Detection of the latent form of Epstein-Barr virus DNA in the peripheral blood of healthy individuals.

Epstein-Barr virus infects resting B cells in vitro and activates them to continuously proliferating lymphoblasts. Activation is essential for the virus to convert its linear genome to the covalently closed circular episomal form in which it persists in proliferating cells. However, in vivo, Epstein-Barr virus persists in resting B cells. We found that in these cells also the virus is present as an episome, suggesting that the cells must, at some time, have been activated and then returned to a resting state. This is the first direct demonstration, for any herpesvirus, of this form of the viral genome in normal persistently infected tissue. Since no linear viral DNA was detected, we estimate that fewer than 1 in 40 cells replicates the virus in the peripheral blood of healthy donors.     

Immunoglobulin properties of Epstein-Barr virus transformed human umbilical cord and adult peripheral blood lymphocytes

We have observed that a subset of E+ cells bind human monomeric IgG (FcR-IgG). In the present study, we have separated the E+, FcR-IgG+ cells by flow cytometry and tested their NK activity against the tumor KS62 using the chromium-release assay. Virtually all the NK activity residing within the E+ subset was mediated by E+, FcR-IgG+ cells. These findings are discussed in relation to the cellular lineage of the human NK cell.     

Pathophysiologic analysis of peripheral blood lymphocytes from patients with primary immunodeficiency. I. Ig synthesis by peripheral blood lymphocytes stimulated with either pokeweed mitogen or Epstein-Barr virus in vitro

In the present study 5 patients with common variable hypogammaglobulinemia (CVH) and 4 patients with selective IgA deficiency (IgA-D) were analyzed for the cellular defects responsible for impaired Ig synthesis with use of peripheral blood lymphocytes stimulated with either PWM or EBV in vitro. By the use of co-culture with PWM, all the patients examined had intrinsic B cell defects restricted to the synthesis of Ig class corresponding to the low or absent Ig class(es) in the sera. Two types of excessive suppressor T activity were found, which were abrogated by irradiation. One was isotype-nonspecific and the other was IgA-specific. Moreover, failure of IgA-specific helper T activity was demonstrated. The use of EBV as an agent that polyclonally activates B cells independently of T cells and monocytes should allow a clearer delineation of the level of the B cell defects. When co-cultured with EBV, B cells from 3 patients with CVH produced normal to subnormal quantities of IgM although they could produce no IgM upon co-culturing with normal T cells and PWM. B cells from 2 patients with CVH could produce IgM normally by stimulation with either PWM or EBV; however, there was no restoration to produce IgG or IgA in these patients. In addition, B cells from 2 patients with IgA-D produced not only IgG and IgM but also IgA almost normally at 4 days after in vitro stimulation with EBV.     

Differences in B cell growth phenotype reflect novel patterns of Epstein-Barr virus latent gene expression in Burkitt''s lymphoma cells.

Recently established Epstein-Barr virus (EBV)-positive Burkitt's lymphoma (BL) cell lines, carrying chromosomal translocations indicative of their malignant origin, have been monitored for their degree of in vitro progression towards a more 'lymphoblastoid' cell surface phenotype and growth pattern, and for their expression of three EBV latent gene products which are constitutively present in all virus-transformed normal lymphoblastoid cell lines (LCLs). BL cell lines which stably retained the original tumour biopsy phenotype on serial passage were all positive for the nuclear antigen EBNA 1 but did not express detectable amounts of two other 'transforming' proteins, EBNA 2 and the latent membrane protein (LMP). This novel pattern of EBV gene expression was also observed on direct analysis of BL biopsy tissue. All three viral proteins became detectable, however, in BL cell lines which had progressed towards a more LCL-like phenotype in vitro. This work establishes a link between B cell phenotype and the accompanying pattern of EBV latent gene expression, and identifies a novel type of EBV:cell interaction which may be unique to BL cells.     

Persistent Epstein-Barr virus infection in a human T-cell line: unique program of latent virus expression.

The growth transforming potential of Epstein-Barr virus (EBV) for Burkitt's lymphoma and nasopharyngeal carcinoma is now extended to other neoplasia, such as Hodgkin's disease, peripheral T-cell tumor and gastric cancer. We have generated an EBV recombinant with a selectable marker at the viral thymidine kinase locus. Recombinant EBV was successfully infected into a human T-cell line, MT-2. Following incubation in the selective medium, drug resistant MT-2 cell clones were isolated and proved to be infected with recombinant EBV. EBV-infected MT-2 cell clones expressed EBNA 1 and LMP 1 and very little of EBNA 2, showing the BamHI F promoter-driven latency II form of infection, which is seen in non-B-cell tumors. This is the first report of in vitro generation of latency II type EBV infection. The present system of persistent EBV infection in T cells should be a good model for investigating the pathogenic role of EBV in non-B-cell tumors.     

