Defective activity of Epstein-Barr virus (EBV) specific cytotoxic T lymphocytes in children with chronic active EBV infection and in their parents

Clinical significance of anti-Epstein-Barr virus antibodies in systemic chronic active Epstein-Barr virus disease

Systemic chronic active Epstein-Barr virus disease (sCAEBV) is a rare and fatal neoplasm, involving clonally proliferating Epstein-Barr virus (EBV)-infected T cells or natural killer cells. Patients with sCAEBV have abnormal titers of anti-EBV antibodies in their peripheral blood, but their significance is unknown. We retrospectively investigated titers and their relationship with the clinical features of sCAEBV using the data collected by the Japanese nationwide survey. Eighty-four patients with sCAEBV were analyzed. The anti-EBV nuclear antigen (EBNA) antibody, targeting EBNA-expressing EBV-positive cells, was found in 87.5% of children (<15 years old), 73.7% of adolescents and young adults (15-39 years old), and 100% of adults (≥40 years old). Anti-EBNA antibody titers were significantly lower and anti-VCA-IgG antibody titers significantly higher in patients with sCAEBV than those in healthy controls (p < 0.0001). Patients with high anti-VCA-IgG and anti-early antigen-IgG antibody (antibodies against the viral particles) levels had significantly better 3-year overall survival rates than those with low titers, suggesting that patients with sCAEBV have a reduced immune response to EBV-infected cells.

Updated guidelines for chronic active Epstein-Barr virus disease

Chronic active Epstein-Barr virus disease (CAEBV), formerly named chronic active Epstein-Barr virus infection, is characterized by systemic inflammation and clonal proliferation of Epstein-Barr virus (EBV)-infected T or NK cells. As CAEBV is a potentially life-threatening illness, appropriate diagnosis and therapeutic interventions are necessary for favorable clinical outcomes. Substantial evidence regarding the pathogenesis and treatment of CAEBV has been accumulated since previous guidelines for the diagnosis of CAEBV were proposed. To reflect this evidence, we updated the guidelines for the diagnosis and treatment of CAEBV to improve clinical management of the disease. The details of the updated guidelines are presented in this report. Diagnosis of CAEBV now requires confirmation of a high copy number of EBV genome and EBV-infected T or NK cells. An EBV DNA load ≥ 10,000 IU/mL in whole blood is proposed as the diagnostic cutoff value for CAEBV in this updated guideline. A standard treatment approach for CAEBV has not been established, and hematopoietic stem cell transplantation (HSCT) is considered the only curative treatment. Chemotherapy can be administered to control disease activity before HSCT.

Characterizing EBV-associated lymphoproliferative diseases and the role of myeloid-derived suppressor cells

Chronic active Epstein-Barr virus (CAEBV) typically presents as persistent infectious mononucleosis-like disease and/or hemophagocytic lymphohistocytosis (HLH), reflecting ectopic Epstein-Barr virus (EBV) infection and lymphoproliferation of T and/or NK cells. Clinical behavior ranges from indolent, stable disease through to rapidly progressive, life-threatening disease. Although it is thought the chronicity and/or progression reflect an escape from immune control, very little is known about the phenotype and function of the infected cells vs coresident noninfected population, nor about the mechanisms that could underpin their evasion of host immune surveillance. To investigate these questions, we developed a multicolor flow cytometry technique combining phenotypic and functional marker staining with in situ hybridization for the EBV-encoded RNAs (EBERs) expressed in every infected cell. This allows the identification, phenotyping, and functional comparison of infected (EBERPOS) and noninfected (EBERNEG) lymphocyte subset(s) in patients' blood samples ex vivo. We have characterized CAEBV and HLH cases with monoclonal populations of discrete EBV-activated T-cell subsets, in some cases accompanied by EBV-activated NK-cell subsets, with longitudinal data on the infected cells' progression despite standard steroid-based therapy. Given that cytotoxic CD8+ T cells with relevant EBV antigen specificity were detectable in the blood of the best studied patient, we searched for means whereby host surveillance might be impaired. This revealed a unique feature in almost every patient with CAEBV studied: the presence of large numbers of myeloid-derived suppressor cells that exhibited robust inhibition of T-cell growth. We suggest that their influence is likely to explain the host's failure to contain EBV-positive T/NK-cell proliferation.

