the cellular epigenetic machinery. Viral oncoproteins interact with the very same epigenetic regulators and alter the cellular epigenotype and gene-expression pattern: there are common gene sets hypermethylated in both EBV-positive and EBV-negative neoplasms of different histological types. A group of hypermethylated promoters may represent, however, a unique EBV-associated epigenetic signature in EBV-positive gastric carcinomas. By contrast, EBV-immortalized B-lymphoblastoid cell lines are characterized by genome-wide demethylation and loss and rearrangement of heterochromatic histone marks. Early steps of EBV infection may also contribute to reprogramming of the cellular epigenome.

Molecular approaches towards characterization, monitoring and targeting of viral-associated hematological malignancies

Viral-associated malignancies usually arise in the setting of altered immunity or with declines in immune function associated with aging. The main culprits are the lymphotropic herpesvirus, including Epstein-Barr virus (EBV) and human herpesvirus-8, which are the focus of this review. Chronic persistent infection and viral reactivation are the main risk factors for development of herpesvirus-associated malignancies and have provided the rationale for intensive monitoring of viral loads in some clinical contexts. Quantitative detection of EBV levels in the post-transplant period and following treatment of EBV-associated malignancies now have a proven role in outcome prediction. Both T-cell immunotherapy and humoral immunotherapies directed against latent viral antigens represent promising interventional approaches to treatment of viral-associated malignancies.

Update on microbe-induced epigenetic changes: bacterial effectors and viral oncoproteins as epigenetic dysregulators

Pathoepigenetics is a new discipline describing how disturbances in epigenetic regulation alter the epigenotype and gene-expression pattern of human, animal or plant cells. Such ‘epigenetic reprogramming’ may play an important role in the initiation and progression of a wide variety of diseases. Infectious diseases also belong to this category: recent data demonstrated that microbial pathogens, including bacteria and viruses, are capable of dysregulating the epigenetic machinery of their host cell. The resulting heritable changes in host cell gene expression may favor the colonization, growth or spread of infectious pathogens. It may also facilitate the establishment of latency and malignant cell transformation. In this article, we review how bacterial epigenetic effectors and inflammatory processes elicited by bacteria alter the host cell epigenotype, and describe how oncoproteins encoded by human tumor viruses act as epigenetic dysregulators to alter the phenotype and behavior of host cells.

Epigenetic dysregulation of epstein-barr virus latency and development of autoimmune disease

Epstein-Barr virus (EBV) is ahumanherpesvirus thatpersists in the memory B-cells of the majority of the world population in a latent form. Primary EBV infection is asymptomatic or causes a self-limiting disease, infectious mononucleosis. Virus latency is associated with a wide variety of neoplasms whereof some occur in immune suppressed individuals. Virus production does not occur in strict latency. The expression of latent viral oncoproteins and nontranslated RNAs is under epigenetic control via DNA methylation and histone modifications that results either in a complete silencing of the EBV genome in memory B cells, or in a cell-type dependent usage of a couple of latency promoters in tumor cells, germinal center B cells and lymphoblastoid cells (LCL, transformed by EBV in vitro). Both, latent and lytic EBV proteins elicit a strong immune response. In immune suppressed and infectious mononucleosis patients, an increased viral load can be detected in the blood. Enhanced lytic replication may result in new infection- and transformation-events and thus is a risk factor both for malignant transformation and the development of autoimmune diseases. An increased viral load or a changed presentation of a subset of lytic or latent EBV proteins that cross-react with cellular antigens may trigger pathogenic processes through molecular mimicry that result in multiple sclerosis (MS), systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA).

Viral hit and run-oncogenesis: genetic and epigenetic scenarios

It is well documented that viral genomes either inserted into the cellular DNA or co-replicating with it in episomal form can be lost from neoplastic cells. Therefore, "hit and run"-mechanisms have been a topic of longstanding interest in tumor virology. The basic idea is that the transient acquisition of a complete or incomplete viral genome may be sufficient to induce malignant conversion of host cells in vivo, resulting in neoplastic development. After eliciting a heritable change in the gene expression pattern of the host cell (initiation), the genomes of tumor viruses may be completely lost, i.e. in a hit and run-scenario they are not necessary for the maintenance of the malignant state. The expression of viral oncoproteins and RNAs may interfere not only with regulators of cell proliferation, but also with DNA repair mechanisms. DNA recombinogenic activities induced by tumor viruses or activated by other mechanisms may contribute to the secondary loss of viral genomes from neoplastic cells. Viral oncoproteins can also cause epigenetic dysregulation, thereby reprogramming cellular gene expression in a heritable manner. Thus, we expect that epigenetic scenarios of viral hit and run-tumorigenesis may facilitate new, innovative experiments and clinical studies in spite of the fact that the regular presence of a suspected human tumor virus in an early phase of neoplastic development and its subsequent regular loss have not been demonstrated yet. We propose that virus-specific "epigenetic signatures", i.e. alterations of the host cell epigenome, especially altered DNA methylation patterns, may help to identify viral hit and run-oncogenic events, even after the complete loss of tumor viruses from neoplastic cells.

