FIG. 6.

Stimulation of CD4⁺ and CD8⁺ T-cell proliferation by recombinant Salmonella vaccines. BM-DC were infected with Salmonella WT (A) or the attenuated ΔpurD ΔhtrA carrier strain MvP728 (B), each harboring plasmids with various expression cassettes for expression of sseF::OVA:M45. As a control for the release of antigen independent of T3SS translocation, the T3SS-deficient ssaV strain expressing sseF::OVA::M45 under the control of P_sseA was used. The infection of BM-DC was performed basically as described for Fig. 5. Infected BM-DC and intracellular bacteria were inactivated after 3 h of infection. Inactivated cells were added to T cells prepared from OT-I or OT-II mice as indicated, and T-cell stimulation was allowed for 24 h. For quantification, the incorporation of [³H]thymidine was determined and is expressed as counts per minute (CPM). The means and standard deviations of triplicate samples are shown for CPM of OT-1 cells (black bars) or OT-II cells (gray bars). The assays are representative of three assays with similar results. Statistical analyses were performed comparing stimulation by strains harboring expression cassettes with various promoters to strains with expression cassettes with P_sseA (indicated by plain lines) or by comparing stimulation by strains with various expression cassettes to the vector control (indicated by lines with arrows). Statistical analysis: n.s., not significant; *, P < 0.05; **, P < 0.01; ***, P < 0.001.