Chronic Active Epstein-Barr Virus Infection: Is It Immunodeficiency, Malignancy, or Both?

Simple Summary

Chronic active Epstein–Barr virus (EBV) infection (CAEBV) is a rare syndrome of unknown etiology characterized by prolonged infectious mononucleosis-like symptoms and proliferation of EBV-infected T and/or natural killer cells. CAEBV has been primarily reported in East Asia and Latin America, suggesting a genetic predisposition in its pathogenesis. The clinical course of CAEBV is heterogeneous ranging from an indolent and occasionally self-limiting disease to an aggressive and fatal condition, but its prognosis is generally poor. This heterogeneous clinical picture does not suggest a simple etiology for the syndrome. Clinicopathological investigations of CAEBV suggest that it has aspects of both malignant neoplasm and immunodeficiency. This article summarizes the latest findings on CAEBV and discusses critical unsolved questions regarding its pathogenesis and disease concept.

Abstract

Chronic active Epstein–Barr virus (EBV) infection (CAEBV) is a rare syndrome characterized by prolonged infectious mononucleosis-like symptoms and elevated peripheral blood EBV DNA load in apparently immunocompetent persons. CAEBV has been primarily reported in East Asia and Latin America, suggesting a genetic predisposition in its pathogenesis. In most cases of CAEBV, EBV induces proliferation of its unusual host cells, T or natural killer (NK) cells. The clinical course of CAEBV is heterogeneous; some patients show an indolent course, remaining in a stable condition for years, whereas others show an aggressive course with a fatal outcome due to hemophagocytic lymphohistiocytosis, multiple organ failure, or progression to leukemia/lymphoma. The pathogenesis of CAEBV is unclear and clinicopathological investigations suggest that it has aspects of both malignant neoplasm and immunodeficiency. Recent genetic analyses of both viral and host genomes in CAEBV patients have led to discoveries that are improving our understanding of the nature of this syndrome. This article summarizes the latest findings on CAEBV and discusses critical unsolved questions regarding its pathogenesis and disease concept.

How I treat T-cell chronic active Epstein-Barr virus disease

T-cell chronic active Epstein-Barr virus (CAEBV) is a rare disease in which EBV is present predominantly in T cells that infiltrate the tissues; patients have high levels of EBV in the blood. If untreated, patients often develop liver failure, hemophagocytic lymphohistiocytosis, coronary artery aneurysms, EBV infiltrating T cells impairing organ function, or T-cell lymphomas refractory to treatment. At present, hematopoietic stem-cell transplantation is the only curative therapy, and it is critical to make a proper diagnosis and initiate transplantation before the disease progresses to an irreversible stage. Specific medications such as high-dose systemic corticosteroids or ganciclovir combined with either histone deacetylase inhibitors or bortezomib may temporarily reduce systemic toxicity associated with T-cell CAEBV and allow the patient time to receive a transplant. Relapses of the disease after transplantation have also occurred, and the use of donor-derived virus-specific T cells may help to treat these relapses.

Chronic Active Epstein-Barr Virus Disease

Chronic active Epstein–Barr virus (CAEBV) disease is a rare disorder in which persons are unable to control infection with the virus. The disease is progressive with markedly elevated levels of EBV DNA in the blood and infiltration of organs by EBV-positive lymphocytes. Patients often present with fever, lymphadenopathy, splenomegaly, EBV hepatitis, or pancytopenia. Over time, these patients develop progressive immunodeficiency and if not treated, succumb to opportunistic infections, hemophagocytosis, multiorgan failure, or EBV-positive lymphomas. Patients with CAEBV in the United States most often present with disease involving B or T cells, while in Asia, the disease usually involves T or NK cells. The only proven effective treatment for the disease is hematopoietic stem cell transplantation. Current studies to find a cause of this disease focus on immune defects and genetic abnormalities associated with the disease.

