Different approaches to expressing Edwardsiella tarda antigen GAPDH in attenuated Vibrio anguillarum for multivalent fish vaccines

Recombinant Hsp33 and OmpC protein can serve as promising divalent vaccine with protection against Vibrio anguillarum and Edwardsiella tarda in flounder (Paralichthys olivaceus)

Vibrio anguillarum and Edwardsiella tarda are severe aquaculture pathogens shared similar epidemiological characteristics and susceptible to flounder (Paralichthys olivaceus). In our previous studies, recombinant(r) protein heat shock protein 33 (rHsp33) from V. anguillarum and outer membrane protein C (rOmpC) from E. tarda were proved to have protection against V. anguillarum and E. tarda, respectively. In this paper, the cross protection of rHsp33 against E. tarda and rOmpC against V. anguillarum, and the protection of divalent vaccine candidate (rHsp33 + rOmpC, rHC) against both V. anguillarum and E. tarda were evaluated. RHC, rHsp33, and rOmpC were vaccinated to flounder, respectively, and the percentages of surface immunoglobulin-positive (sIg+) cells in peripheral blood lymphocytes (PBLs), serum IgM, specific antibodies against V. anguillarum or E. tarda, specific antibodies against rHsp33, rOmpC or rHC, the expression of immune-related genes and relative percent survival (RPS) against V. anguillarum or E. tarda were measured. The results showed that: RHC could induced the enhancement of sIg + cells and high levels of specific antibodies against both V. anguillarm and E. tarda; Also a significant increase of specific antibodies against rHsp33, rOmpC or rHC, and up-regulation of gene expression of CD3, CD4-1, CD4-2, CD8α, CD8β and IgM in spleen, head-kidney, and hindgut, RPS of 70 ± 3.45% against V. anguillarum and 60 ± 1.48% against E. tarda, respectively. In addition, rHsp33 induced specific antibodies against E. tarda and rOmpC, and had a RPS of 43.3 ± 3.73% against E. tarda; rOmpC could evoke specific antibodies against V. anguillarum and rHsp33, and had a RPS of 44 ± 1.27% against V. anguillarm; The results demonstrated that there was cross protection of rHsp33 against E. tarda and rOmpC against V. anguillarum, rHC as a divalent vaccine can induce significant immune response and efficient protection against both E. tarda and V. anguillarum in flounder.

Notable mucosal immune responses induced in the intestine of zebrafish (Danio rerio) bath-vaccinated with a live attenuated Vibrio anguillarum vaccine

Live attenuated vaccine is one of the efficient vaccine candidates in aquaculture, which can be easily delivered to fish via bath-vaccination. An outstanding advantage of bath-vaccination is that vaccine delivery is through the same route as that utilized by many fish pathogens, generating specific mucosal immune responses. In this work, we investigated the mucosal immune responses induced by a live attenuated Vibrio anguillarum vaccine in zebrafish via bath-vaccination. Bacteria proliferated rapidly in 3 h after vaccination and maintained at a high level until 6 h in the intestine. Besides, bacteria persisted in the intestine for a longer time whereas decreased rapidly in the skin and gills. Moreover, a significant up-regulation of TLR5 triggering a MyD88-dependent signaling pathway was observed in the intestine, which implied that flagella were the crucial antigenic component of the live attenuated vaccine. And macrophages and neutrophils showed active responses participating in antigen recognition and sampling after vaccination. Furthermore, an inflammation was observed with plenty of lymphocytes in the intestine at 24 h post vaccination but eliminated within 7 days. In conclusion, the live attenuated V. anguillarum vaccine induced notable mucosal immune responses in the intestine which could be used as a mucosal vaccine vector in the future.

Immune responses evoked by infection with Vibrio anguillarum in zebrafish bath-vaccinated with a live attenuated strain

Live attenuated vaccines are a promising application to control bacterial fish diseases. A live attenuated Vibrio anguillarum vaccine candidate was established in our laboratory to protect fish against vibriosis. To elucidate the mechanism of immunoprotection, it is necessary to compare the different immune responses to infection between vaccinated and non-vaccinated fish. In this study, the expression levels of pathogen-specific antibodies and immune-related genes upon challenge at 28 days post-vaccination were compared between vaccinated and non-vaccinated zebrafish. In the results, the specific antibody levels against virulent V. anguillarum in the vaccinated group did not rise significantly following infection, which suggested that high-affinity antibodies were induced by the vaccine. In the non-vaccinated group, the specific IgM response was triggered at 3 days post-infection and showed a delayed antibody response. Meanwhile, the transcription levels of the genes encoding the pro-inflammatory cytokine IL-1β and the chemokine IL-8 were more highly up-regulated in non-vaccinated fish than in vaccinated fish. This suggests that the overwhelming inflammatory response trigged by infection in non-vaccinated zebrafish was controlled in vaccinated zebrafish. Interestingly, the expression levels of adaptive immune-related genes were increased in vaccinated fish after challenge, compared to the non-vaccinated fish. These results suggest that inoculation with the live attenuated vaccine triggered protection by curbing inflammation and strengthening the adaptive immune response.