Vaccination with CD4⁺ T cell epitopes during ongoing infection reduces the burden of <i>Salmonella</i> disease.

<p>C57BL/6 mice were infected orally with 1×10⁷ virulent <i>Salmonella</i> Typhimurium. Groups of mice (n = 7–8) were vaccinated with a mixture of the peptides AhpC_154–168, EutC_243–257, and STM1540_262–276 (8 µg (∼5 nmol) or 40 µg (∼25 nmol) of each peptide) at day 5 post-infection (therapeutic setting) or 14 days before <i>Salmonella</i> infection (prophylactic setting). Control mice received PBS without peptides. Mice were sacrificed at day 14 post-infection and (A) the <i>Salmonella</i> CFU were determined in spleen and liver, and (B) the ALT levels were determined in the serum. (C) CD4⁺ T cells purified from the spleens of the non-vaccinated mice and the mice vaccinated at day 5 post-infection (p.i.) with 40 µg of each of the peptides (AhpC_154–168, EutC_243–257, and STM1540_262–276) were restimulated with dendritic cells that were loaded with the indicated <i>Salmonella</i> peptide epitopes. Graph shows the IFN-γ⁺ spots per 2×10⁵ CD4⁺ T cells measured by ELISPOT assays. Statistical significance between the peptide vaccinated and non-vaccinated groups is indicated (Mann Whitney test, *<i>p</i><0.05). Naive mice (n = 8) were used to determine the normal serum ALT levels. Bar graphs show mean and SEM. Experiments were performed twice with similar results.