Epstein-Barr virus-associated lymphomas

Epstein-Barr virus (EBV), originally discovered through its association with Burkitt lymphoma, is now aetiologically linked to a remarkably wide range of lymphoproliferative lesions and malignant lymphomas of B-, T- and NK-cell origin. Some occur as rare accidents of virus persistence in the B lymphoid system, while others arise as a result of viral entry into unnatural target cells. The early finding that EBV is a potent B-cell growth transforming agent hinted at a simple oncogenic mechanism by which this virus could promote lymphomagenesis. In reality, the pathogenesis of EBV-associated lymphomas involves a complex interplay between different patterns of viral gene expression and cellular genetic changes. Here we review recent developments in our understanding of EBV-associated lymphomagenesis in both the immunocompetent and immunocompromised host.This article is part of the themed issue 'Human oncogenic viruses'.

The Putative Role of Viruses, Bacteria, and Chronic Fungal Biotoxin Exposure in the Genesis of Intractable Fatigue Accompanied by Cognitive and Physical Disability

Patients who present with severe intractable apparently idiopathic fatigue accompanied by profound physical and or cognitive disability present a significant therapeutic challenge. The effect of psychological counseling is limited, with significant but very slight improvements in psychometric measures of fatigue and disability but no improvement on scientific measures of physical impairment compared to controls. Similarly, exercise regimes either produce significant, but practically unimportant, benefit or provoke symptom exacerbation. Many such patients are afforded the exclusionary, non-specific diagnosis of chronic fatigue syndrome if rudimentary testing fails to discover the cause of their symptoms. More sophisticated investigations often reveal the presence of a range of pathogens capable of establishing life-long infections with sophisticated immune evasion strategies, including Parvoviruses, HHV6, variants of Epstein-Barr, Cytomegalovirus, Mycoplasma, and Borrelia burgdorferi. Other patients have a history of chronic fungal or other biotoxin exposure. Herein, we explain the epigenetic factors that may render such individuals susceptible to the chronic pathology induced by such agents, how such agents induce pathology, and, indeed, how such pathology can persist and even amplify even when infections have cleared or when biotoxin exposure has ceased. The presence of active, reactivated, or even latent Herpes virus could be a potential source of intractable fatigue accompanied by profound physical and or cognitive disability in some patients, and the same may be true of persistent Parvovirus B12 and mycoplasma infection. A history of chronic mold exposure is a feasible explanation for such symptoms, as is the presence of B. burgdorferi. The complex tropism, life cycles, genetic variability, and low titer of many of these pathogens makes their detection in blood a challenge. Examination of lymphoid tissue or CSF in such circumstances may be warranted.

Current research on chronic active Epstein-Barr virus infection in Japan

Epstein-Barr virus (EBV) infection is usually asymptomatic and persists lifelong. Although EBV-infected B cells have the potential for unlimited proliferation, they are effectively removed by the virus-specific cytotoxic T cells, and EBV-associated lymphoproliferative disease develops only in immunocompromised hosts. Rarely, however, individuals without apparent immunodeficiency develop chronic EBV infection with persistent infectious mononucleosis-like symptoms. These patients have high EBV-DNA load in the peripheral blood and systemic clonal expansion of EBV-infected T cells or natural killer (NK) cells. Their prognosis is poor with life-threatening complications including hemophagocytic lymphohistiocytosis, organ failure, and malignant lymphomas. The term "chronic active EBV infection" (CAEBV) is now generally used for this disease. The geographical distribution of CAEBV is markedly uneven and most cases have been reported from Japan and other East Asian countries. Here we summarize the current understanding of CAEBV and describe the recent progress of CAEBV research in Japan.

Primary immunodeficiencies predisposed to Epstein-Barr virus-driven haematological diseases

Epstein-Barr virus (EBV), a ubiquitous human herpesvirus, maintains lifelong subclinical persistent infections in humans. In the circulation, EBV primarily infects the B cells, and protective immunity is mediated by EBV-specific cytotoxic T cells (CTLs) and natural killer (NK) cells. However, EBV has been linked to several devastating diseases, such as haemophagocytic lymphohistiocytosis (HLH) and lymphoproliferative diseases in the immunocompromised host. Some types of primary immunodeficiencies (PIDs) are characterized by the development of EBV-associated complications as their predominant clinical feature. The study of such genetic diseases presents an ideal opportunity for a better understanding of the biology of the immune responses against EBV. Here, we summarize the range of PIDs that are predisposed to EBV-associated haematological diseases, describing their clinical picture and pathogenetic mechanisms.

