FIG. 3.

The number of antigen-specific CD8⁺ T cells generated during an immune response correlates with the immunizing dose of actA-deficient L. monocytogenes. BALB/c mice were immunized with the indicated doses (in CFU) of actA-deficient L. monocytogenes; 7 days later the number of LLO91-99-specific CD8⁺ T cells per spleen was determined by intracellular cytokine staining for IFN-γ. Representative data are from one of three independent experiments and are means plus SDs for three mice/group. Statistical analysis performed with Student’s t test resulted in P values of <0.005. Statistical analysis was also performed to compare the CD8⁺-T-cell priming observed with each of the lower doses against priming at 10⁶ CFU. Values obtained with 500 (P < 0.005), 10³ (P < 0.005), and 10⁴ (P < 0.01) CFU were all significantly different from that obtained with 10⁶ CFU. **, P < 0.005; ***, P < 0.01.