Establishment of spontaneously outgrowing lymphoblastoid cell lines with Cyclosporin A

Exosomes derived from Epstein-Barr virus-infected cells are internalized via caveola-dependent endocytosis and promote phenotypic modulation in target cells

Epstein-Barr virus (EBV), a human gammaherpesvirus, establishes a lifelong latent infection in B lymphocytes and epithelial cells following primary infection. Several lines of evidence suggest that exosomes derived from EBV-infected cells are internalized and transfer viral factors, including EBV-encoded latent membrane protein and microRNAs, to the recipient cells. However, the detailed mechanism by which exosomes are internalized and their physiological impact on the recipient cells are still poorly understood. In this study, we visualized the internalization of fluorescently labeled exosomes derived from EBV-uninfected and EBV-infected B cells of type I and type III latency into EBV-negative epithelial cells. In this way, we demonstrated that exosomes derived from all three cell types were internalized into the target cells in a similar fashion. Internalization of exosomes was significantly suppressed by treatment with an inhibitor of dynamin and also by the knockdown of caveolin-1. Labeled exosomes were colocalized with caveolae and subsequently trafficked through endocytic pathways. Moreover, we observed that exosomes derived from type III latency cells upregulated proliferation and expression of intercellular adhesion molecule 1 (ICAM-1) in the recipient cells more significantly than did those derived from EBV-negative and type I latency cells. We also identified the EBV latent membrane protein 1 (LMP1) gene as responsible for induction of ICAM-1 expression. Taken together, our data indicate that exosomes released from EBV-infected B cells are internalized via caveola-dependent endocytosis, which, in turn, contributes to phenotypic changes in the recipient cells through transferring one or more viral factors.

Molecular virology of Epstein-Barr virus

Epstein-Barr virus (EBV) interacts with its host in three distinct ways in a highly regulated fashion: (i) EBV infects human B lymphocytes and induces proliferation of the infected cells, (ii) it enters into a latent phase in vivo that follows the proliferative phase, and (iii) it can be reactivated giving rise to the production of infectious progeny for reinfection of cells of the same type or transmission of the virus to another individual. In healthy people, these processes take place simultaneously in different anatomical and functional compartments and are linked to each other in a highly dynamic steady-state equilibrium. The development of a genetic system has paved the way for the dissection of those processes at a molecular level that can be studied in vitro, i.e. B-cell immortalization and the lytic cycle leading to production of infectious progeny. Polymerase chain reaction analyses coupled to fluorescent-activated cell sorting has on the other hand allowed a descriptive analysis of the virus-host interaction in peripheral blood cells as well as in tonsillar B cells in vivo. This paper is aimed at compiling our present knowledge on the process of B-cell immortalization in vitro as well as in vivo latency, and attempts to integrate this knowledge into the framework of the viral life cycle in vivo.

Mosaicicm in bcr-abl protein expression in B cells in chronic myelogenous leukemia

Chronic myelogenous leukemia is a disease of the pluripotent stem cell that involves the myeloid and, to a varying degree, the lymphoid compartment. We studied the involvement of B cells in chronic myelogenous leukemia at diagnosis and during treatment. B lymphocytes were immortalized by infection with Epstein-Barr virus. B-lymphoid cell lines could be established from 25 patients suffering from Philadelphia-chromosome (Ph1)-positive chronic myelogenous leukemia. The cell lines were tested for expression of the typical 210-kDa fusion protein, p210, using Western-blot analysis, and/or for mRNA expression of bcr-abl fusion genes, using reverse transcriptase polymerase chain reaction analysis. At diagnosis, mosaicism of B cells was demonstrated in every patient. During treatment with interferon alpha, p210-expressing B-lymphoid cell lines could not be established from 8 of 8 patients. Following discontinuation of IFN-alpha therapy, p210-positive cell lines were found early, even before cytogenetic recurrence. Resistance to IFN-alpha therapy and progression of the disease were both associated with the appearance of p210-positive cell lines. Cell lines established from 3 healthy individuals and from patients suffering from Ph1-negative diseases did not show p210 expression in Western blots. Our data suggest that B lymphocytes are involved early in the disease, and that B-cell mosaicism may be a sensitive marker for resistance to IFN-alpha therapy and disease progression.

