Spleens were aseptically removed from mice at day 9 postinfection with the wild type Lm, the wild type L.inn, or the L.inn::vgc strain. Spleen cells were isolated and antigen (LLO 91-99 ) specific IFN-c producing CD8+T cells were determined in the spleens of mice after i.v. infection with the same bacterial strains mentioned above by using an ELISPOT system as previously described [23, 35] .