title: Cathepsin-dependent apoptosis triggered by supraoptimal activation of T lymphocytes: a possible mechanism of high dose tolerance.
abstract: High doses of Ag can paradoxically suppress immune responses in vivo. This Ag-specific unresponsiveness (termed high dose tolerance) involves extrathymic mechanisms in mature T lymphocytes. To investigate these mechanisms, we used the in vitro model of PBL activated with anti-CD3 or PHA. In these conditions, increasing mitogen concentrations resulted in a reduction of the proliferative response, associated with an increased percentage of apoptotic cells. Apoptosis did not require prior exposure to IL-2, it was not the consequence of CD178/CD95 or TNF/TNFR interactions, and was therefore clearly distinct from activation-induced cell death. Although the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD-fmk) decreased DNA fragmentation, cytochrome c release and caspase-9 and caspase-3 activation were not implicated, suggesting that this apoptosis did not primarily involve the intrinsic mitochondrial pathway. E64d, a cysteine protease inhibitor, as well as specific inhibitors of cathepsin B and cathepsin L conferred protection. We further demonstrated that cathepsin B and cathepsin L were released from the lysosomes and catalytically active in the cytosol. Release of cathepsin B and cathepsin L was the consequence of lysosomal membrane permeabilization without complete disruption of the cytosol-lysosome pH gradient. These results demonstrate a role for cathepsins in supraoptimal activation-induced apoptosis in vitro and suggest their possible participation in high dose tolerance in vivo.
authors.affiliation: Laboratoire d'Immunopharmacologie, Institut National de la Santé et de la Recherche Médicale Unité 503, Centre d'Etudes et de Recherche en Virologie et Immunologie, Lyon, France.
authors.forename: Marie-Cécile
authors.initials: MC
authors.lastname: Michallet
authors.forename: Frédéric
authors.initials: F
authors.lastname: Saltel
authors.forename: Monique
authors.initials: M
authors.lastname: Flacher
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Revillard
authors.forename: Laurent
authors.initials: L
authors.lastname: Genestier
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000276:immunology*; D018106:CD28 Antigens / Q000494:pharmacology; D061945:Caspase Inhibitors; D002384:Catalysis; D002401:Cathepsin B / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D056668:Cathepsin L; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D016923:Cell Death / Q000276:immunology; D002454:Cell Differentiation / Q000276:immunology; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects / Q000276:immunology; D004306:Dose-Response Relationship, Immunologic; D016193:G1 Phase / Q000276:immunology; D006801:Humans; D007425:Intracellular Membranes / Q000201:enzymology / Q000276:immunology; D008213:Lymphocyte Activation / Q000276:immunology*; D008247:Lysosomes / Q000201:enzymology; D016853:Muromonab-CD3 / Q000494:pharmacology; D010539:Permeability; D016196:S Phase / Q000276:immunology; D013601:T-Lymphocytes / Q000166:cytology / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D018106:CD28 Antigens; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D016853:Muromonab-CD3; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D045304:Cytochromes c; D002403:Cathepsins; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; C534281:CTSL protein, human; D056668:Cathepsin L; D013755:Tetradecanoylphorbol Acetate