Fig. 5.

Effector memory but not CCL3-secreting CD8⁺ T cells are present during secondary infection in mice given a primary immunization with NBS-SecA2 L. monocytogenes. BALB/c mice (10 to 12 mice per group) were immunized with PBS or 0.1× the LD₅₀ of the indicated bacteria and challenged 30 days later with 10× the LD₅₀ of wt bacteria. At 6 h after secondary challenge, spleen cells from individual mice were stained for expression of the cell surface markers CD8, CD3, CD62L, and H2-K^d/LLO_91-99 tetramers and/or restimulated in vitro with LLO_91-99 peptide for intracellular CCL3 staining and further processed for FACS analysis. Dot plots are representative of the staining obtained for CD8⁺ T cells expressing H2-K^d/LLO_91-99 tetramers. The right upper panel shows the mean frequency (± standard error of the mean [SEM]) of H2-K^d/LLO_91-99 tetramer-positive cells among the total CD8⁺ T cells. The left lower panel shows the mean frequency of H2-K^d/LLO_91-99 tetramer-specific CD62L^low (effector memory) CD8⁺ T cells among the total tetramer⁺ CD8⁺ T cells. The right lower panel represents the mean frequency (± SEM) of CCL3-secreting cells among the total CD3⁺ CD8⁺ T cells. Data are pooled results from three independent experiments with n = 15 mice. P values were calculated between groups of mice immunized with wt versus Del-SecA2 and NBS-SecA2 L. monocytogenes or injected with PBS. NS, not significant.