Through their production of IFNγ, CD8 T cells are important in conferring resistance against Toxoplasma. After an infection with Toxoplasma, both CD4 and CD8 T cells infiltrate the brain. Usually transgenic parasites expressing model antigens in combination with transgenic T cells have been used as models for infection. Obvious shortcomings of this approach include difficulties in controlling expression levels and localisation of the antigen, and moreover the model transgenic T cell receptors might not recognise the model antigen with physiological affinity.
We have identified three CD8 T cell epitopes derived from three distinct Toxoplasma proteins, dense granule protein GRA4, rhoptry protein ROP7 and the unnamed protein T57. Another CD8 epitope from GRA6 has been described. Using flow cytometry to sort antigen-specific CD8 T cells from Toxoplasma-infected mice, transnuclear (TN) Toxoplasma-specific CD8 T cell receptor (TCR) mice for these four Toxoplasma epitope-MHC complexes have been generated by somatic cell nuclear transfer. We have shown that transnuclear CD8 T cells specific to T57 and Gra6 are able to lower the parasite load during the acute phase of ToxoplasmainfectionInterestingly, we have three lines of mice with unique TCR sequences that ROP7 epitope-bound MHC class I albeit with different binding affinity. This enables further studies on how the binding affinity of the TCR to MHC controls CD8 T cell phenotypes and function. We are characterising and comparing naturalToxoplasma antigen-specific CD8 T cells in the chronic phase of Toxoplasma infection in the brain depending on the interaction of different TCRs with the same epitope-major histocompatibility complex.
In the future we are discontinuing this line of research.