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A Calender

Publications and source records attributed to A Calender.

At least 73 records · Page 4Linked to original sources
PubMed1990

Modulation of cellular gene expression in B lymphoma cells following in vitro infection by Epstein-Barr virus (EBV).

In vitro infection of EBV-negative lymphoma cell lines with immortalizing strains of Epstein-Barr virus induces the cell-surface expression of B-cell markers, such as the EBV receptor/CR2 (CD21) and the CD23 antigen. The non-immortalizing EBV variant, P3HRI, which carries a deletion encompassing the EBV nuclear antigen 2 (EBNA2) gene, fails to induce any such expression. We show here that the EBV-mediated up-regulation of cell-surface expression of these molecules is associated with an increased level of the specific steady-state RNA corresponding to these 2 genes. These results suggest that the role of EBNA2 in B-cell growth and immortalization may be related to its role in transactivation of cellular genes. In order to identify other cellular genes whose expression may be modulated by EBV, we analyzed the level of transcription of a set of genes possibly involved in Burkitt's lymphoma pathogenesis. The level of the c-myc oncogene transcript was not significantly affected by in vitro EBV infection. The c-fgr oncogene, thought to be specifically activated in EBV-infected cells, was found to be expressed in some EBV-negative lymphoma cells and also to be activated by both non-immortalizing and immortalizing strains of EBV. The expression of vimentin, the major 56-kDa polypeptide of mesenchymal cell intermediate filaments, was altered by all EBV isolates, in either a negative or a positive way, depending on the cell line. Expression of lymphocyte-function-associated antigens, LFA-1 alpha/beta (CD11 a/18) and LFA-3 (CD58), involved in intercellular adhesion and the T-cytotoxic pathway, were differentially regulated by EBV; a crucial observation was the activation by immortalizing EBV isolates of LFA-1 beta chain (CD18) and of LFA-3 (CD58). The EBV-and possibly EBNA2-associated modulation of cellular genes, such as CR2 (CD21), CD23 and LFAs, probably represents key events for EBV-induced B-cell proliferation, and also for in vivo immune control of EBV-infected B cells.

Antigens, CD↗
PubMed1990

Low expression of lymphocyte function-associated antigen (LFA)-1 and LFA-3 adhesion molecules is a common trait in Burkitt's lymphoma associated with and not associated with Epstein-Barr virus.

Lymphocyte function-associated antigens 1 and 3 (LFA-1, LFA-3) and intercellular adhesion molecule 1 (ICAM-1) are cell surface adhesion molecules necessary for immune processes requiring intercellular contact. It was recently proposed that malignant Burkitt's lymphoma cells (BL) may escape from immunosurveillance through the downregulation of LFA-1 (CD11a/CD18) or LFA-3 (CD58) and ICAM-1 (CD54) molecules. Expression of these three adhesion antigens was investigated in 19 BL lines. LFA-1 or LFA-3 expression was found to be absent or low in 8 of 11 Epstein-Barr virus (EBV) genome positive BL, but strongly expressed on all nonmalignant EBV genome positive lymphoblastoid cell lines (LCL). Negative or weak expression of LFA-1 and LFA-3 was also observed in 7 of 8 EBV genome negative BL. ICAM-1 was found to be expressed on the cell surface of the majority of BL lines. BL lines growing as individual cells did not express LFA-1, whereas clump-forming BL lines expressed this marker involved in B-cell homotypic aggregation. Expression of LFA-1 and LFA-3 was induced on in vitro infection of EBV-negative BL cells with the immortalizing EBV strain B95-8, and weakly with the nonimmortalizing EBV strain P3HR1. EBNA2 and LMP, two EBV encoded proteins expressed in LCL and in BL infected with B95-8 (BL/B95-8), are not expressed in P3HR1 infected BL cells (BL/P3HR1). Stable expression of EBNA2 after gene transfer in a BL/P3HR1 cell line did not restore the level of LFA-1 and LFA-3 found on BL/B95-8 cells. In EBV-positive BL cells expressing LFA-1 and LFA-3, LMP was found coexpressed, supporting the recent finding of the role of LMP in B-cell adhesion receptor activation. Consequently, diminished LFA-1 and LFA-3 expression appears to be a common characteristic of numerous EBV-positive BL as well as EBV-negative BL. These findings are discussed in the framework of BL pathogenesis.

Antigens, CD↗
PubMed1990

Stable expression and function of EBV/C3d receptor following genomic transfection into murine fibroblast L cells.