The importance of epigenetic alterations in the development of epstein-barr virus-related lymphomas

Epstein-Barr virus (EBV), a human gammaherpesvirus, is associated with a series of malignant tumors. These include lymphomas (Burkitt's lymphoma, Hodgkin's disease, T/NK-cell lymphoma, post-transplant lymphoproliferative disease, AIDS-associated lymphoma, X-linked lymphoproliferative syndrome), carcinomas (nasopharyngeal carcinoma, gastric carcinoma, carcinomas of major salivary glands, thymic carcinoma, mammary carcinoma) and a sarcoma (leiomyosarcoma). The latent EBV genomes persist in the tumor cells as circular episomes, co-replicating with the cellular DNA once per cell cycle. The expression of latent EBV genes is cell type specific due to the strict epigenetic control of their promoters. DNA methylation, histone modifications and binding of key cellular regulatory proteins contribute to the regulation of alternative promoters for transcripts encoding the nuclear antigens EBNA1 to 6 and affect the activity of promoters for transcripts encoding transmembrane proteins (LMP1, LMP2A, LMP2B). In addition to genes transcribed by RNA polymerase II, there are also two RNA polymerase III transcribed genes in the EBV genome (EBER 1 and 2). The 5' and internal regulatory sequences of EBER 1 and 2 transcription units are invariably unmethylated. The highly abundant EBER 1 and 2 RNAs are not translated to protein. Based on the cell type specific epigenetic marks associated with latent EBV genomes one can distinguish between viral epigenotypes that differ in transcriptional activity in spite of having an identical (or nearly identical) DNA sequence. Whereas latent EBV genomes are regularly targeted by epigenetic control mechanisms in different cell types, EBV encoded proteins may, in turn, affect the activity of a set of cellular promoters by interacting with the very same epigenetic regulatory machinery. There are EBNA1 binding sites in the human genome. Because high affinity binding of EBNA1 to its recognition sites is known to specify sites of DNA demethylation, we suggest that binding of EBNA1 to its cellular target sites may elicit local demethylation and contribute thereby to the activation of silent cellular promoters. EBNA2 interacts with histone acetyltransferases, and EBNALP (EBNA5) coactivates transcription by displacing histone deacetylase 4 from EBNA2-bound promoter sites. EBNA3C (EBNA6) seems to be associated both with histone acetylases and deacetylases, although in separate complexes. LMP1, a transmembrane protein involved in malignant transformation, can affect both alternative systems of epigenetic memory, DNA methylation and the Polycomb-trithorax group of protein complexes. In epithelial cells LMP1 can up-regulate DNA methyltransferases and, in Hodgkin lymphoma cells, induce the Polycomb group protein Bmi-1. In addition, LMP1 can also modulate cellular gene expression programs by affecting, via the NF-κB pathway, levels of cellular microRNAs miR-146a and miR-155. These interactions may result in epigenetic dysregulation and subsequent cellular dysfunctions that may manifest in or contribute to the development of pathological changes (e.g. initiation and progression of malignant neoplasms, autoimmune phenomena, immunodeficiency). Thus, Epstein-Barr virus, similarly to other viruses and certain bacteria, may induce pathological changes by epigenetic reprogramming of host cells. Elucidation of the epigenetic consequences of EBV-host interactions (within the framework of the emerging new field of patho-epigenetics) may have important implications for therapy and disease prevention, because epigenetic processes are reversible and continuous silencing of EBV genes contributing to patho-epigenetic changes may prevent disease development.

