Aim: To investigate cellular immune responses against CD8(+) T cell epitopes delivered by attenuated Salmonella.
Methods: Prokaryotic expression plasmid ptG2F, carrying the oligonucleotide fragment encoding CD8(+) T cell epitope of OVA 257-264aa and LCMV NP 118-132aa fused with GFP gene was constructed and electro-transformed into the attenuated strain SL7207 of Salmonella typhimurium. The recombinant bacteria, named as SL7207(ptG2F), were screened out. C57BL/6 and BALB/c mice were immunized intravenously with SL7207(ptG2F) at two weeks intervals. Murine IFN-gamma and IL-4 secreting cells were detected in murine splenocytes after second and third immunization by Enzyme-linked immunospot assay (ELISPOT).
Results: The recombinant bacteria SL7207(ptG2F) induced cellular immune responses. When OVA CD8(+) T cell epitope was presented by the recombinant bacteria, the immune responses were biased toward Th1 response after second immunization and then switched to the Th1 and Th2 balance after third immunization. In contrast, when the LCMV NP CD8(+) T cell epitope was presented, the level of Th2 immune response was higher than that of Th1 after both second and third immunization.
Conclusion: Attenuated Salmonella can effectively deliver the CD8(+) T cell epitopes and induce specific cellular immune responses. The results provide useful information for developing attenuated bacteria as novel vectors.