Weak agonist self‐peptides promote selection and tuning of virus‐specific T cells

Abstract

Recent progress has begun to define the interactions and signaling pathways that are triggered during positive selection. To identify and further examine self-peptides that can mediate positive selection, we searched a protein-database to find peptides that have minimal homology with the viral peptide (p33) that activates a defined P14 transgenic TCR. We identified four peptides that could bind the restriction element H-2D b and induce proliferation of P14 transgenic splenocytes at high concentration. Two of the four peptides (DBM and RPP) were able to positively select the virus-specific TCR in fetal thymic organ culture but were unable to induce clonal deletion. Reverse-phase HPLC and mass spectrometry demonstrated that these peptides were presented by H-2D b molecules on thymic epithelial cell lines. We also examined whether the selecting ligands altered T cell responsiveness in vitro. DBM-selected T cells lost their ability to respond to the positively selecting ligand DBM, whereas RPP-selected T cells only retained their ability to respond to high concentrations of RPP. These results demonstrate that self-peptides that mediate positive selection can differentially "tune" the activation threshold of T cells and alter the functional repertoire of T cells.

TCR Binding Kinetics Measured with MHC Class I Tetramers Reveal a Positive Selecting Peptide with Relatively High Affinity for TCR

“…We determine their binding avidities and half-lives as multimers. We show a good correlation between these results and previously reported characteristics of each peptide as an agonist, weak agonist, or antagonist and either positive or negative selector (27)(28)(29)(30)(31)(32)(33). In most cases, the negative selecting peptides have a longer half-life and higher avidity than the positive selectors.…”

“…A surprising result was the long half-life, 85.8 min, of mDBM, a natural P14-binding peptide (from dopamine ␤-monooxygenase, an enzyme expressed in the adrenal medulla), which has been shown to be a partial agonist/antagonist of P14 T cells (29,32) and a positive selector for P14-transgenic thymocytes in FTOC (33). The half-life of mDBM was more similar to the agonists than to the weak agonist/antagonist group.…”

“…In most cases, the negative selecting peptides have a longer half-life and higher avidity than the positive selectors. Most interesting is the apparently anomalous binding of a positive selecting/weak agonist peptide (29,32,33), which has a strong interaction with TCR, but a weak one with D b , resulting in its biological phenotype.…”

A Structural Basis for CD8+ T Cell-dependent Recognition of Non-homologous Peptide Ligands

“…The molecular mimicry hypothesis postulates that T cells specific for microbial mimicking epitopes can cross-react with MHCrestricted self-peptides. After an initial triggering and expansion of T cells by viral or bacterial peptide⅐MHC complexes, the T cells can cross-react with self-epitopes in the periphery, potentially triggering autoimmune responses (2,11,(13)(14)(15)(17)(18)(19)(20)(21)(22). The development of autoimmunity has been commonly associated with CD4 ϩ T cells (13).…”

“…Importantly, infection with the LCMV variant 8.7 (which contains a single pV3L mutation in the gp33 epitope) as well as with control vaccinia VSV virus did not result in any infiltration of the adrenal medulla or in alterations of dopamine levels. Furthermore, the DBM peptide, sharing limited amino acid identity with gp33, could positively select the virus-specific p14 TCR in fetal thymic culture but was unable to induce clonal deletion (20). The self-epitope was expressed in complex with H-2D b on thymic epithelial cell lines and thymocytes that were selected by H-2D b ⅐DBM proliferated vigorously in response to H-2D b ⅐gp33 complexes.…”