title: TNF-alpha and IFN-gamma render microglia sensitive to Fas ligand-induced apoptosis by induction of Fas expression and down-regulation of Bcl-2 and Bcl-xL.
abstract: The immune response in the central nervous system (CNS) involves microglial cells which represent intraparenchymal antigen-presenting cells (APC). To control immune effector mechanisms it may be required to induce apoptosis of APC and thereby limit reactivation of T cells that have invaded the CNS. In the present study we investigated the susceptibility of primary murine microglia and of the murine microglial cell line BV-2 to undergo Fas-mediated apoptosis. Whereas resting microglia are resistant to Fas ligand (FasL) treatment, induction of FasL-mediated apoptosis was achieved by treatment with TNF-alpha or IFN-gamma. The effect of these cytokines was paralleled by up-regulation of Fas expression and down-regulation of Bcl-2 and Bcl-xL but not Bax. Activation of microglia by TNF-alpha and IFN-gamma was also accompanied by increased amounts of mRNA for the apoptosis inhibitor FLIP, an effect which did not protect the cells from FasL-induced apoptosis. The FasL-induced cell death pathway in microglia involves reactive oxygen intermediates because the antioxidants N-acetylcysteine and glutathione interfere with induction of apoptosis. Surprisingly, microglia constitutively express FasL on the cell surface. However, blocking of endogenous Fas-FasL interaction with Fas-Fc fusion protein did not enhance the survival of microglia, excluding the possibility of suicide or fratricide mechanisms. By their expression of FasL and their TNF-alpha/IFN-gamma-dependent sensitivity to the pro-apoptotic effect of exogenous FasL, microglial cells may influence the course of T cell-mediated diseases of the CNS.
authors.affiliation: Department of Internal Medicine, University Hospital Zürich, Switzerland.
authors.forename: K S
authors.initials: KS
authors.lastname: Spanaus
authors.forename: R
authors.initials: R
authors.lastname: Schlapbach
authors.forename: A
authors.initials: A
authors.lastname: Fontana
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D002460:Cell Line; D015536:Down-Regulation; D007371:Interferon-gamma / Q000276:immunology* / Q000494:pharmacology; D051379:Mice; D017628:Microglia / Q000276:immunology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000276:immunology*; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology* / Q000494:pharmacology; D015854:Up-Regulation; D051020:bcl-X Protein; D019014:fas Receptor / Q000096:biosynthesis / Q000276:immunology*
chemical_list: C494812:Bcl2l1 protein, mouse; D019253:Proto-Oncogene Proteins c-bcl-2; D014409:Tumor Necrosis Factor-alpha; D051020:bcl-X Protein; D019014:fas Receptor; D007371:Interferon-gamma