RESUMO
T cells specific for the cytochrome c Ag are widely used to investigate many aspects of TCR specificity and interactions with peptide-MHC, but structural information has long been elusive. In this study, we present structures for the well-studied 2B4 TCR, as well as a naturally occurring variant of the 5c.c7 TCR, 226, which is cross-reactive with more than half of possible substitutions at all three TCR-sensitive residues on the peptide Ag. These structures alone and in complex with peptide-MHC ligands allow us to reassess many prior mutagenesis results. In addition, the structure of 226 bound to one peptide variant, p5E, shows major changes in the CDR3 contacts compared with wild-type, yet the TCR V-region contacts with MHC are conserved. These and other data illustrate the ability of TCRs to accommodate large variations in CDR3 structure and peptide contacts within the constraints of highly conserved TCR-MHC interactions.
Assuntos
Linfócitos T CD4-Positivos/imunologia , Citocromos c/imunologia , Receptores de Antígenos de Linfócitos T/imunologia , Animais , Antígenos CD/química , Antígenos CD/imunologia , Antígenos CD/metabolismo , Regiões Determinantes de Complementaridade/química , Regiões Determinantes de Complementaridade/imunologia , Reações Cruzadas , Cristalografia por Raios X , Citocromos c/metabolismo , Humanos , Ligantes , Camundongos , Modelos Moleculares , Ligação Proteica , Estrutura Terciária de Proteína , Receptores de Antígenos de Linfócitos T/química , Receptores de Antígenos de Linfócitos T/metabolismo , Receptores Imunológicos/química , Receptores Imunológicos/imunologia , Receptores Imunológicos/metabolismo , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/imunologia , Proteínas Recombinantes de Fusão/metabolismo , Família de Moléculas de Sinalização da Ativação Linfocitária , Ressonância de Plasmônio de SuperfícieRESUMO
Self-peptide MHCII ligands are critical for selection of CD4+ T cells in the thymus, and maintenance in the periphery. To date, no investigation as to the exact thymic and peripheral expression of a naturally occurring positive selecting self-peptide MHCII (self-pMHCII) complex has taken place. We have generated a sensitive T cell hybridoma to functionally detect the endogenous presentation of a confirmed positive selecting self-pMHCII complex for a CD4+ transgenic T cell. Using this tool to survey and quantify the expression selecting of self-pMHCII, we have shown unequivocal proof that a known CD4+ selecting ligand can be presented on both positive and negative selecting thymic APCs. We also show that peripheral presentation of this same selecting ligand is affected by the activation state of the APCs. Furthermore, discrepancies between the gene expression and self-pMHCII complex presentation of this bona fide selecting ligand suggest that functional detection self-ligand complexes will be required to establish a complete view of the naturally presented endogenous self-pMHC landscape.