Epstein-Barr virus and its role in the pathogenesis of Burkitt's lymphoma: an unresolved issue

For several reasons Burkitt's lymphoma (BL) has become a paradigm in cancer research: for its particular geographical distribution, the presence of Epstein-Barr virus (EBV) in the cases in high incidence areas, and for the activation of the proto-oncogene c-myc by chromosomal translocation in one of the immunoglobulin gene loci. As c-MYC activates both, proliferation and apoptosis, at least two events have to cooperate in lymphomagenesis: activation of c-MYC and a shift in the balance from apoptosis towards survival. Antigenic and/or polyclonal stimulation of the B cell receptor, genetic instability imposed by activation induced deaminase (AID), as well as the viral gene products EBNA1 and several small non-coding non-polyadenylated RNAs are the main factors suspected to play an important role in the pathogenesis of BL. Despite intensive research, the role of the virus has remained largely elusive in the past decades, but the discovery of two viral microRNA clusters that are expressed in EBV associated tumors including BL has raised new hopes and expectations that EBV is going to reveal its mystery. This review focuses on the interplay between cellular and viral factors and puts special emphasis on mouse models and experimental cell culture systems that address these points.

Epstein-Barr virus and the pathogenesis of Burkitt's lymphoma: more questions than answers

Burkitt's lymphoma (BL) was first described as a clinical entity in children in Central Africa by Denis Burkitt in 1958. The particular epidemiological features of this tumor initiated the search for a virus as the causative agent and led to the discovery of Epstein-Barr virus (EBV) by Epstein and coworkers in 1964. It became apparent in the seventies and eighties that the tumor is not restricted to Central Africa, but occurs with lesser incidence all over the world (sporadic BL) and is also particularly frequent in HIV infected individuals, and that not all BL cases are associated with EBV: about 95% of the cases in Central Africa, 40 to 50% of the cases in HIV-infected individuals and 10 to 20% of the sporadic cases harbour the viral information and express at least one viral antigen (EBNA1) and a number of non-coding viral RNAs. In contrast, all BL cases regardless of their geographical origin exhibit one of three c-myc/Ig chromosomal translocations leading to the activation of the c-myc gene as a crucial event in the development of this disease. Although epidemiological evidence clearly points to a role of the virus in the African cases, the role of EBV in the pathogenesis of BL has remained largely elusive. This review summarizes current concepts and ideas how EBV might contribute to the development of BL in the light of the progress made in the last decade and discusses the problems of the experimental systems available to test such hypotheses.

Epigenetic dysregulation of the host cell genome in Epstein-Barr virus-associated neoplasia

Epstein-Barr virus (EBV), a human herpesvirus, is associated with a wide variety of malignant tumors. The expression of the latent viral RNAs is under strict, host-cell dependent transcriptional control. This results in an almost complete transcriptional silencing of the EBV genome in memory B-cells. In tumor cells, germinal center B-cells and lymphoblastoid cells, distinct viral latency promoters are active. Epigenetic mechanisms contribute to this strict control. In EBV-infected cells, epigenetic mechanisms also alter the expression of cellular genes, including tumor suppressor genes. In Nasopharyngeal Carcinoma, the hypermethylation of certain cellular promoters is attributed to the upregulation of DNA methyltransferases by the viral oncoprotein LMP1 (latent membrane protein 1) via JNK/AP1-signaling. The role of other viral latency products in the epigenetic dysregulation of the cellular genome remains to be established. Analysis of epigenetic alterations in EBV-associated neoplasms may result in a better understanding of their pathogenesis and may facilitate the development of new therapies.

Oral Burkitt's lymphoma--case report

Burkitt's lymphoma is a poorly differentiated rare and aggressive type of non-Hodgkin's lymphoma. This article reports the case of a male child aged seven years, who was examined at the Odontopediatric Clinic of the UFRN Dentistry Department. The patient presented a tumor in the premolar region of the mandible; teeth were mobile in this region. Radiology revealed a diffuse radioluscent area which was diagnosed histopathologically as Burkitt's lymphoma. The patient was treated with polychemotherapy; complete remission of the disease was attained.

Latency type-specific distribution of epigenetic marks at the alternative promoters Cp and Qp of Epstein-Barr virus

Transcripts for the Epstein-Barr virus (EBV)-encoded nuclear antigens are initiated at the alternative promoters Wp, Cp and Qp. Although the host cell-dependent activity of Cp is regulated by DNA methylation, Qp is unmethylated independently of its activity. Because histone modifications affect the chromatin structure, we compared the levels of diacetylated histone H3, tetraacetylated histone H4 and histone H3 dimethylated on lysine 4 (H3K4me2) at Cp and Qp, in well characterized cell lines representing the major EBV latency types. We found an activity-dependent histone code: acetylated histones marked active Cp, whereas active Qp was selectively enriched both in acetylated histones and H3K4me2. We concluded that active (but not silent) Cp and Qp are located to 'acetylation islands' in latent, episomal EBV genomes, similar to the active chromatin domains of the human genome.

