The magnitude of GFP-specific CD8+ T cell responses as determined by quantification of IFN-γ cytokine. Groups of mice were vaccinated three times (Days 0, 28 and 56) with live recombinant Salmonella vaccine expressing GFP (AroC+GFP) or a negative Salmonella control vaccine not expressing any antigen (AroC+pGEM). On Day 84 (28 days after the last inoculation), splenocytes from the sacrificed mice were incubated with media only (negative assay control) or stimulated with GFP CD8+ T cell peptide (HYLSTQSAL), and the amounts of IFN-γ measured by CBA assay. Each bar in the graphs represents the average picogram amount of cytokine produced per 10e6 splenocytes in 48 hrs of stimulation. One asterisk indicates values that differ significantly (p < 0.05). Two asterisks indicate values that do not differ significantly (p > 0.05).