[Chronic active Epstein-Barr virus infection]

The ubiquitous Epstein-Barr virus (EBV), which establishes latency after primary infection, does not cause any symptomatic diseases as long as cellular immunity is intact. In apparently immunocompetent individuals, a chronic infection can develop, and this has been called as chronic active EBV infection (CAEBV). CAEBV is characterized by chronic or recurrent infectious mononucleosis-like symptoms, such as fever, extensive lymphadenopathy, and, hepatosplenomegaly. This disease is rare but severe with high morbidity and mortality. Recently, its pathophysiology is not an infection but a clonal expansion of EBV-infected T or natural killer NK cells. In this review, I discuss our current understanding of the pathogenesis of CAEBV and summarize its clinical features, therapies, and prognosis.

Characterization and treatment of chronic active Epstein-Barr virus disease: a 28-year experience in the United States

Chronic active EBV disease (CAEBV) is a lymphoproliferative disorder characterized by markedly elevated levels of antibody to EBV or EBV DNA in the blood and EBV RNA or protein in lymphocytes in tissues. We present our experience with CAEBV during the last 28 years, including the first 8 cases treated with hematopoietic stem cell transplantation in the United States. Most cases of CAEBV have been reported from Japan. Unlike CAEBV in Japan, where EBV is nearly always found in T or natural killer (NK) cells in tissues, EBV was usually detected in B cells in tissues from our patients. Most patients presented with lymphadenopathy and splenomegaly; fever, hepatitis, and pancytopenia were common. Most patients died of infection or progressive lymphoproliferation. Unlike cases reported from Japan, our patients often showed a progressive loss of B cells and hypogammaglobulinemia. Although patients with CAEBV from Japan have normal or increased numbers of NK cells, many of our patients had reduced NK-cell numbers. Although immunosuppressive agents, rituximab, autologous cytotoxic T cells, or cytotoxic chemotherapy often resulted in short-term remissions, they were not curative. Hematopoietic stem cell transplantation was often curative for CAEBV, even in patients with active lymphoproliferative disease that was unresponsive to chemotherapy. These studies are registered at http://www.clinicaltrials.gov as NCT00032513 for CAEBV, NCT00062868 and NCT00058812 for EBV-specific T-cell studies, and NCT00578539 for the hematopoietic stem cell transplantation protocol.

Hepatocellular apoptosis associated with cytotoxic T/natural killer-cell infiltration in chronic active EBV infection

The aim of the present study was to identify the mechanism of hepatocellular apoptosis induced by EBV-infected cytotoxic T/natural killer (NK) cells in chronic active EBV infection (CAEBV). Eight patients with CAEBV were studied, and infected T-cell expansion and NK-cell expansion were detected in four patients each. Biopsy or necropsy was performed on lymph node, liver, or spleen, and each specimen was subjected to immunohistochemical double staining of CD3 plus caspase-3 with the addition of cytotoxic markers of T-cell restricted intracellular antigen-1 (TIA-1), perforin, and granzyme B, as well as EBV in situ hybridization (EBV-ISH). In the liver, some of the infiltrating CD3-positive lymphocytes stained positively for EBV-ISH and cytotoxic markers. Double staining of CD3 plus caspase-3 indicated caspase-3 positive hepatocytes with apoptotic features, accompanied by extensive infiltration of CD3-positive cells, which were directly attached to the apoptotic caspase-3 positive hepatocytes. In contrast, far fewer cells stained positive for caspase-3 in lymph node and spleen than in liver. The present findings suggest that in patients with CAEBV, cytotoxic T/NK cells may directly induce hepatocytes to undergo apoptosis more frequently than they do cells in other organs of the reticulo-endothelial system.

