FIG. 5.
Previous immunization with attenuated L. monocytogenes decreases the response against newly introduced bacterial antigens. Naïve BALB/c mice were challenged with recombinant L. monocytogenes NPs or L. monocytogenes NPns. Previously immunized mice had received 106 CFU of actA-deficient L. monocytogenes 28 days earlier and were then challenged with 3 × 105 CFU of L. monocytogenes NPs or L. monocytogenes NPns. The number of antigen-specific CD8+ T cells per spleen was determined by intracellular cytokine staining for IFN-γ. Data are from a representative experiment of six independent experiments and are means ± SDs for three mice/group.