Immunodominant and subdominant CTL responses to Listeria monocytogenes infection.

Protective immunity to infection by intracellular pathogens begins with expansion of Ag-specific, effector T lymphocytes and is followed by persistence of pathogen-specific memory T cells. Infection by Listeria monocytogenes, an intracellular bacterium, induces cytolytic T lymphocytes that mediate systemic sterilization and long term immunity. In cells infected with L. monocytogenes, H2-Kd class I molecules present three nonamer peptides, listeriolysin (LLO) 91-99, p60 217-225, and p60 449-457, to CTL. Herein we show that during the peak CTL response to L. monocytogenes infection, the ratio of T cells specific for LLO 91-99, p60 217-225, and p60 449-457 is approximately 20:10:1, respectively. While the number of Ag-specific T lymphocytes decreases in the weeks after infection, the proportion of T lymphocytes specific for the three epitopes is maintained. Repertoire analysis of a subset of L. monocytogenes-specific T cells, using alanine-substituted variants of p60 217-225, indicates that the range of T cell specificities is maintained by memory cells. These results indicate that the breadth and relative magnitude of T cell specificities initially elicited by an infection are transmitted to the memory compartment. Our results suggest that T lymphocytes with different gross and fine Ag specificities are equally likely to become memory T cells.