Linfoma de Burkitt oral: relato de caso

O linfoma de Burkitt é um raro e agressivo tipo de linfoma não-Hodgkin pobremente diferenciado. O presente relato trata de uma criança do sexo masculino, com sete anos de idade, que foi examinada na Clínica de Odontopediatria do Departamento de Odontologia da UFRN, exibindo uma massa tumoral na região de pré-molares mandibulares com mobilidade dentária. O exame radiográfico revelou uma área radiolúcida difusa e o diagnóstico histopatológico foi de linfoma de Burkitt. O paciente foi tratado por poliquimioterapia e obteve completa remissão da patologia.

Epigenotypes of latent herpesvirus genomes

Epigenotypes are modified cellular or viral genotypes which differ in transcriptional activity in spite of having an identical (or nearly identical) DNA sequence. Restricted expression of latent, episomal herpesvirus genomes is also due to epigenetic modifications. There is no virus production (lytic viral replication, associated with the expression of all viral genes) in tight latency. In vitro experiments demonstrated that DNA methylation could influence the activity of latent (and/or crucial lytic) promoters of prototype strains belonging to the three herpesvirus subfamilies (alpha-, beta-, and gamma-herpesviruses). In vivo, however, DNA methylation is not a major regulator of herpes simplex virus type 1 (HSV-1, a human alpha-herpesvirus) latent gene expression in neurons of infected mice. In these cells, the promoter/enhancer region of latency-associated transcripts (LATs) is enriched with acetyl histone H3, suggesting that histone modifications may control HSV-1 latency in terminally differentiated, quiescent neurons. Epstein-Barr virus (EBV, a human gamma-herpesvirus) is associated with a series of neoplasms. Latent, episomal EBV genomes are subject to host cell-dependent epigenetic modifications (DNA methylation, binding of proteins and protein complexes, histone modifications). The distinct viral epigenotypes are associated with distinct EBV latency types, i.e., cell type-specific usage of latent EBV promoters controlling the expression of latent, growth transformation-associated EBV genes. The contribution of major epigenetic mechanisms to the regulation of latent EBV promoters is variable. DNA methylation contributes to silencing of Wp and Cp (alternative promoters for transcripts coding for the nuclear antigens EBNA 1-6) and LMP1p, LMP2Ap, and LMP2Bp (promoters for transcripts encoding transmembrane proteins). DNA methylation does not control, however, Qp (a promoter for EBNA1 transcripts only) in lymphoblastoid cell lines (LCLs), although in vitro methylated Qp-reporter gene constructs are silenced. The invariably unmethylated Qp is probably switched off by binding of a repressor protein in LCLs.

Persistent inflammation and hyperresponsiveness following viral rhinosinusitis

OBJECTIVES

To develop a murine model of viral rhinosinusitis.

STUDY DESIGN

Randomized, controlled, animal model.

METHODS

Mice were intranasally inoculated with Sendai virus (SeV) or ultraviolet (UV)-inactivated virus. On days 3 and 10 postinfection, nasal lavage fluid was obtained for viral culture. On days 4, 10, and 38 postinfection, sinus mucosa was harvested and analyzed by flow cytometry for CD3-, CD4-, CD8-, CD25-, CD11b-, CCR3-, and GR1-positive cells. Nasal hyperresponsiveness to histamine challenge was measured on days 8 and 36 postinoculation.

RESULTS

On day 3, viral cultures were positive from all SeV-inoculated mice but from none of the UV-inactivated mice (P<or=.0039). There was no growth of virus from either group on day 10. On day 4, flow cytometry on SeV-infected sinus cells showed a significant increase in macrophages (P<or=.03) and neutrophils (P<or=.02) compared with controls. This inflammation resolved by day 10. On day 38, mice inoculated with SeV had significantly more CD8+ (P<or=.044) and CD4+CD25+ (P<or=.017) cells than did controls. On day 8, there was a significant increase in both sneezing (P<or=.002) and nasal rubbing (P<or=.002) in the SeV-infected group to histamine challenge compared with controls. This difference continued to day 36.

CONCLUSIONS

Inoculation with SeV results in an acute infection that resolves spontaneously within 10 days. Infected mice develop a significant increase in T-suppressor and T-regulatory cells after resolution of the acute infection, which persists for at least 38 days. The persistence of these T cells is associated with hyperresponsiveness to histamine. This mouse model has some parallels to chronic rhinosinusitis after a viral infection in humans and should allow us to clarify the pathophysiology of this disease.

