Entry of Listeria into the cytosol is a critical event for CD8 + T cell recognition and induction of immunity [22] . In order to establish the correlation between the protection of mice preinfected with Lm or the L.inn::vgc strain upon lethal challenge and the induction of CD8 + T cells in response to infection, the generation of antigen-specific MHC class I restricted CD8 + T cells were quantitatively examined. The numbers of antigen-specific MHC class I restricted effector CD8 + T cells induced in mice spleens 9 days after primary infection and 5 days after challenge with the wild type Lm (2610 3 ) was determined through evaluation of the number of IFN-c producing CD8+ T cells induced showing reactivity against the dominant H-2K d restricted LLO 91-99 epitope [25] in an in vitro ELISPOT assay. As shown in Fig. 4B , infection with wild type Lm as well as the L.inn::vgc strain induced significant numbers of LLO 91-99 specific CD8 + T-cells. After recall infection the numbers of LLO 91-99 specific CD8 + T-cells showed a significant increase. On the other hand, infection with L.inn failed to induce a significant number of CD8 + T-cells either after primary infection or after challenge.