T Lymphocyte Responses to Listeria Infection

T lymphocytes orchestrate the immune response to intracellular pathogens. Following infection or immunization, antigen specific T lymphocytes become activated and then divide. Infection with complex pathogens elicits a T lymphocyte response with specificity for many different proteins. The magnitude of the T cell response to individual antigens can be great or small, and it does not correlate with the quantity of antigen that is presented. What determines the magnitude of the T cell response to different antigens? This question remains unanswered and is the focus of this grant application. CD8+T lymphocytes of Listeria monocytogenes infected BALB/C mice respond to 6 defined T cell epitopes. The size of the T cell response to each epitope is highly reproducible from mouse to mouse but varies between epitopes. Our first aim is to precisely quantify the expansion of T cells with different specificities in L. monocytogenes infected mice using ELISPOT ASSAYS. Mutant strains OF L. monocytogenes in which CTL epitopes have been modified or knocked-out will be used to dissect T cell responses to individual epitopes. Antigen specific T cells will be isolated from infected mice using tetrameric MHC class I/epitope complexes and analyzed in vitro for T cell receptor diversity, cytokine expression and cytolysis. The second aim of this grant is to generate two strains of T cell receptor (TCR) transgenic mice. One strain will express a TCR specific for p60 217-225 an immunodominant L. monocytogenes derived epitope. The other strain will express a TCR specific for p60 449-457, a subdominant epitope. We will use these TCR transgenic mice to obtain naive, antigen specific T cells. Naive T cells will be studied in vitro to identify possible differences in the activation of dominant and subdominant T cell responses. Naive T cells will also be transferred into recipient mice and their activation and expansion will be studied. These studies will allow us to compare the responses of T cells with specificities for dominant and subdominant epitopes. These experiments will shed light on how the size of the T cell response to an epitope is determined in vivo and are likely to provide ideas for optimizing vaccines which elicit dominant, long term T lymphocyte responses.