Regulation of Epstein-Barr virus latency type by the chromatin boundary factor CTCF

Epstein Barr virus (EBV) can establish distinct latency types with different growth-transforming properties. Type I latency and type III latency can be distinguished by the expression of EBNA2, which has been shown to be regulated, in part, by the EBNA1-dependent enhancer activity of the origin of replication (OriP). Here, we report that CTCF, a chromatin boundary factor with well-established enhancer-blocking activity, binds to EBV sequences between the OriP and the RBP-Jkappa response elements of the C promoter (Cp) and regulates transcription levels of EBNA2 mRNA. Using DNA affinity, electrophoretic mobility shift assay, DNase I footprinting, and chromatin immunoprecipitation (ChIP), we found that CTCF binds both in vitro and in vivo to the EBV genome between OriP and Cp, with an approximately 50-bp footprint at EBV coordinates 10515 to 10560. Deletion of this CTCF binding site in a recombinant EBV bacterial artificial chromosome (BAC) increased EBNA2 transcription by 3.5-fold compared to a wild-type EBV BAC. DNA affinity and ChIP showed more CTCF binding at this site in type I latency cell lines (MutuI and KemI) than in type III latency cell lines (LCL3456 and Raji). CTCF protein and mRNA expression levels were higher in type I than type III cell lines. Short interfering RNA depletion of CTCF in type I MutuI cells stimulated EBNA2 mRNA levels, while overexpression of CTCF in type III Raji cells inhibited EBNA2 mRNA levels. These results indicate that increased CTCF can repress EBNA2 transcription. We also show that c-MYC, as well as EBNA2, can stimulate CTCF mRNA levels, suggesting that CTCF levels may contribute to B-cell differentiation as well as EBV latency type determination.

Designing nonviral vectors for efficient gene transfer and long-term gene expression

Although the genetic therapy of human diseases has been conceptually possible for many years we still lack a vector system that allows safe and reproducible genetic modification of eukaryotic cells and ensures faithful long-term expression of transgenes. There is increasing agreement that vectors that are based exclusively on chromosomal elements, which replicate autonomously in human cells, could fulfill these criteria. The rational construction of such vectors is still hindered by our limited knowledge of the factors that regulate chromatin function in eukaryotic cells. This review sets out to summarize how our current knowledge of nuclear organization can be applied to the design of extrachromosomal gene expression vectors that can be used for human gene therapy. Within the past years a number of episomal nonviral constructs have been designed and their replication strategies, expression of transgenes, mitotic stability, and delivery strategies and the mechanisms required for their stable establishment will be discussed. To date, these nonviral vectors have not been used in clinical trials. Even so, many compelling arguments can be developed to support the view that nonviral vector systems will play a major role in future gene therapy protocols.

Epigenetic regulation of lymphoid specific gene sets

Coregulation of lymphoid-specific gene sets is achieved by a series of epigenetic mechanisms. Association with higher-order chromosomal structures (nuclear subcompartments repressing or favouring gene expression) and locus control regions affects recombination and transcription of clonotypic antigen receptors and expression of a series of other lymphoid-specific genes. Locus control regions can regulate DNA methylation patterns in their vicinity. They may induce tissue- and site-specific DNA demethylation and affect, thereby, accessibility to recombination-activating proteins, transcription factors, and enzymes involved in histone modifications. Both DNA methylation and the Polycomb group of proteins (PcG) function as alternative systems of epigenetic memory in lymphoid cells. Complexes of PcG proteins mark their target genes by covalent histone tail modifications and influence lymphoid development and rearrangement of IgH genes. Ectopic expression of protein noncoding microRNAs may affect the generation of B-lineage cells, too, by guiding effector complexes to sites of heterochromatin assembly. Coregulation of lymphoid and viral promoters is also possible. EBNA 2, a nuclear protein encoded by episomal Epstein-Barr virus genomes, binds to the cellular protein CBF1 (C promoter binding factor 1) and operates, thereby, a regulatory network to activate latent viral promoters and cellular promoters associated with CBF1 binding sites.Key words : lymphoid cells, coregulation of gene batteries, epigenetic regulation, nuclear subcompartment switch, locus control region, DNA methylation, Polycomb group of proteins, histone modifications, microRNA, Epstein-Barr virus, EBNA 2, regulatory network.