Epstein-Barr virus sustains Burkitt's lymphomas and Hodgkin's disease

Two proteins of Epstein-Barr Virus make formerly unrecognized contributions to maintaining the tumors of Burkitt's lymphomas and Hodgkin's disease. The Epstein-Barr nuclear antigen 1 (EBNA1) protein can support the synthesis and maintenance of the viral genome. New data show that inhibiting EBNA1 in Burkitt's lymphoma cells induces cell death by apoptosis. Therefore, EBNA1 inhibits apoptosis and, according to recent findings, does so independently of other viral genes. The latent membrane protein 2a (LMP2a) binds to signaling molecules that are engaged by the B-cell receptor and inhibits the signaling that is mediated by antigen binding. New findings have revealed how LMP2a overcomes the apoptosis that normally results from the absence of functional B-cell receptors, and explain how Hodgkin's disease tumor cells, which are B cells, survive but lack functional antibodies.     

Immunity to Epstein-Barr virus in Hodgkin's disease preceded by infectious mononucleosis

A patient who developed Hodgkin''s disease four years after infectious mononucleosis had elevated serum antibody titres to Epstein-Barr virus and delayed hypersensitivity reactions to membrane antigens prepared from fresh autologous spleen, from spleen cells of another Hodgkin''s patient, and from cell lines known to carry the Epstein-Barr virus genome. Additional studies in more lymphoma patients will be needed to determine the significance of the reactivity against tumour and virus-associated antigens which has been documented in this patient.     

Chronic fatigue syndrome. A critical appraisal of the role of Epstein-Barr virus.

The symptom complex currently designated the chronic fatigue syndrome was previously termed the chronic or chronic active Epstein-Barr virus syndrome or the chronic mononucleosis syndrome, prematurely assuming an etiologic role for the Epstein-Barr virus (EBV). This presumption derived from the fact that some patients with the chronic fatigue syndrome have very high or very low titers of certain antibodies to EBV. A review of seroepidemiologic patterns of response to EBV and of studies of patients with the chronic fatigue syndrome shows that these antibody titers overlap considerably both with those of controls or other healthy persons and with those of patients with other illnesses. Given the high prevalence of exposure to EBV, it would be difficult to determine whether the virus caused the syndrome or whether the antibody elevations resulted from the illness, even if distinct differences in titers existed. Other methodologic issues of control selection, laboratory test comparability, and differing case definitions pose problems in studying this syndrome. The recently published working case definition should facilitate the continuing search for causes.     

Clonal origins of lymphoproliferative disease induced by Epstein-Barr virus.

Analysis of immunoglobulin gene rearrangements in 16 B-cell lineages clonally propagated from two mononucleosis patients supported the notion that mononucleosis is a polyclonal B-lymphoproliferative disorder. Three of seven cell clones from a patient with a fatal B lymphoma revealed the same pattern of immunoglobulin gene rearrangement, indicating that this patient's disease was oligoclonal. The three similar clones were propagated from two sites (blood and spleen), indicating that they represent a metastatic cell lineage which arose during the patient's fatal B lymphoproliferation.     

Reed-Sternberg cells and "bystander" lymphocytes in lymph nodes affected by Hodgkin's disease are infected with different strains of Epstein-Barr virus.

In most cases of Epstein-Barr virus (EBV)-associated Hodgkin's disease (HD), EBV-positive Reed-Sternberg (RS) cells and rare EBV-positive reservoir lymphocytes coexist in lymph nodes. Here we show that, in two cases of EBV-associated HD, strains infecting RS cells and reservoir lymphocytes of the same patient have different BNLF-1 genes. This suggests that RS cells and reservoir lymphocytes of the same patient are infected by different EBV strains.     

DNA of Epstein-Barr virus. V. Direct repeats of the ends of Epstein-Barr virus DNA.

Previous data indicated that Epstein-Barr virus DNA is terminated at both ends by direct or inverted repeats of from 1 to 12 copies of a 3 X 10(5)-dalton sequence. Thus, restriction endonuclease fragments which include either terminus vary in size by 3 X 10(5)-dalton increments (D. Given and E. Kieff, J. Virol. 28:524--542, 1978; S. D. Hayward and E. Kieff, J. Virol. 23:421--429, 1977). Furthermore, defined fragments containing either terminus hybridize to each other (Given and Kieff, J. Virol. 28:524--542, 1978). The 5' ends of the DNA are susceptible to lambda exonuclease digestion (Hayward and Kieff, J. Virol. 23:421--429, 1977). To determine whether the terminal DNA is a direct or inverted repeat, the structures formed after denaturation and reannealing of the DNA from one terminus and after annealing of lambda exonuclease-treated DNA were examined in the electron microscope. The data were as follows. (i) No inverted repeats were detected within the SalI D or EcoRI D terminal fragments of Epstein-Barr virus DNA. The absence of "hairpin- or pan-handle-like" structures in denatured and partially reannealed preparations of the SalI D or EcoRI D fragment and the absence of repetitive hairpin- or pan-handle-like structures in the free 5' tails of DNA treated with lambda exonuclease indicate that there is no inverted repeat within the 3 X 10(5)-dalton terminal reiteration. (ii) Denatured SalI D or EcoRI D fragments reanneal to form circles ranging in size from 3 X 10(5) to 2.5 X 1O(6) daltons, indicating the presence of multiple direct repeats within this terminus. (iii) Lambda exonuclease treatment of the DNA extracted from virus that had accumulated in the extracellular fluid resulted in asynchronous digestion of ends and extensive internal digestion, probably a consequence of nicks and gaps in the DNA. Most full-length molecules, after 5 min of lambda exonuclease digestion, annealed to form circles, indicating that there exists a direct repeat at both ends of the DNA. (iv) The finding of several circularized molecules with small, largely double-strand circles at the juncture of the ends indicates that the direct repeat at both ends is directly repeated within each end. Hybridization between the direct repeats at the termini is likely to be the mechanism by which Epstein-Barr virus DNA circularizes within infected cells (T. Lindahl, A. Adams, G. Bjursell, G. W. Bornkamm, C. Kaschka-Dierich, and U. Jehn, J. Mol. Biol. 102:511-530, 1976).     

