Figure 2. SCT DNA immunization induces peptide-specific CD8⁺ T cells and lowers bacterial burden in L. monocytogenes infection.

Mice were immunized with K^d/LLO_91–99 or control K^d SCT DNA three times at 3 day intervals. (A) and (B) At 5 days after the last immunization, splenocytes were harvested. (A) Splenocytes from control (left), K^d/LLO_91–99 SCT (middle), or L. monocytogenes (right)-immunized mice were stained with anti-CD8 mAb and LLO 91–99/K^d tetramers. Numbers indicate the percentage of tetramer positive cells among CD3⁺ CD8⁺ cells. Representative figures of the flow cytometry data. (B) Splenocytes from each group were stimulated in vitro with LLO 91–99 or irrelevant peptide overnight and IFNγ secretion was measured by ELISPOT. Error bars indicate SE of the experiment. The data presented are from one representative experiment of two performed independently with each group containing 4~5 mice. (C) Immunized mice were infected intraperitoneally with 2×10⁵ of L. monocytogenes at 4 weeks post immunization. For controls, mice were infected with 10³ of L. monocytogenes or left uninfected. At 3 days after infection, spleens and livers were harvested and bacteria counts were determined by colony count. Error bars indicate SEM of the experiment. Data were expressed as log10 of colony forming units (CFU). n.s., not significant. *, p<0.05 (Mann-Whitney U test).