title: Peptide antagonists that promote positive selection are inefficient at T cell activation and thymocyte deletion.
abstract: We set out to determine whether thymocytes from T cell receptor (TCR) transgenic animals specific for a class I-restricted determinant from ovalbumin (OVA) showed the same fine specificity for antigen-driven deletion in single-cell suspension culture as required for mature T cell activation. The transgenic TCR is specific for the Kb-restricted peptide OVA257-264 (SIINFEKL) which is known to have four TCR contact residues at position 1, 4, 6, and 7 from the crystal structure of this fragment in complex with Kb. OVA257-264 analogs systematically substituted at each of these positions were assayed for their ability to promote immature double-positive thymocyte deletion or mature T cell activation of a cytotoxic T lymphocyte line derived from this transgenic mouse. In the absence of additional antigen-presenting cells, single-cell thymocyte suspensions showed that the specificity for double-positive thymocyte deletion and mature T cell activation was virtually identical, demonstrating a limited cross-reactivity with a number of variants having conservative substitutions at these exposed residues. These peptides were considerably more efficient at both thymic deletion and mature T cell activation than a number of non-conservative substitution analogs known to act as antagonists of OVA257-264 and capable of selecting transgenic T cells in thymic organ culture. Therefore, both peripheral T cell activation and thymic deletion have an overall similar pattern of peptide specificity which differs from that required for positive selection. This suggests that a subset of major histocompatibility complex-presented peptides could promote positive selection without causing either thymic deletion or peripheral activation of those selected T cells.
authors.affiliation: Department of Pathology and Immunology, Monash Medical School, Victoria, Australia.
authors.forename: M J
authors.initials: MJ
authors.lastname: Barnden
authors.forename: W R
authors.initials: WR
authors.lastname: Heath
authors.forename: S
authors.initials: S
authors.lastname: Rodda
authors.forename: F R
authors.initials: FR
authors.lastname: Carbone
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017637:Clonal Deletion; D003602:Cytotoxicity, Immunologic; D008213:Lymphocyte Activation; D008212:Lymphocyte Depletion; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D010047:Ovalbumin / Q000737:chemistry / Q000276:immunology; D010455:Peptides / Q000737:chemistry / Q000276:immunology*; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000276:immunology*; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D013950:Thymus Gland / Q000166:cytology
chemical_list: D010455:Peptides; D016693:Receptors, Antigen, T-Cell, alpha-beta; D010047:Ovalbumin