Proteins of Epstein-Barr virus. I. Analysis of the polypeptides of purified enveloped Epstein-Barr virus.

Epstein-Barr virus (EBV) was purified from the extracellular fluid of HR-1 and B95-8 cell lines. The preparations of purified virus consisted of enveloped particles and had EBV-specific antigneic reactivity. Comparison of the amount of labeled protein in preparations of virus purified from cultures incubated in [35S]methionine with the amount of labeled protein in preparations obtained following a mixture of unlabeled virus with [35S]methionine-labeled cellular proteins indicated that less than 2% of the labeled protein in the purified virus preparation could be attributed to contamination with labeled cellular proteins. No extraneous membranous material was seen in thin sections of the purified virus preparations. Analysis of the polypeptides of purified enveloped EBV indicated the following. (i) Eighteen polypeptides could be resolved in Coomassie brilliant blue-stained electropherograms of extracellular virus purified from HR-1 and B95-8 cultures. (ii) Thirty-three polypeptides could be resolved in fluorograms of labeled EBV purified from B95-8 cultures and subjected to electrophoresis in acrylamide gels cross-linked with diallyltartardiamide. The molecular weight of the EBV polypeptides was estimated by co-electrophoresis with the polypeptides of purified herpes simplex virus and purified polypeptides of known molecular weight to range from 28 x 10(3) to approximately 290 x 10(3) (iii) The polypeptides of EBV could be grouped by their relative molar abundancy into three classes: VP6, 7, and 27 present in high abundance; VP1, 12, 20, 23, and 29 present in moderate abundance; and a third class of less abundant polypeptides, VP4, 5, 8, 9, 10, 11, 15, 16, 21, and 22. The remainder of the polypeptides could not be precisely quantitated. (iv) The polypeptides of purified EBV, although similar in number and in range of molecular weight to the polypeptides of purified herpes simplex virus, differ sufficiently from those of herpes simplex virus so as to preclude comparison of individual polypeptide components.     

Analysis of Epstein-Barr virus strains and variants in classical Hodgkin's lymphoma by laser microdissection

Epstein-Barr virus (EBV) seems to have an etiological role in the pathogenesis of classical Hodgkin's lymphoma (cHL). Studies of whole tissue DNA by polymerase-chain reaction (PCR) have shown a considerable number of cHL cases with co-infections by different EBV strains and variants, which apparently contradict the clonality of EBV in cHL previously demonstrated by Southern blot analysis. Due to the paucity of HRS cells in HL tissues, studies on single cell DNA are necessary to identify the specific cellular location (HRS cells and/or bystander B lymphocytes) of the EBV strains and variants present in tissue specimens. In the current study, the presence of EBV was determined by PCR of the 3' end of the LMP-1 gene and EBNA-3C gene in whole tissue and, consecutively, in isolated cells from 26 cases of cHL: 10 HIV-positive and 16 sporadic cHL cases. EBV EBERs were present in all but 2 sporadic cHL cases, which were used as negative controls. At isolated cell level, EBNA-3C gene PCR was more sensitive. Indeed, from the cHL cases in which dual-infection was present, it was observed that, in most of them, HRS cells were infected by type 1 virus, and B lymphocytes were co-infected by both types, which points towards EBV infection occurring early in cHL development. Moreover, the finding of 2 cases with dual-infection in HRS may suggest that, in a small percentage of cHL cases, HRS cells derive from different neoplastic clones, or that HRS cells are superinfected by other viral types after the establishment of the neoplastic clone.     

Biology and disease associations of Epstein-Barr virus

Epstein-Barr virus (EBV) is a human herpesvirus which infects almost all of the world's population subclinically during childhood and thereafter remains in the body for life. The virus colonizes antibody-producing (B) cells, which, as relatively long-lived resting cells, are an ideal site for long-term residence. Here EBV evades recognition and destruction by cytotoxic T cells. EBV is passed to naive hosts in saliva, but how the virus gains access to this route of transmission is not entirely clear. EBV carries a set of latent genes that, when expressed in resting B cells, induce cell proliferation and thereby increase the chances of successful virus colonization of the B-cell system during primary infection and the establishment of persistence. However, if this cell proliferation is not controlled, or if it is accompanied by additional genetic events within the infected cell, it can lead to malignancy. Thus EBV acts as a step in the evolution of an ever-increasing list of malignancies which are broadly of lymphoid or epithelial cell origin. In some of these, such as B-lymphoproliferative disease in the immunocompromised host, the role of the virus is central and well defined; in others, such as Burkitt's lymphoma, essential cofactors have been identified which act in concert with EBV in the evolution of the malignant clone. However, in several diseases in which the presence of EBV has more recently been discovered, the role of the virus is unclear. This review describes recent views on the EBV life cycle and its interlinks with normal B-cell biology, and discusses how this interrelationship may be upset and result in EBV-associated disease.