The Epstein-Barr virus (EBV) and the C3d component of complement bind to the same cell surface receptor (EBVR/CR2) which is part of the B lymphocyte differentiation antigen recognized by the monoclonal antibodies (mAb) of the cluster of differentiation 21 (CD21). To analyze EBV and C3d binding to this receptor, mouse fibroblasts were transfected with human genomic DNA and rare CD21-positive cells were selected and cloned by cell sorting. The presence of the human gene in host cell DNA as well as its transcription product were assayed with a cloned EBVR/CR2 cDNA by Southern and Northern blotting analysis, respectively. A glycoprotein of apparent molecular mass of 140 kDa, similar to that found in human B lymphocytes, was immunoprecipitated with anti-CD21 mAb and proved to be functional since both C3d and EBV bound efficiently and specifically to mouse cells expressing EBVR/CR2. However, no expression of EBV nuclear antigens, early antigens and viral capsid antigens was detected in cells exposed to EBV. This indicates that the presence of EBVR/CR2 is not sufficient to allow full infection of mouse fibroblasts.

Animals↗
PubMed1990

Complement alternative pathway activation and control on membranes of human lymphoid B cell lines.

Membrane regulatory molecules normally prevent complement activation by autologous cells, therefore we compared the membrane control system of human lymphoid cell lines which activate or not human complement through the alternative pathway (AP). Membrane expression of decay-accelerating factor (DAF), membrane cofactor protein (MCP), complement receptors (CR)1, CR2 and H was measured either by radioimmunoassay or enzyme-linked immunosorbent assay on cell lysates. Soluble extracts of isolated membranes were tested functionally for their ability to accelerate the decay of C3bBb C3-convertase and allow the cleavage of C3b by factor I. Both regulatory functions were detected in solubilized membranes of Ramos cells, which do not activate the AP, as well as on the potent AP activator, Raji. Raji cells were found to express CR2, DAF and MCP molecules, while MCP was the only known regulatory protein detected on Ramos cells which expressed neither CR1, nor CR2, H or DAF. The I-cofactor activity of both Raji and Ramos cells was immunoprecipitated by anti-MCP, but the decay-accelerating activity was not adsorbed by anti-DAF nor by any of the available antibodies. Two EBV genome-negative cell lines (BJAB, BL41) were tested before and after in vitro conversion by EBV. As previously shown, EBV-converted cell lines activate the AP more efficiently than EBV- cell lines. At the same time, EBV superinfection induces an increase of both AP regulatory functions of cell membranes and enhances the expression of DAF, MCP and CR2. The results of this study show that complement activation by lymphoid cell lines is not related to an impaired autologous control of these cells, but that the expression of regulatory molecules increases together with the appearance of activating structures on the cell surface. Our results also suggest the occurrence of a new factor involved in the decay-accelerating activity on BL lines.

Antigens, CD↗
PubMed1990

Stable transfection of Epstein-Barr virus (EBV) nuclear antigen 2 in lymphoma cells containing the EBV P3HR1 genome induces expression of B-cell activation molecules CD21 and CD23.

A set of B-cell activation molecules, including the Epstein-Barr virus (EBV) receptor CR2 (CD21) and the B-cell activation antigen CD23 (Blast2/Fc epsilon RII), is turned on by infecting EBV-negative B-lymphoma cell lines with immortalizing strains of the viruslike B95-8 (BL/B95 cells). This up regulation may represent one of the mechanisms involved in EBV-mediated B-cell immortalization. The P3HR1 nonimmortalizing strain of the virus, which is deleted for the entire Epstein-Barr nuclear antigen 2 (EBNA2) protein open reading frame, is incapable of inducing the expression of CR2 and CD23, suggesting a crucial role for EBNA2 in the activation of these molecules. In addition, lymphoma cells containing the P3HR1 genome (BL/P3HR1 cells) do not express the viral latent membrane protein (LMP), which is regularly expressed in cells infected with immortalizing viral strains. Using electroporation, we have transfected the EBNA2 gene cloned in an episomal vector into BL/P3HR1 cells and have obtained cell clones that stably express the EBNA2 protein. In these clones, EBNA2 expression was associated with an increased amount of CR2 and CD23 steady-state RNAs. Of the three species of CD23 mRNAs described, the Fc epsilon RIIa species was preferentially expressed in these EBNA2-expressing clones. An increased cell surface expression of CR2 but not of CD23 was observed, and the soluble form of CD23 molecule (SCD23) was released. We were, however, not able to detect any expression of LMP in these cell clones. These data demonstrate that EBNA2 gene is able to complement P3HR1 virus latent functions to induce the activation of CR2 and CD23 expression, and they emphasize the role of EBNA2 protein in the modulation of cellular gene implicated in B-cell proliferation and hence in EBV-mediated B-cell immortalization. Nevertheless, EBNA2 expression in BL/P3HR1 cells is not able to restore the level of CR2 and CD23 expression observed in BL/B95 cells, suggesting that other cellular or viral proteins may also have an important role in the activation of these molecules: the viral LMP seems to be a good candidate.

