title: Low ligand requirement for deletion and lack of synapses in positive selection enforce the gauntlet of thymic T cell maturation.
abstract: Immature double-positive (CD4(+)CD8(+)) thymocytes respond to negatively selecting peptide-MHC ligands by forming an immune synapse that sustains contact with the antigen-presenting cell (APC). Using fluorescently labeled peptides, we showed that as few as two agonist ligands could promote APC contact and subsequent apoptosis in reactive thymocytes. Furthermore, we showed that productive signaling for positive selection, as gauged by nuclear translocation of a green fluorescent protein (GFP)-labeled NFATc construct, did not involve formation of a synapse between thymocytes and selecting epithelial cells in reaggregate thymus cultures. Antibody blockade of endogenous positively selecting ligands prevented NFAT nuclear accumulation in such cultures and reversed NFAT accumulation in previously stimulated thymocytes. Together, these data suggest a "gauntlet" model in which thymocytes mature by continually acquiring and reacquiring positively selecting signals without sustained contact with epithelial cells, thereby allowing them to sample many cell surfaces for potentially negatively selecting ligands.
authors.affiliation: Howard Hughes Medical Institute and The Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Peter J R
authors.initials: PJ
authors.lastname: Ebert
authors.forename: Lauren I Richie
authors.initials: LI
authors.lastname: Ehrlich
authors.forename: Mark M
authors.initials: MM
authors.lastname: Davis
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology* / Q000378:metabolism; D017209:Apoptosis; D002467:Cell Nucleus / Q000378:metabolism; D055785:Gene Knockdown Techniques; D054992:Immunological Synapses; D008024:Ligands; D008213:Lymphocyte Activation; D008285:Major Histocompatibility Complex / Q000276:immunology; D051379:Mice; D050778:NFATC Transcription Factors / Q000276:immunology* / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000276:immunology* / Q000378:metabolism; D015398:Signal Transduction; D016176:T-Lymphocyte Subsets / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology / Q000378:metabolism
chemical_list: D008024:Ligands; D050778:NFATC Transcription Factors; D011948:Receptors, Antigen, T-Cell