title: Constitutive caspase activation and impaired death-inducing signaling complex formation in CD95-resistant, long-term activated, antigen-specific T cells.
abstract: Elimination of T cells during an immune response is mediated by activation-induced cell death (AICD) and CD95-mediated apoptosis. Chronic graft-vs-host disease and T cell-mediated autoimmune diseases are caused by the persistence of activated T cells that escaped tolerance induction by deletion or silencing. To mimic the in vivo situation of long-term activated T cells, we generated an in vitro system using HLA-A1-specific T cells, weekly restimulated by Ag. While short-term activated T cells (two to five rounds of stimulation) were CD95 sensitive and susceptible to AICD, T cells stimulated more than eight times acquired constitutive CD95 resistance and exhibited reduced AICD. Phenotypically, these long-term activated T cells could be identified as effector/memory T cells. The expression of the proforms of the CD95 receptor initiator caspases, caspase-8 and -10, and the effector caspase-3 was strongly decreased in these cells, and only active caspase fragments were detected. In contrast to short-term activated T cells, constitutive CD95 receptor clustering was observed on the cell surface, and caspase-8 was bound to the CD95 receptor in the absence of receptor triggering. After further cross-linking of CD95, additional formation of the death-inducing signaling complex (DISC) was strongly impaired. Reduced DISC formation in long-term activated T cells was associated with the loss of PTEN expression and the increased phosphorylation of protein kinase B. Inhibitors of phosphoinositol 3-kinase restored CD95 sensitivity and DISC formation in long-term activated T cells. These data suggest that defective CD95 signaling in effector/memory T cells may contribute to the apoptosis resistance toward physiological stimuli in T cells mediating tissue destruction in vivo.
authors.affiliation: University Children's Hospital and Institute of Pathology, University of Ulm, Ulm, Germany.
authors.forename: Gudrun
authors.initials: G
authors.lastname: Strauss
authors.forename: Ingrid
authors.initials: I
authors.lastname: Knape
authors.forename: Ingo
authors.initials: I
authors.lastname: Melzner
authors.forename: Klaus-Michael
authors.initials: KM
authors.lastname: Debatin
mesh_terms: D017209:Apoptosis / Q000276:immunology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D002352:Carrier Proteins / Q000096:biosynthesis / Q000502:physiology; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D016923:Cell Death / Q000276:immunology; D002460:Cell Line; D002461:Cell Line, Transformed; D053418:Death Domain Receptor Signaling Adaptor Proteins; D015536:Down-Regulation / Q000276:immunology; D004789:Enzyme Activation / Q000276:immunology; D018984:Epitopes, T-Lymphocyte / Q000276:immunology; D053222:Fas Ligand Protein; D015788:HLA-A1 Antigen / Q000276:immunology; D006801:Humans; D007113:Immunity, Innate; D007156:Immunologic Memory; D016130:Immunophenotyping; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D008213:Lymphocyte Activation / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000032:analysis; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D010766:Phosphorylation; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011506:Proteins / Q000502:physiology; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000276:immunology*; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D013997:Time Factors; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D015854:Up-Regulation / Q000276:immunology; D051636:X-Linked Inhibitor of Apoptosis Protein; D019014:fas Receptor / Q000032:analysis / Q000378:metabolism / Q000502:physiology*
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins; D061945:Caspase Inhibitors; D020169:Caspases; D053418:Death Domain Receptor Signaling Adaptor Proteins; D018984:Epitopes, T-Lymphocyte; D053222:Fas Ligand Protein; D015788:HLA-A1 Antigen; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D008562:Membrane Glycoproteins; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D010744:Phosphoric Monoester Hydrolases; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D018124:Receptors, Tumor Necrosis Factor; D025521:Tumor Suppressor Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; D019014:fas Receptor; C506386:CFLAR protein, human; C505661:FASLG protein, human; C496866:XIAP protein, human; C494929:PTEN protein, human