Clonality analysis by sequence variation of the latent membrane protein 1 gene in patients with chronic active Epstein-Barr virus infection

Chronic active Epstein-Barr virus (EBV) infection is a severe systemic disease associated with high rates of mortality and morbidity. Recent studies suggest that the clonal expansion of EBV-infected T or natural killer cells plays a crucial role in the pathogenesis of chronic active EBV infection. However, it is not clear whether chronic active EBV infection is truly a monoclonal disorder that originates from one cell. The clonality of EBV was investigated by sequence variation of the latent membrane protein 1 (LMP1) gene, which has a high degree of sequence heterogeneity. Peripheral blood mononuclear cells were obtained from nine Japanese patients with chronic active EBV infection and four with infectious mononucleosis. A carboxyl-terminal region of the LMP1 gene was analyzed by polymerase chain reaction (PCR). The amplified PCR products were subcloned, and 18 clones from each sample were sequenced. Patients with chronic active EBV infection each had two to five different LMP1 nucleotide sequences, whereas patients with infectious mononucleosis each had one to seven different sequences. Patients with chronic active EBV infection and infectious mononucleosis both had one dominant sequence. Longitudinal analysis was performed in four patients with chronic active EBV infection, in whom the dominant strains were found to have remained unchanged for several years. The results suggest that EBV in patients with chronic active EBV infection was polyclonal, although clonal expansion may occur. Collectively, these findings are critical to clarify further the pathogenesis of chronic active EBV infection and aid in the development of effective treatment strategies.

Chronic active Epstein-Barr virus infection associated with mutations in perforin that impair its maturation

Chronic active Epstein-Barr virus infection (CAEBV) is a rare disease in which previously healthy persons develop severe, life-threatening illness. Mutations in the perforin gene have been found in familial hemophagocytic lymphohistiocytosis, which shares some features with CAEBV. We studied a patient who died at age 18, 10 years after the onset of CAEBV. The patient had high titers of antibodies to EBV, EBV RNA in lymph nodes, T-cell lymphoproliferative disease, and hemophagocytic lymphohistiocytosis. DNA sequencing showed novel mutations in both alleles of the perforin gene that resulted in amino acid changes in the protein. The quantity of the native form of perforin from the patient's stimulated peripheral blood mononuclear cells (PBMCs) was extremely low and immunoblotting showed accumulation of an uncleaved precursor form of perforin. Stimulated PBMCs from the patient were defective for Fas-independent cytotoxicity. These data imply that mutations in this patient resulted in reduced perforin-mediated cytotoxicity by his lymphocytes. This is the first case in which perforin mutations have been shown to result in accumulation of the uncleaved, immature form of perforin. Mutations in the perforin gene are associated with some cases of CAEBV with hemophagocytic lymphohistiocytosis.

Biclonal expansion of T cells infected with monoclonal Epstein-Barr virus (EBV) in a patient with chronic, active EBV infection

Recent studies have suggested that a high percentage of Epstein-Barr virus (EBV)-infected lymphocytes in peripheral blood of patients with chronic, active EBV infection (CAEBV) is of T cell origin. Although T cells are expanded oligoclonally in CAEBV, it is not clear whether the restricted diversity of T cells arise from immune reaction against EBV-related antigens or from proliferation of EBV-infected cells. We experienced a patient with CAEBV who had biclonal expansion of peripheral blood T cells. We identified clonotypes of these two T cell clones in detail and purified the T cell clones. EBV infected mainly the two T cell clones, whereas the viral loads in peripheral blood cells other than these T cell clones were low or undetectable. The EBV strains infecting the two T cells clones were indistinguishable from each other by a series of genotype analyses of the virus. These results suggest that the two T cell clones infected with the same monoclonal EBV proliferated in peripheral blood of the patient.

Overview of Epstein-Barr virus-associated diseases in Japan

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

Presence of natural killer-cell clones with variable proliferative capacity in chronic active Epstein-Barr virus infection

Chronic active Epstein-Barr virus infection (CAEBV) is a syndrome that takes diverse clinical courses and is often associated with lymphoproliferative disorders of T/natural killer (NK)-cell lineage. We describe a patient with CAEBV associated with persistent pharyngeal ulcer, and with subsequent nasal T/NK-cell lymphoma in her neck lymph nodes and nasopharynx. Immunophenotyping of lymphoid cells showed that the lineage of Epstein-Barr virus (EBV)-positive cells in the patient was of NK-cell origin. By means of high-dose recombinant interleukin-2, we established an EBV-positive cell line of NK-cell lineage from her peripheral blood. Southern blot analysis for the number of terminal repeat sequences of EBV detected three NK-cell clones in the patient's lymph node. One of these clones was identical to the established cell line but was not observed in the pharyngeal ulcer, while the other two clones were present in the pharyngeal ulcer. These results suggest that the patient had expansion of the three NK-cell clones, one of which had proliferative capacity in vitro and was involved in the formation of the lymphoma. Moreover, the results suggest that the proliferative capacity of EBV-positive cells can be variable even in a single patient, and this variability may explain the clinical diversity in CAEBV.

