Evolution of a Complex T Cell Receptor Repertoire during Primary and Recall Bacterial Infection

The mechanisms underlying the genesis and maintenance of T cell memory remain unclear. In this study, we examined the evolution of a complex, antigen-specific T cell population during the transition from primary effector to memory T cells after Listeria monocytogenes infection. T cell populations specific for listeriolysin O (LLO)_91–99, the immunodominant epitope recognized by H2-K^d–restricted T lymphocytes, were directly identified in immune spleens using tetrameric H2-K^d–epitope complexes. The T cell receptor (TCR) Vβ repertoire of specific T cells was determined by direct, ex vivo staining with a panel of mAbs. We demonstrate that LLO_91–99-specific, primary effector T cell populations have a diverse TCR Vβ repertoire. Analyses of memory T cell populations demonstrated similar TCR diversity. Furthermore, experiments with individual mice demonstrated that primary effector and memory T cells have indistinguishable TCR repertoires. Remarkably, after reinfection with L. monocytogenes, LLO_91–99-specific T cells have a narrower TCR repertoire than do primary effector or memory T cells. Thus, our studies show that the TCR repertoire of primary effector T lymphocytes is uniformly transmitted to memory T cells, whereas expansion of memory T cells is selective.