Showing papers by "Guido Kroemer published in 1994"

Differential in vivo effects of a superantigen and an antibody targeted to the same T cell receptor. Activation-induced cell death vs passive macrophage-dependent deletion.

Abstract: Superantigens have multiple pleiotropic effects in vivo, causing the activation, proliferation, and deletion of specific T cells. In our study, we analyzed the effects of the bacterial superantigen Staphylococcus aureus enterotoxin B (SEB) on peripheral T cells in vivo. As an internal control we took advantage of a IgG2a mAb, F23.1 (anti-V beta 8), that recognizes products from the same V beta gene family as that recognized by SEB. Suprisingly, not only SEB, but also F23.1 primes peripheral T cells to undergo oligonucleosomal DNA fragmentation typical for programmed cell death (PCD). Nonetheless the deletion and induction of PCD imposed by both agents obey rather different principles. First, SEB, not F23.1-induced PCD, concerns T cells that have passed through the S phase of the cell cycle, as demonstrated by experiments in which the thymidine analogue 5-bromo-2'desoxyuridine was detected in mono- and oligonucleosomal fragments of T cells undergoing PCD. Second, deletion of V beta 8+ T cells induced by SEB, not F23.1, can be blocked in vivo by high doses of retinol and, during the early phase, by glucocorticoid receptor blockade with RU-38486. Inasmuch as retinol fails to antagonize the glucocorticoid-induced PCD, at least two pathways are involved in early SEB-driven deletion, one that depends on the presence of endogenous glucocorticoid, and another that can be inhibited by retinol. Third, depletion of phagocytes in vivo by means of liposome-encapsulated dichloromethylene diphosphonate does not impede the activation and deletion of V beta 8+ cells by SEB, although it partially prevents the elimination of T cells binding F23.1 in vivo. Thus, macrophages are not rate-limiting for the action of SEB. In a further series of experiments, we demonstrate that SEB causes the secretion of a variety of cytokines (IL-1, -2, -4, -10, granulocyte-macrophage-CSF, IFN-gamma, and TNF) that may cause lethal septic shock. In contrast, F23.1 that efficiently induces all these mediators in vitro, fails to do so in vivo. In synthesis, the elimination of T cells induced by two different agents specific for V beta 8 obeys different principles: activation-induced cell death in the case of SEB and passive macrophage-mediated elimination in the case of F23.1.

Linomide inhibits programmed cell death of peripheral T cells in vivo.

Abstract: Programmed cell death (PCD) is involved in the physiological regulation of lymphocyte turnover, as well in the antigen-driven selection of T and B cells. Here it is shown that the immunomodulator linomide (quinoline-3-carboxamide) inhibits the apoptotic decay of peripheral T lymphocytes in response to three different stimuli. First, linomide reduces the superantigen-mediated apoptosis and deletion of specific T lymphocytes of both the CD4+ and the CD8+ subsets without affecting other superantigen-triggered phenomena such as T cell expansion and anergy. Second, linomide abolishes the T lymphopenia and inhibits PCD of splenic CD4+ and CD8+ T cells induced by exogenous glucocorticoids. This effect is restricted to peripheral T lymphocytes and does not concern thymocytes. Finally, linomide abolishes the development of lymphopenia that follows infection with vaccinia virus, while reducing PCD of CD4+ and CD8+ peripheral T cells. The anti-apoptotic effect of linomide could account for its immunostimulatory properties and might be relevant to the treatment of immunodeficiencies associated with an increased apoptotic decay of T lymphocytes.

Pertussis toxin interferes with superantigen-induced deletion of peripheral T cells without affecting T cell activation in vivo. Inhibition of deletion and associated programmed cell death depends on ADP-ribosyltransferase activity.

Abstract: Intravenous injection of a bacterial superantigen such as Staphylococcus aureus enterotoxin B (SEB) causes transient activation and expansion of SEB-reactive V beta 8+ T cells, as well as specific down-regulation of the immune response, through partial deletion of superantigen-reactive T cells. Here we demonstrate that co-administration of pertussis toxin (PTX) and SEB reduces the SEB-induced deletion of V beta 8+ T cells, although it does not affect T cell activation and proliferation. PTX abrogates the SEB-driven deletion of V beta 8+CD4+ (not V beta 8+CD8+) splenocytes that is observed early (12-24 h) after SEB injection. Moreover, it antagonizes the late (> or = 4 days) deletion of V beta 8+CD4+ and V beta 8+CD8+ peripheral T cells that follows transient expansion of such cells. This phenomenon is associated with significant reductions in apoptosis and endonucleolysis and is not caused by a compensatory increase in proliferation of SEB-reactive T cells, as we determined by using a combined fluorometric analysis of cell cycle and DNA alterations, which are associated with programmed cell death. These effects are also observed in thymectomized animals, thus excluding the possibility that PTX might act by enhancing the maturation and export of thymic T cells to the periphery. Moreover, the SEB-induced reduction of V beta 8+ splenocytes is antagonized by PTX in vitro. The capacity of PTX to reduce clonal deletion depends critically on its ADP-ribosyltransferase activity, inasmuch as a non-enzymatic PTX mutant fails to act in this biologic system. We conclude that PTX selectively antagonizes or impedes the delivery of negative signals to T cells, which are stimulated by superantigens, without interfering with the transmission of stimulatory signals.

Pertussis toxin inhibits activation-induced cell death of human thymocytes, pre-B leukemia cells and monocytes.

Abstract: Activation of human thymocytes and pre-B cells via the CD3/T cell receptor (TCR) complex or the IgM/B cell receptor complex, respectively, results in apoptotic cell death. Similarly, cross-linking of the activation marker CD69, which belongs to the natural killer complex, causes apoptosis of lipopolysaccharide-preactivated monocytes. Here we show that pertussis toxin (PTX) inhibits the activation-induced apoptosis of these three cell types, though it fails to prevent the programmed cell death that follows exposure of cells to the synthetic glucocorticoid dexamethasone (thymocytes, pre-B cells) or to interleukin 4 (monocytes). The capacity of pertussis toxin to suppress activation-induced death is not due to quenching of the activation signal, because thymocytes exposed to PTX are still capable of mobilizing Ca2+ after TCR-alpha/beta cross-linking and proliferate in response to costimulation with PTX and CD3/TCR ligation. The apoptosis-inhibitory effect of PTX depends on the presence of an intact adenosine diphosphate (ADP)-ribosylating moiety, since a mutant pertussis toxin molecule that lacks enzymatic activity, but still possesses the membrane translocating activity, fails to interfere with activation-induced cell death. A toxin that induces a different spectrum of ADP ribosylation than PTX, cholera toxin, fails to inhibit apoptosis. To suppress apoptosis, the intact PTX holotoxin must be added to cells before the lethal activation step; its addition 30 min after initial activation remains without effect on apoptosis. These data unravel a PTX sensitive signal transduction event that intervenes during an early step of activation-induced cell death of immune cells.