Both granuloma formation and delayed-type-hypersensitivity footpad responses have previously been shown to be CD4 + T cell dependent inflammatory responses following infection with Lm. Morphological changes were examined in the spleens on day 3 after i.v. infection. Although the numbers of bacteria in spleens at day 3 post-infection for both Lm and L.inn::vgc were approximately the same (Fig. 1A) , distinct differences in the morphological appearance between spleens isolated from mice infected with Lm and those isolated from mice infected with L.inn::vgc were observed (Fig. 3A ). Splenomegaly associated with extensive granuloma formation was observed in spleens of Lm infected mice, as a result of intensive leukocyte infiltration which was visualized in stained spleen sections (Fig. 3B) , whereas splenomegaly in the absence of granuloma formation was observed in spleens of L.inn::vgc infected mice. Infection with the wild type L.inn did not result in any morphological changes in spleens.