CD8 T cell responses against the immunodominant Theileria parva 1 peptide Tp249-59 are composed of two distinct populations specific for 2 overlapping 11-mer and 10-mer epitopes 3 Short title: Overlapping 11- and 10-mer CD8+ T cell epitopes in Tp2. 4

摘要

Immunity against Theileria parva is associated with CD8 T-cell responses\udthat exhibit immunodominance, focusing the response against limited\udnumbers of epitopes. As candidates for inclusion in vaccines, characterization\udof responses against immunodominant epitopes is a key component\udin novel vaccine development. We have previously demonstrated that the\udTp249–59 and Tp1214–224 epitopes dominate CD8 T-cell responses in BoLAA10\udand BoLA-18 MHC I homozygous animals, respectively. In this\udstudy, peptide–MHC I tetramers for these epitopes, and a subdominant\udBoLA-A10-restricted epitope (Tp298–106), were generated to facilitate accurate\udand rapid enumeration of epitope-specific CD8 T cells. During validation\udof these tetramers a substantial proportion of Tp249–59-reactive T\udcells failed to bind the tetramer, suggesting that this population was\udheterogeneous with respect to the recognized epitope. We demonstrate\udthat Tp250–59 represents a distinct epitope and that tetramers produced\udwith Tp50–59 and Tp49–59 show no cross-reactivity. The Tp249–59 and\udTp250–59 epitopes use different serine residues as the N-terminal anchor\udfor binding to the presenting MHC I molecule. Molecular dynamic modelling\udpredicts that the two peptide–MHC I complexes adopt structurally\uddifferent conformations and Tcell receptor b sequence analysis showed\udthat Tp249–59 and Tp250–59 are recognized by non-overlapping T-cell\udreceptor repertoires. Together these data demonstrate that although differing\udby only a single residue, Tp249–59 and Tp250–59 epitopes form distinct\udligands for T-cell receptor recognition. Tetramer analysis of T. parva-specific\udCD8 T-cell lines confirmed the immunodominance of Tp1214–224 in\udBoLA-A18 animals and showed in BoLA-A10 animals that the Tp249–59\udepitope response was generally more dominant than the Tp250–59 response\udand confirmed that the Tp298–106 response was subdominant.