ABCA1 gene expression in peripheral blood lymphocytes and macrophages in patients with atherosclerosis

ABCA1 transporter is known to play important role in the cholesterol transport from peripheral tissues. However its contribution in atherosclerosis development remains not completely understood. Using Real Time PCR, a significant reduction of ABCA1 mRNA level in leukocytes of patients with atherosclerosis was determined when compared with controls. Mean ABCA1 expression levels in leukocytes for the group of patients and for the control group are 0.57 +/- 0.28 and 0.93 +/- 0.14 (p = 0.02). At the same time we detected a significant increase of ABCA1 mRNA level in macrophages of patients when compared with controls. Mean ABCA1 expression levels in macrophages for the group of patients and for the control group are 1.32 +/- 0.10 and 0.90 +/- 0.14 (p = 0.014). In summary, we suggest that expression level of ABCA1 gene may contribute to the development of atherosclerosis.     

Epstein-Barr virus nuclear antigen 2 induces expression of the virus-encoded latent membrane protein.

Infection of Epstein-Barr virus-negative human B-lymphoma cell lines with the fully transforming B95.8 Epstein-Barr virus strain was associated with complete virus latent gene expression and a change in the cell surface and growth phenotype toward that of in vitro-transformed lymphoblastoid cell lines. In contrast, the cells infected with the P3HR1 Epstein-Barr virus strain, a deletion mutant that cannot encode Epstein-Barr nuclear antigen 2 (EBNA2) or a full-length EBNA-LP, expressed EBNAs1, 3a, 3b, and 3c but were negative for the latent membrane protein (LMP) and showed no change in cellular phenotype. This suggests that EBNA2 and/or EBNA-LP may be required for subsequent expression of LMP in Epstein-Barr virus-infected B cells. Recombinant vectors capable of expressing the B95.8 EBNA2A protein were introduced by electroporation into two P3HR1-converted B-lymphoma cell lines, BL30/P3 and BL41/P3. In both cases, stable expression of EBNA2A was accompanied by activation of LMP expression from the resident P3HR1 genome; control transfectants that did not express the EBNA2A protein never showed induction of LMP. In further experiments, a recombinant vector capable of expressing the full-length B95.8 EBNA-LP was introduced into the same target lines. Strong EBNA-LP expression was consistently observed in the transfected clones but was never accompanied by induction of LMP. The EBNA2A gene transfectants expressing EBNA2A and LMP showed a dramatic change in cell surface and growth phenotype toward a pattern like that of lymphoblastoid cell lines; some but not all of these changes could be reproduced in the absence of EBNA2A by transfection of P3HR1-converted cell lines with a recombinant vector expressing LMP. These studies suggest that EBNA2 plays an important dual role in the process of B-cell activation to the lymphoblastoid phenotype; the protein can have a direct effect upon cellular gene expression and is also involved in activating the expression of a second virus-encoded effector protein, LMP.     

Replication of latent Epstein-Barr virus genomes in Raji cells.

The replication of the 50 to 60 latent, predominantly extrachromosomal, Epstein-Barr virus genomes maintained by the Burkitt-lymphoma-derived Raji cell line was investigated by using a Meselson-Stahl density transfer approach. Samples of DNA isolated from cells cultivated for different periods in bromodeoxyuridine-supplemented medium were fractionated according to density, and the distribution of viral and cellular DNAs among the heavy-, hybrid-, and light-density species was quantitated. The results indicate that the majority of latent Epstein-Barr virus DNA plasmids each replicate once during the cell cycle.     

Age-related differences in integrin expression in peripheral blood lymphocytes

Alpha integrins play an important role in cell to cell and cell to extra-cellular matrix interactions required for an effective T-lymphocyte-mediated immune response, however little is known about age related differences in expression of alpha integrins on T-cells in humans. We here measured alpha-4 (α4) integrin (CD49d) expression on T-lymphocytes via peripheral blood sampling, comparing parameters between cohorts of young and old adults. No age-related differences were found for the absolute numbers of T-cells, although the percentage of CD4+ T-cells in older adults was significantly greater and the percentage of CD8+ T-cells lower than in younger cohorts. Percentage and absolute numbers of CD3+ T-cells co-expressing CD49d were significantly lower in older adults compared to younger cohorts, and the percentage of gated CD4+ and CD8+ cells that co-labelled positively for CD49d was also reduced in this group. There were no age-related differences in circulating levels of cytokines (Type I interferons) that are known to regulate cell surface integrin expression. Reduced expression of alpha integrins on T-cells may be an early indicator of the loss of homeostatic control that occurs with ageing, contributing to diminished effector T-cell responses during senescence.     

Identification of the Epstein-Barr virus terminal protein gene products in latently infected lymphocytes.

The terminal protein (TP) gene produces two overlapping mRNAs in latently infected lymphocytes that are predicted to encode the similar polypeptides TP1 (497 amino acids) and TP2 (378 amino acids), with TP1 exon 1 providing 119 extra unique residues at the N terminus. Rabbit antisera were raised to procaryotic fusion proteins and used to detect expression of a predicted 53-kilodalton (kDa) TP product in transfected 293 cells and latently infected lymphocytes. Fractionation of transfected 293 cells showed this protein to be localized to an integral membrane preparation. The same fraction of latently infected lymphocytes contained proteins of 53 and 27 to 39 kDa as determined by Western immunoblotting with the TP-specific rabbit antisera. Immunoprecipitation of TP products from 35S-labeled human lymphoblastoid cells (CR/B95-8) was used in pulse-chase experiments and showed that TP1 was a labile protein with a half-life of approximately 2 to 4 h. The anti-fusion protein serum detected a 53-kDa TP1 and degradation products in the range of 25 to 35 kDa. A panel of Burkitt's lymphoma cell lines and cell lines established with virus recovered from the BL cells were analyzed by Western immunoblotting and found to contain the 53-kDa TP1 product, its degradation products, or both. Only two EBV-positive BL cell lines (BL72 and Wewak II) were negative in this assay. The results suggest that a labile TP1 protein may be expressed by most, if not all, EBV-infected cell lines.     

