CTLs are known to contribute to immunity toward Theileria parva, the causative agent of
East Coast fever. The Tp967-75 CTL
epitope from the Muguga strain of T. parva is polymorphic in other parasite strains. Identifying the
amino acids important for MHC class I binding, as well as TCR recognition of
epitopes, can allow the strategic selection of Ags to induce cellular immunity toward T. parva In this study, we characterized the
amino acids important for MHC class I binding and TCR recognition in the Tp967-75
epitope using
alanine scanning and a series of variant
peptide sequences to probe these interactions. In a
peptide-MHC class I binding assay, we found that the
amino acids at positions 1, 2, and 3 were critical for binding to its restricting
MHC class I molecule BoLA-1*023:01. With IFN-γ ELISPOT and
peptide-MHC class I Tet staining assays on two parasite-specific bovine CTL lines, we showed that
amino acids at positions 5-8 in the
epitope were required for TCR recognition. Only two of eight naturally occurring polymorphic Tp9
epitopes were recognized by both CTLs. Finally, using a TCR avidity assay, we found that a higher TCR avidity was associated with a stronger functional response toward one of two variants recognized by the CTL. These data add to the growing knowledge on the cross-reactivity of
epitope-specific CTLs and specificities that may be required in the selection of Ags in the design of a wide-spectrum
vaccine for
East Coast fever.