An Epstein-Barr virus-associated superantigen

More than 90% of adults are latently infected with Epstein-Barr virus (EBV), the causative agent of infectious mononucleosis, a self-limiting lymphoproliferative disease characterized by extensive T cell activation. Reactivation of this herpesvirus during immunosuppression is often associated with oncogenesis. These considerations led us to analyze the early events that occur after exposure of the immune system to EBV. Strong major histocompatibility complex (MHC) class II-dependent but not MHC-restricted, T cell proliferation was observed in vitro in response to autologous, lytically infected EBV-transformed B cells. By measuring the appearance of the early activation marker CD69 on individual T cell V beta subsets, we could demonstrate selective activation of human V beta 13- T cells. This was confirmed with murine T cell hybridomas expressing various human BV genes. While EBV- Burkitt's lymphoma cells were nonstimulatory, they induced V beta-restricted T cell activation after EBV infection. EBV specific activation was also demonstrated in cord blood cells, excluding a recall-antigen response. Thus, all of the characteristics of a superantigen-stimulated response are seen, indicating that induction of the EBV lytic cycle is associated with the expression of a superantigen in B cells. A model is presented proposing a role for the superantigen in infection, latency, and oncogenesis.

Glycosylphosphatidylinositol (GPI)-anchored surface antigens in the allogeneic activation of T cells

GPI-linked surface molecules have recently been described as structures with an activation potential for human T lymphocytes. To study the role of these molecules in T cell activation we analysed GPI-deficient or normal T cells from patients with paroxysmal nocturnal haemoglobinuria (PNH). On activation with allogeneic Epstein-Barr virus (EBV)-transformed B cell lines GPI-deficient freshly separated T cells or continuously growing T cell lines exhibited a significantly lower proliferation or cytokine production compared with their normal counterparts. In contrast, stimulation via the T cell receptor-associated CD3 structure resulted in a comparable response. There was no difference in activation of normal T lymphocytes when GPI-deficient B cells were used as stimulators compared with normal B cells obtained from the same PNH patient. We conclude from these data that GPI deficiency in PNH leads to a functional deficiency of GPI-deficient T cells. In contrast, no difference in activation of T lymphocytes for GPI-deficient cells on the stimulator cell level was observed.

Plasmodium falciparum-inhibitory monoclonal antibodies produced by human hybridomas

Stable human hybridomas were generated that produced inhibitory anti-Plasmodium falciparum monoclonal antibodies. Peripheral blood lymphocytes, obtained from adults in Liberia, a malaria endemic area, were immortalized with Epstein-Barr virus and then fused with KR4, a human, lymphoblastoid cell line. Stable hybridomas that produced anti-P. falciparum monoclonal antibody were identified by an ELISA assay that used the trophozoite and schizont antigens of both the Honduras I and FCR3 parasite strains. Monoclonal antibodies produced by selected hybridomas derived from lymphocytes of two individuals were subsequently studied. The anti-parasite antibodies were produced at 1-3 micrograms/ml in culture supernatants. All of the monoclonal antibodies bound specifically to trophozoites and schizonts of both strains of parasite in an indirect immunofluorescence assay and inhibited production of ring stage parasites by more than 90% when added to trophozoite or schizont containing erythrocytes in culture. Western immunoblot analysis of antigens obtained from trophozoites and schizonts (parasite age span of 36 to 48 h) was performed using either affinity purified or ammonium sulfate-concentrated monoclonal antibody. Antibody from three hybridomas which bound primarily to antigens of the Honduras 1 strain had Mr of approximately 140,000, 130,000 and 123,000.