title: Noncytotoxic human CD4+ T-cell clones presenting and simultaneously responding to an antigen die of apoptosis.
abstract: Activated T-cells expressing MHC class II surface antigens are able to present antigen and thus function as peptide-presenting cells (T-APCs). In this study we investigated whether antigen presentation by T-cells induced programmed cell death. As a model we used tetanus p30 peptide (aa 947-967)-specific, noncytotoxic CD4+ T-cell clones (C11 and C31). For experimental purposes these T-cell clones were stimulated (a) with p30 peptide-pulsed and fixed EBV-transformed antigen-presenting cells (B-APCs), (b) with p30-pulsed and fixed activated T-cells as APCs (as T-APCs we used either the T-cell clones themselves or an autologous T-cell clone (CT3) with p30 unrelated specificity), or (c) with soluble p30 peptide. The efficiency of antigen presentation was monitored by measuring proliferation as [3H]thymidine uptake. Apoptosis was measured by quantifying fragmented, cytoplasm DNA with the fluorescent dye 4,6-diamidino-2-phenylindole or by visualizing fragmented DNA by gel electrophoresis. Stimulation with p30-pulsed and fixed B-APCs or T-APCs induced proliferation but no apoptosis of the responding T-cells. However, stimulation of cloned T-cells with soluble peptide induced up-regulation of the FAS surface molecules and apoptosis, which was dependent on the peptide doses. Because cloned T-cells express HLA class II molecules, they can theoretically exert both functions at once: antigen presentation and antigen response when they are stimulated with soluble peptide. Because death by apoptosis is only seen under such circumstances, we suggest that T-cells simultaneously presenting and responding to an antigen die of apoptosis and thus contribute to the down-regulation of the immune response. Such phenomena might occur in HIV infection when activated CD4+ T-cells take up gp120 via their CD4 molecules, present it on their HLA class II surface antigens, and are simultaneously stimulated via their TCR.
authors.affiliation: Institute for Immunology and Allergology, Inselspital, Bern, Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Bettens
authors.forename: E
authors.initials: E
authors.lastname: Frei
authors.forename: K
authors.initials: K
authors.lastname: Frutig
authors.forename: D
authors.initials: D
authors.lastname: Mauri
authors.forename: W J
authors.initials: WJ
authors.lastname: Pichler
authors.forename: T
authors.initials: T
authors.lastname: Wyss-Coray
mesh_terms: D000938:Antigen-Presenting Cells / Q000276:immunology*; D000954:Antigens, Surface / Q000096:biosynthesis; D017209:Apoptosis; D001402:B-Lymphocytes / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D002999:Clone Cells; D004305:Dose-Response Relationship, Drug; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis; D006801:Humans; D008213:Lymphocyte Activation / Q000276:immunology*; D010446:Peptide Fragments / Q000276:immunology / Q000633:toxicity; D013744:Tetanus Toxin / Q000276:immunology / Q000633:toxicity; D019014:fas Receptor
chemical_list: D000954:Antigens, Surface; D000949:Histocompatibility Antigens Class II; C091828:P30 tetanus toxin peptide; D010446:Peptide Fragments; D013744:Tetanus Toxin; D019014:fas Receptor