Antigens, CD↗
PubMed1989

Relationship between nasopharyngeal carcinoma and high antibody titers to Epstein-Barr virus-specific thymidine kinase.

Epstein-Barr virus (EBV) has long been implicated in nasopharyngeal carcinoma (NPC). Recent studies in our and other laboratories have shown a correlation between the disease and high antibody titers to EBV-specific DNase. These data led us to also examine serial sera from healthy adults and patients with infectious mononucleosis or NPC, for their capacity to neutralize the EBV-specific thymidine kinase (TK) activity from chemically induced EBV-carrying human lymphoblastoid cells. Our results were the following: (i) sera were found that efficiently blocked the EBV-specific TK activity of induced-Raji TK- cell extracts, but not the host-cell TK activity from EBV-negative BJAB cells; (ii) a relationship appeared between high levels of EBV-specific TK-neutralizing activity in sera and NPC pathology, even though in this preliminary study the degrees of EBV-induced TK-blocking activity detected in sera were not significantly correlated with EBV-specific antibody titers; (iii) the EBV-induced TK-neutralizing activity was found in the main IgG fraction derived from NPC sera. These data must be compared with other known antibody responses to EBV for their clinical interest in NPC control.

Antibodies↗
PubMed1989

The Epstein-Barr virus (EBV) DR enhancer contains two functionally different domains: domain A is constitutive and cell specific, domain B is transactivated by the EBV early protein R.

The Epstein-Barr virus (EBV) DR promoter is located upstream of the PstI repeats, and besides the TATA box, it contains two cis-acting regulatory elements. One of them has enhancer properties. To define more precisely the functional region(s) in the DR enhancer, we generated 5' and 3' deletion mutants. These deletion mutants, which were transfected into various recipient cells of different origins, allowed us to identify two functionally distinct domains, A and B. Domain A was constitutively active in all cell lines tested, except in lymphoid B cells. Domain B was active in lymphoid B cells, and its activity required both EB1 (the BZLF1-encoded EBV trans-acting factor) and the presence of the EBV genome. This suggested that an EBV-encoded, EB1-inducible factor was activating the enhancer B domain. In effect, the B domain was trans-activated by R, an EBV early product encoded by the open reading frame BRLF1, and the activation by R occurred in epithelial, fibroblastic, and lymphoid cells. The R-responsive element has been reduced to 28 base pairs containing the double palindromic sequence TTGTCCCGTGGACAATGTCC. Both domains A and B act by increasing the initiation of specific RNAs.

Animals↗
PubMed1988

Different patterns of Epstein-Barr virus gene expression and of cytotoxic T-cell recognition in B-cell lines infected with transforming (B95.8) or nontransforming (P3HR1) virus strains.

Epstein-Barr virus (EBV)-negative Burkitt's lymphoma (BL) cell lines have been converted to EBV genome positivity by in vitro infection with the transforming EBV strain B95.8 and with the nontransforming mutant strain P3HR1, which has a deletion in the gene encoding the nuclear antigen EBNA2. These B95.8- and P3HR1-converted lines have been compared for their patterns of expression of EBV latent genes (i.e., those viral genes constitutively expressed in all EBV-transformed lines of normal B-cell origin) and for their recognition by EBV-specific cytotoxic T lymphocytes (CTLs), in an effort to identify which latent gene products provide target antigens for the T-cell response. B95.8-converted lines on several different EBV-negative BL-cell backgrounds all showed detectable expression of the nuclear antigens EBNA1, EBNA2, and EBNA3 and of the latent membrane protein (LMP); such converts were also clearly recognized by EBV-specific CTL preparations with restriction through selected human leukocyte antigen (HLA) class I antigens on the target cell surface. The corresponding P3HR1-converted lines (lacking an EBNA2 gene) expressed EBNA1 and EBNA3 but, surprisingly, showed no detectable LMP; furthermore, these converts were not recognized by EBV-specific CTLs. Such differences in T-cell recognition were not due to any differences in expression of the relevant HLA-restricting determinants between the two types of convert, as shown by binding of specific monoclonal antibodies and by the susceptibility of both B95.8 and P3HR1 converts to allospecific CTLs directed against these same HLA molecules. The results suggest that in the normal infectious cycle, EBNA2 may be required for subsequent expression of LMP and that both EBNA2 and LMP (but not EBNA1 or EBNA3) may provide target antigens for the EBV-specific T-cell response.

Antigens, Viral↗
PubMed1988

Epstein-Barr virus-positive and -negative B-cell lines can be infected with human immunodeficiency virus types 1 and 2.