A novel interleukin-12 p40-related protein induced by latent Epstein-Barr virus infection in B lymphocytes.

We have isolated a cDNA encoding a novel hematopoietin receptor family member related to the p40 subunit of interleukin-12 and to the ciliary neurotrophic factor receptor, whose expression is induced in B lymphocytes by Epstein-Barr virus (EBV) infection. This gene, which we have designated EBV-induced gene 3 (EBI3), encodes a 34-kDa glycoprotein which lacks a membrane-anchoring motif and is secreted. Despite the absence of a membrane-anchoring motif and of cysteines likely to mediate covalent linkage to an integral membrane protein, EBI3 is also present on the plasma membrane of EBV-transformed B lymphocytes and of transfected cells. Most newly synthesized EBI3 is retained in the endoplasmic reticulum in an endoglycosidase H-sensitive form associated with the molecular chaperone calnexin and with a novel 60-kDa protein. EBI3 is expressed in vivo by scattered cells in interfollicular zones of tonsil tissue, by cells associated with sinusoids in perifollicular areas of spleen tissue, and at very high levels by placental syncytiotrophoblasts. EBI3 expression in vitro is induced in EBV-negative cell lines by expression of the EBV latent infection membrane protein-1 and in peripheral blood mononuclear cells by pokeweed mitogen stimulation. EBI3 maps to chromosome 19p13.2/3, near genes encoding the erythropoietin receptor and the cytokine receptor-associated kinase, Tyk2. EBI3 synthesis by trophoblasts and by EBV-transformed cells and similarities to interleukin-12 p40 are compatible with a role for EBI3 in regulating cell-mediated immune responses.     

Autonomic and glucocorticoid associations with the steady-state expression of latent Epstein-Barr virus

Previous studies have demonstrated the impact of psychological stress on the steady-state expression/reactivation of latent Epstein-Barr virus (EBV). Stress-induced decrements in the cellular immune response result in less control over the expression of the latent virus, resulting in increases in antibody to the virus. In Study 1, we investigated whether the steady-state expression of latent EBV in vivo differed between high and low stress reactors, as defined by sympathetic cardiac reactivity. Autonomic activity and antibody titers to Epstein-Barr virus capsid antigen (VCA) were measured in 50 elderly women latently infected with EBV. Results revealed that women who were high stress reactors were characterized by higher antibody titers to the latent virus than low stress reactors. High reactors tended to show larger stress-related increases in cortisol than low reactors, but the differences were not significant. Daily stressors can activate the autonomic nervous system and promote the release of pituitary and adrenal hormones, especially in high reactors. Glucocorticoid hormones have been shown to reactivate EBV in vitro from cells latently infected with the virus. We hypothesized that absolute levels of plasma cortisol may not be the only explanation for stress-induced reactivation of latent EBV and that the diurnal changes in the production of cortisol may be an important factor in these interactions. To examine the feasibility of this hypothesis, an in vitro study was conducted (Study 2) to determine whether changing glucocorticoid concentrations in the medium, in which EBV latently infected cells were cultured, to mimic diurnal changes in plasma cortisol concentrations would enhance the reactivation of the latent virus. Cells latently infected with EBV were exposed to either constant or varying concentrations of the synthetic glucocorticoid hormone dexamethasone (Dex), for 72 h. Results revealed a three- to eightfold enhancement of reactivation of latent EBV in cells pulsed with varying Dex concentrations when compared with cells exposed to a constant and/or a higher mean level of one Dex concentration. Together, these studies raise the possibility that differences in the kinetics of glucocorticoid concentrations may contribute to differences in the reactivation of latent EBV.     

Epstein-Barr virus DNA is amplified in transformed lymphocytes.

Leukocytes isolated from two adult donors who lacked detectable antibodies to antigens associated with Epstein-Barr virus were exposed to an average of 0.02 to 0.1 DNA-containing particles of Epstein-Barr virus per cell and immediately clones in agarose. Within about 30 generations all transformed cell clones contained between 5 and 800 copies of viral DNA per cell. Only 1 in 10(4) to less than 1 in 10(5) of the cells of each clone release virus, and the frequency of release did not correlate with the average number of copies of viral DNA in the cells of each clone. One clone that had an average of five copies of viral DNA per cell was recloned, and the average number of copies in four of six subclones increased 15-to 50-fold while the subclones were being propagated sufficiently to study them. These results indicate that Epstein-Barr virus DNA can undergo amplification relative to cell DNA at different times after it transforms cells.