title: The apoptotic protease-activating factor 1-mediated pathway of apoptosis is dispensable for negative selection of thymocytes.
abstract: Negative selection is a process to delete potentially autoreactive clones in developing thymocytes. Programmed cell death or apoptosis is thought to play an important role in this selection process. In this study, we investigated the role of apoptotic protease-activating factor 1 (Apaf1), a mammalian homologue of CED-4, in programmed cell death during the negative selection in thymus. There was no developmental abnormality in thymocytes from newborn Apaf1(-/-) mice in terms of CD4 and CD8 expression pattern and thymocyte number. Clonal deletion by endogenous male H-Y Ag of Apaf1-deficient thymocytes with transgenic expression of H-Y Ag-specific TCRs (H-Y Tg/Apaf1(-/-) thymocytes) was normally observed in lethally irradiated wild-type mice reconstituted with fetal liver-derived hemopoietic stem cells. Clonal deletion induced in vitro by a bacterial superantigen was also normal in fetal thymic organ culture. Thus, Apaf1-mediated pathway of apoptosis is dispensable for the negative selection of thymocytes. However, H-Y Tg/Apaf1(-/-) thymocytes showed partial resistance to H-Y peptide-induced deletion in vitro as compared with H-Y Tg/Apaf1(+/-) thymocytes, implicating the Apaf1-mediated apoptotic pathway in the negative selection in a certain situation. In addition, the peptide-induced deletion was still observed in H-Y Tg/Apaf1(-/-) thymocytes in the presence of a broad spectrum caspase inhibitor, z-VAD-fmk, suggesting the presence of caspase-independent cell death pathway playing roles during the negative selection. We assume that mechanisms for the negative selection are composed of several cell death pathways to avoid failure of elimination of autoreactive clones.
authors.affiliation: Department of Immunology and Technical Support Laboratory, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
authors.forename: Hiromitsu
authors.initials: H
authors.lastname: Hara
authors.forename: Atsunobu
authors.initials: A
authors.lastname: Takeda
authors.forename: Michiyo
authors.initials: M
authors.lastname: Takeuchi
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Wakeham
authors.forename: Annick
authors.initials: A
authors.lastname: Itié
authors.forename: Masafumi
authors.initials: M
authors.lastname: Sasaki
authors.forename: Tak W
authors.initials: TW
authors.lastname: Mak
authors.forename: Akihiko
authors.initials: A
authors.lastname: Yoshimura
authors.forename: Kikuo
authors.initials: K
authors.lastname: Nomoto
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yoshida
mesh_terms: D000818:Animals; D017209:Apoptosis; D053477:Apoptotic Protease-Activating Factor 1; D002478:Cells, Cultured; D002678:Chimera; D017637:Clonal Deletion; D004768:Enterotoxins / Q000276:immunology; D005260:Female; D019672:Genes, T-Cell Receptor; D006182:H-Y Antigen / Q000276:immunology; D018380:Hematopoietic Stem Cell Transplantation; D008099:Liver / Q000196:embryology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009924:Organ Culture Techniques; D011506:Proteins / Q000235:genetics / Q000502:physiology*; D017634:Self Tolerance; D015398:Signal Transduction; D018089:Superantigens / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D013950:Thymus Gland / Q000276:immunology*
chemical_list: C506593:Apaf1 protein, mouse; D053477:Apoptotic Protease-Activating Factor 1; D004768:Enterotoxins; D006182:H-Y Antigen; D011506:Proteins; D018089:Superantigens; C031818:enterotoxin B, staphylococcal