title: Direct observation of ligand recognition by T cells.
abstract: The activation of T cells through interaction of their T-cell receptors with antigenic peptide bound to major histocompatibility complex (MHC) on the surface of antigen presenting cells (APCs) is a crucial step in adaptive immunity. Here we use three-dimensional fluorescence microscopy to visualize individual peptide-I-E(k) class II MHC complexes labelled with the phycobiliprotein phycoerythrin in an effort to characterize T-cell sensitivity and the requirements for forming an immunological synapse in single cells. We show that T cells expressing the CD4 antigen respond with transient calcium signalling to even a single agonist peptide-MHC ligand, and that the organization of molecules in the contact zone of the T cell and APC takes on the characteristics of an immunological synapse when only about ten agonists are present. This sensitivity is highly dependent on CD4, because blocking this molecule with antibodies renders T cells unable to detect less than about 30 ligands.
authors.affiliation: Department of Microbiology & Immunology and The Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California 94305, USA.
authors.forename: Darrell J
authors.initials: DJ
authors.lastname: Irvine
authors.forename: Marco A
authors.initials: MA
authors.lastname: Purbhoo
authors.forename: Michelle
authors.initials: M
authors.lastname: Krogsgaard
authors.forename: Mark M
authors.initials: MM
authors.lastname: Davis
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D000938:Antigen-Presenting Cells / Q000276:immunology / Q000378:metabolism; D000941:Antigens / Q000276:immunology*; D015704:CD4 Antigens / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D004306:Dose-Response Relationship, Immunologic; D000949:Histocompatibility Antigens Class II / Q000276:immunology* / Q000378:metabolism; D008024:Ligands; D051379:Mice; D008822:Mice, Transgenic; D010455:Peptides / Q000276:immunology
chemical_list: D000941:Antigens; D015704:CD4 Antigens; D000949:Histocompatibility Antigens Class II; D008024:Ligands; D010455:Peptides; D002118:Calcium