Strain specificity of bovine Theileria parva-specific cytotoxic T cells is determined by the phenotype of the restricting class I MHC.

To determine whether the major histocompatibility complex (MHC) phenotype of cattle could affect the parasite strain specificity of immunity to Theileria parva by influencing the antigenic specificity of Theileria-specific cytotoxic T lymphocytes (CTL), we investigated the parasite strain specificity of Theileria-specific CTL clones derived from cattle of different class I MHC phenotypes. Thirty-one class I-restricted CTL clones were generated from four cattle immunized with the Muguga stock of T. parva. The MHC restriction and parasite strain specificities were determined for each clone utilizing as targets, parasitized cell lines of different MHC phenotypes and cloned cell lines containing different parasite strains. CTL clones restricted by the same MHC determinant had similar parasite strain specificities. On the other hand, clones restricted by different MHC determinants exhibited different parasite strain specificities. This was true whether the clones were generated from the same animal or from different cattle and tested on a target cell line expressing both MHC determinants. These results provide strong evidence that differences in the strain specificities of CTL derived from animals immunized with the same parasite stock, are determined by the class I MHC phenotype of the immunized animal.