Ultraviolet inactivation of Epstein--Barr virus-induced nuclear antigen (EBNA), DNA and IgM synthesis in human B lymphocytes

Activation of B lymphocytes by Epstein-Barr virus/CR2 receptor interaction

Epstein-Barr virus (EBV) infects and transforms human B lymphocytes. The virus receptor was shown to be identical to the complement receptor CR2. The consequences of EBV/CR2 receptor interaction on B lymphocyte activation were analyzed by infection of B cells with the transforming (B95-8) and the nontransforming (P3HR1) virus strains and with UV-inactivated B95-8 virus. Similar to mitogens and antibodies against surface IgM and CR2 receptor, transforming and nontransforming EBV induced the release of leukocyte migration inhibitory factor (LIF). LIF production occurred early after infection and was not affected by irradiation of the B95-8 virus with doses of UV-light which prevented the expression of viral functions. B lymphocytes infected with UV-inactivated virus responded to T cell-derived B cell growth factors. The results demonstrate that binding of EBV to the CR2 receptor activates the B cells. Progression of the infected cells in the activation pathway required helper cell-derived factors or signals provided by the intact viral genome. The nontransforming P3HR1 virus induced a low level of RNA synthesis and increase of cell size and major histocompatibility complex class I antigen expression. Only the transforming virus induced expression of EBV nuclear antigens and cellular DNA synthesis.

Leukocyte migration inhibitory factor production by activated lymphocytes representing immunological memory or virus-receptor interaction: response of T cell subsets to Epstein-Barr virus nuclear antigen, response of B cells to UV inactivated Epstein-Barr virus

Both T and B lymphocytes are known to produce leukocyte migration inhibitory factor (LIF) after appropriate activation. We showed that EBV nuclear antigen (EBNA) triggered T cells for LIF production in an immunologically specific way: only T cells of seropositive individuals responded. Both Fc receptor positive and negative T cells produced LIF, and the presence of macrophages was necessary. The virus itself activated B cells independently of the serological status of the donors, thus the function was not based on immunological memory. This phenomenon was independent of the transforming capacity of the virus, because UV-inactivated virus also elicited LIF production by B lymphocytes. This triggering seems to be the consequence of the virus-receptor interaction on the cell surface.

Secretion of gamma-interferon at the cellular level. Induction by Epstein-Barr virus

Using a haemolytic plaque assay for gamma-interferon (IFN-gamma) secretion we found that in vitro Epstein-Barr virus (EBV) exposure of peripheral blood mononuclear cells from EBV immune individuals led to IFN-gamma secretion, which was apparent within 6 h after virus contact and peaked 12-24 h after induction. Live, ultraviolet-light-irradiated and heat-inactivated virions all caused IFN-gamma secretion. In contrast, blood mononuclear cells from EBV non-immune adults or neonates could not be activated to IFN-gamma production by EBV.

Production of leukocyte migration inhibitory factor (LIF) in human lymphocyte subsets exposed to polyclonal activators

Lymphocyte subsets separated on the basis of nylon-wool adherence and E and EA rosetting, and characterized for the presence of esterase-positive phagocytic cells were investigated for production of leukocyte migration inhibitory factor (LIF) in response to polyclonal T- and B-cell activators, PHA, ConA, PWM, and Epstein-Barr virus (EBV). In the nylon-passed population only the high avidity E+EA+ cells responded to ConA, PHA-induced LIF production in all E-rosetting subsets. The nylon-adherent E+ subset, which contains activated T cells, produced LIF spontaneously. B cells produced LIF when exposed to PWM or uv-inactivated EBV. In accordance with the known T-cell dependence of PWM activation, LIF was detected only in supernatants of reconstituted populations containing both B and T cells. In contrast, uv-inactivated EBV, devoid of transforming potential, elicited LIF production in the pure B-cell population. LIF production in response to polyclonal activators seemed to be independent of accessory cells since reconstitution with autologous macrophages or semipurified monokine, high-molecular-weight Interleukin 1 (IL-1), did not alter the results.