Construction and evaluation of an Edwardsiella tarda DNA vaccine encoding outer membrane protein C

Outer membrane protein C is a porin that resides in the outer membrane, and it has been identified as an antigenic protein in many bacteria, such as Escherichia coli, Salmonella typhi, Aeromonas hydrophila and Edwardsiella tarda. In the present work, we aimed at evaluating the immune protective potential of E. tarda OmpC as a DNA vaccine. For this purpose, a recombinant DNA plasmid encoding OmpC (pCG-OmpC) gene was constructed and its vaccine potential was analyzed in a flounder (Paralichthys olivaceus) model. The results showed that pCG-OmpC produced a relative percent survival (RPS) of 55% following E. tarda challenge at 6 w post vaccination. Moreover, OmpC transcripts and OmpC-GFP fusion protein could be detected in flounder after immunization with pCG-OmpC, and OmpC-GFP fusion protein could also be detected in HINAE cells after transfection with pCG-OmpC. Meanwhile, the immune responses induced by pCG-OmpC were investigated, and the results showed that pCG-OmpC could significantly induce the production of specific serum antibodies and the proliferation of sIg + lymphocytes in blood, spleen and pronephros. qRT-PCR analysis showed that the expressions of TLR5M, MyD88, NF-κB, MHCIα, MHCIIα, CD4-1, CD8α, IL-1β and TNF-α genes were significantly induced after vaccinated with pCG-OmpC, while there was no significant difference in expressions of TLR2 and IL-6 between pCG-OmpC and PBS injected fish. Taking together, these results indicated that pCG-OmpC could induce strong innate, humorol and cellular immune responses of flounder, and finally evoked highly protective effects, suggesting that pCG-OmpC was a promising DNA vaccine candidate.