Chronic, active Epstein-Barr virus infection

Chronic active Epstein-Barr virus (EBV) infection is an uncommon outcome of EBV infection and may present as a waxing and waning or fulminant syndrome. Unlike acute infectious mononucleosis, wherein EBV establishes lifelong infection and survives by maintaining a delicate balance with the host as a latent infection, in chronic active EBV infection the host-virus balance is disturbed. The mechanisms by which this balance becomes perturbed are likely to be heterogenous and may involve host immune factors, viral factors, or both. A number of subtle immunologic defects have been reported in patients with chronic active EBV infection. Enhanced expression of viral genes has also been noted in some cases. Treatment of chronic active EBV infection has proven difficult, but new modalities including etoposide-based regimens and adoptive transfer of EBV-specific cytotoxic T lymphocytes have shown promise.

Restricted diversification of T-cells in chronic active Epstein-Barr virus infection: potential inclination to T-lymphoproliferative disease

To assess the abnormal T-cell expansion in chronic active Epstein-Barr virus infection (CAEBV), T-cell antigen receptor (TCR) repertoire was analyzed in four patients with the disease. All fulfilled the diagnostic criteria of CAEBV, presenting with fever, hepatosplenomegaly, cytopenia, abnormal high titers of anti EBV-antibodies, and positive EBV genome of unknown cause. Southern blotting probed with EBV-terminal repeats and TCR Cbeta gene indicated clonal expansion of the infected cells in 3 and 2 patients, respectively. The number of CD4+ HLA-DR+ cells appreciably increased in patients 1 (59%) and 2 (24%), who had a coronary aneurysm and central nervous system involvement, respectively. TCR gene expression examined by the inverse polymerase chain reaction methods revealed that Vbeta gene usages were preferential in all patients (Vbeta7 and Vbeta12: patient 1, Vbeta4: patient 2, Vbeta13: patients 3 and 4), compared with those in healthy controls. Valpha18 gene expression was remarkably high in patients 1 and 2. Moreover, Jbeta gene expression was skewing in the reigning Vbeta clones in all patients. Vbeta4-Jbeta1.5 and Vbeta13-Jbeta1.5 genes were clonally expressed in patients 2 and 4, respectively. These results suggest that CAEBV is associated with the restricted diversity of T-cells, which may stem from the sustained expansion of oligoclonal T-cells possibly driven by conventional viral antigens, but not, superantigens. Although the study is limited by the small number of patients, the unbalanced T-cell repertoire might contribute to the evolution of T-lymphoproliferative disease, otherwise, imply the innate defective immunity to EBV in CAEBV patients.

CD95 (Fas) ligand expression of Epstein-Barr virus (EBV)-infected lymphocytes: a possible mechanism of immune evasion in chronic active EBV infection

The Epstein-Barr virus (EBV) induces infectious mononucleosis (IM) and can be associated with chronic active EBV infection (CAEBV). Cytotoxic T lymphocytes (CTL) play an important role in excluding EBV-infected cells. Two cytotoxic mechanisms of CTL have been demonstrated: one perforin/granzyme-based and the other Fas (CD95)/Fas ligand (FasL)-based. To clarify these two pathways in CAEBV, we analyzed six patients with CAEBV and four patients with IM using immunohistochemical staining of the lymph nodes. In both CAEBV and IM, CD8+ T-cells increased in number, but CD56+ natural killer cells were rare. In four of six cases with CAEBV, approximately half the lymphocytes were positive for T cell-restricted intracellular antigens (TIA-1), which were recognized by the cytolytic granules of CTL. In IM, the number of TIA-1 positive cells was smaller than that in CAEBV. Fas-positive lymphocytes were frequently encountered in both CAEBV and IM. However, FasL-positive lymphocytes increased in three of six patients with CAEBV, but not in patients with IM. Except for one case with CAEBV, the number of perforin- and/or granzyme-positive cells was small in number in both CAEBV and IM cases. In double-staining FasL and EBV in situ hybridization, FasL-positive EBV-infected lymphocytes were detected in CAEBV but not in IM. In CAEBV, the Fas/FasL pathway and not perforin pathways appears to play an important role in the pathogenesis. The data suggest that EBV-infected lymphocytes may evade immune attack through the expression of FasL.

