title: Involvement of apoptosis antigen Fas in clonal deletion of human thymocytes.
abstract: Apoptosis appears to play a major role in the differentiation and selection of T and B lymphocytes, but the mechanisms of clonal deletion of T cells in thymus are not well understood. We have prepared an anti-human Fas IgM mAb with associated apoptosis-inducing activity in Fas antigen-positive target cells including human T cells. We analyzed the expression of apoptosis antigen Fas on human thymocytes by cytofluorometry showing low, but significant amounts of Fas antigen on double-negative and double-positive undifferentiated thymocytes. On the contrary, most of the differentiated thymocytes (single-positive or CD3-brightest) expressed undetectable levels of Fas antigen. About 1-2% of thymocytes expressed high amounts of Fas antigen, and these cells, which were CD3-bright, were CD4-bright and CD8-low at the stage of late double-positive lineage. Immunohistological analysis shows these Fas-bright cells on the edge of the medulla. Stimulation through the TCR complex was shown to induce the expression of Fas antigen on thymocytes at the late double-positive stage and prolonged stimulation through the TCR complex rendered the Fas-bright thymocytes sensitive to apoptosis-inducing activity of anti-Fas. To show the involvement of the Fas system in the negative selection/clonal deletion of thymocytes, we organ-cultured human thymus in the presence of the superantigen, staphylococcus enterotoxin B (SEB), and new antagonistic anti-Fas mAb, which can inhibit the apoptosis-inducing activity of the original anti-Fas mAb. The SEB-reactive TCR complex on thymocytes was at first down-regulated by SEB, then the SEB-reactive clone was deleted by apoptosis, which was inhibited by an antagonistic anti-Fas mAb. Thus, Fas antigen is shown to be involved in the negative selection/clonal deletion of superantigen-reactive thymocytes.
authors.affiliation: Pharmaceutical Basic Research Laboratories, JT Inc., Yokohama, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Yonehara
authors.forename: Y
authors.initials: Y
authors.lastname: Nishimura
authors.forename: S
authors.initials: S
authors.lastname: Kishil
authors.forename: M
authors.initials: M
authors.lastname: Yonehara
authors.forename: K
authors.initials: K
authors.lastname: Takazawa
authors.forename: T
authors.initials: T
authors.lastname: Tamatani
authors.forename: A
authors.initials: A
authors.lastname: Ishii
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D000954:Antigens, Surface / Q000096:biosynthesis / Q000276:immunology*; D017209:Apoptosis / Q000276:immunology; D002675:Child, Preschool; D017637:Clonal Deletion / Q000276:immunology*; D004768:Enterotoxins / Q000276:immunology; D005434:Flow Cytometry; D006801:Humans; D007124:Immunoenzyme Techniques; D009924:Organ Culture Techniques; D018089:Superantigens / Q000276:immunology; D013950:Thymus Gland / Q000166:cytology*; D019014:fas Receptor
chemical_list: D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; D004768:Enterotoxins; D018089:Superantigens; D019014:fas Receptor; C031818:enterotoxin B, staphylococcal