Human immunodeficiency virus type 1 (HIV-1) can infect CD4+ lymphocytes, monocytes-macrophages, and various other cell lines, including B-cell lines. To study the parameters of B-cell infections, we examined the susceptibility of 24 B-lymphoid cell lines to both HIV-1 and HIV-2 infections. These cell lines included a series of Epstein-Barr virus (EBV) genome-negative Burkitt's lymphoma cell lines and their EBV-converted counterparts. To infect these cells we used two HIV-1 isolates and one HIV-2 isolate. Infections were monitored with a cytoplasmic RNA dot-blot and a syncytium assay. HIV infection was also studied by a novel method based on electrophoresis of DNA liberated from cells that were lysed in situ in the well of an agarose gel. All human B-cell lines could be infected with HIV-1, regardless of the presence of EBV genomes; thus, EBV infection had no major effect on HIV susceptibility of B-cell lines. Integrated proviral HIV genomes could be detected by Southern blot analysis of DNA extracted from long-term, non-HIV-producing B-cell lines. This study suggests that B-lymphoid cells may serve as reservoirs for latent or persistent HIV infections in vivo, even in the absence of EBV infection.

B-Lymphocytes↗
PubMed1987

Epstein-Barr virus (EBV) induces expression of B-cell activation markers on in vitro infection of EBV-negative B-lymphoma cells.

A set of B-cell activation markers, including the EBV/C3d receptor [complement receptor type 2 (CR2) (CD21)], the 45-kDa lymphoblastoid cell-associated (Blast-2) antigen (CD23), and the B-cell restricted activation (Bac-1) antigen (which was recently identified as a potential B-cell growth factor receptor) can be turned on by infecting lymphoma cells that are genome negative for Epstein-Barr virus (EBV) with the B95-8 immortalizing strain of the virus. The nonimmortalizing EBV variant, strain P3HR-1, which possesses a deletion within the BamHI WYH region of the genome containing the coding sequence for the EBV-determined nuclear antigen 2, does not induce expression of these markers. Other lymphoblastoid cell-associated antigen markers can be activated by infection with either immortalizing or nonimmortalizing viruses. These results suggest that the immortalizing potential of EBV is correlated with its ability to induce expression of B-cell activation markers, which are suspected to play a major role in the physiological pathway leading to lymphoid cell proliferation. The viral genomic region deleted in the nonimmortalizing strain of EBV seems to be required for activation of some of these markers. Human lymphoma cell lines, such as those used in this study, can thus help identify the specific EBV genes involved in lymphoid B-cell proliferation and the mechanism of action of these genes.

Antigens, Neoplasm↗
PubMed1986

[Tropical spastic paraparesis in Martinique. High prevalence of anti-HTLV-I antibodies].

Owing to the frequent occurrence in tropical countries of subacute spinal cord diseases of unknown origin, a nosological entity called tropical spastic paraparesis has been individualized. Twenty-two cases have been observed in Martinique. The presence in the serum of antibodies directed against human T-cell leukaemia/lymphoma virus (HTLV-I) in 15 of these 22 patients suggests that this lymphotropic virus or a related one might also be neurovirulent.

Adult↗
PubMed1985

Antibodies to human T-lymphotropic virus type-I in patients with tropical spastic paraparesis.

10 out of 17 (59%) patients with tropical spastic paraparesis (TSP) had antibodies to human T-lymphotropic virus-I (HTLV-I), as did 5 out of 5 TSP patients with systemic symptoms. Only 13 out of 303 (4%) controls, made up of blood donors, medical personnel, and other neurological patients, had such antibodies. These findings suggest either that HTLV-I is neurotropic or that the virus or a related one contributes to the pathogenesis of TSP.

Adolescent↗
PubMed1985

Comparative seroepidemiology of HTLV-I and HTLV-III in the French West Indies and some African countries.

The prevalence of antibodies detected by ELISA against human T-lymphotropic viruses, type I (HTLV-I) and type III (HTLV-III-LAV), is described in a comparative serosurvey in the French West Indies and African countries. The data confirm that the Caribbean basin is endemic for HTLV-I. In this region, HTLV-I antibody prevalence varied from 3.4% to 5.2% among blood donors and increased with age to reach a value of 33% among elderly people from the Dominica Island. In French Guyana, a South American country bordering the Caribbean sea, differences in antibody distribution across three ethnic groups (black Bonis, Indian Wayanas, and Hmongs from Asia) provide clues for investigation of the mode of HTLV-I transmission. Africa appears to be an endemic continent for HTLV-I and HTLV-III. For both viruses, the antibody prevalence exhibited an increasing gradient from northern to equatorial through Sudanic areas. These preliminary data by showing that Africa represents an endemic reservoir of HTLVs and, possibly, of other human retroviruses should stimulate further investigations on the natural history and the geographical origin of these viruses.

Adolescent↗