Clinicopathological study of severe chronic active Epstein-Barr virus infection that developed in association with lymphoproliferative disorder and/or hemophagocytic syndrome

Chronic active Epstein-Barr virus (CAEBV) infection has been previously reported to be sometimes associated with an aggressive clinical course. However, the role of EBV in the CAEBV is not well clarified. A retrospective study was performed on nine adult and five child patients (eight males and six females). Histologically, at first admission, the presence of neoplastic lesions could not be confirmed. The lymph nodes in half of all cases revealed paracortical hyperplasia with transformed lymphocytes (hyperplastic type). Half of the cases showed non-suppurative necrosis and an increased number of histiocytes with phagocytosis (histiocytic type). Activated histiocytes with lymphokine positivity were frequently detected in the histiocytic type. In the phenotypical study, 10 of the examined 11 cases showed increased numbers of natural killer (NK) cells and/or CD8-positive T lymphocytes. In situ hybridization (ISH) showed EBV-infected lymphoid cells, but the number of EBV-infected cells varied. Double-labeling immunochemistry/ISH demonstrated EBV-infected T cells, including NK cells, but not B cells. In addition, three cases showed a monoclonal dissemination of EBV terminal repetitive sequence (TR), and two cases showed oligoclonal dissemination. From those findings, monoclonal, oligoclonal and polyclonal populations of EBV-infected T or NK cells were considered to be present in CAEBV states. During the clinical course, 12 of the 14 cases died within 5 years. Six cases died from EBV-associated hematopoietic tumors (histiocytic tumor, T cell lymphoma, B cell lymphoma, plasmacytoma, and NK cell leukemia); one from non-EBV-associated acute myelogenous leukemia, and five due to hemophagocytic syndrome. The examined EBV-associated hematopoietic tumors showed monoclonal EBV terminal repetitive sequences. There is a possibility that the monoclonal dissemination of EBV-infected cells develops from oligoclonal or polyclonal EBV-infected cells. And active histiocytes with lymphokine positivity were frequently detected in the cases with histologically histiocytic type. These findings seem to be related with the causes of death due to hemophagocytic syndrome.

Epstein-Barr viral gene expression in B-lymphocytes

The strategy of the Epstein-Barr virus to persist lifelong in the host depends on establishing a reservoir, which cannot be detected by the immune system but allows reactivation of the virus for shedding and transmission to a new host. Epithelial cells and B-cells play a major role in this viral strategy of EBV, since differentiating epithelial tissues were shown to be permissive for lytic replication in vivo, whereas the B-lymphocytes become predominantly latently infected. However, which cells are the reservoir and which the sites of lytic replication are not quite clear. With the technique of reverse transcription, PCR and immunohistochemistry, we demonstrated that the B-cells of the peripheral blood are a major site of virus production during the primary infection during infectious mononucleosis. These permissive B-cells were also detected after convalescence, however, the absence of any lytic transcripts suggested an efficient immunological control very early in the viral lytic cycle. Serological data on reactivation of EBV correlated with the detection of lytic cycle transcripts in the blood and thus demonstrated that the site of virus production during infectious mononucleosis must be different from that of the persistent state. In those cases, where the infection takes a chronic active course, control of lytic replication is insufficient, either on the level of immune surveillance or of viral gene regulation. We have demonstrated a virus strain with a lytic phenotype in an individual suffering chronic active infection. The impaired capability of this virus to immortalise B-cells correlated with an enhanced expression of the lytic switch gene BZLF-1 and down-regulation of latent regulatory genes in the early phase of infection.