The effects of IL-1β, IL-8, G-CSF and TNF-α as molecular adjuvant on the immune response to an E. tarda subunit vaccine in flounder (Paralichthys olivaceus)

Cytokines play vital roles in mounting immune responses and activating host defense network. In this study, the expression plasmid pcDNA3.1 (pcN3) encoding four flounder (Paralichthys olivaceus) cytokines including IL-1 beta, TNF-alpha, IL-8 or G-CSF (pcIL-1 beta, pcTNF-alpha, pcIL-8 and pcG-CSF) were successfully constructed, and their adjuvant potential on an Edwardsiella tarda (E. tarda) subunit vaccine OmpV (rOmpV) were comparatively analyzed in vaccinated flounder model. Results revealed that flounder vaccinated with rOmpV plus pcIL-1 beta, pcIL-8 or pcGCSF produced the relative percent survivals (RPS) of 71%, 65% and 49% respectively, which were higher than that in flounder vaccinated with rOmpV plus pcTNF-alpha (39%) or pcN3 (36%, the control group). Immunological analysis showed that: (1) except pcTNF-alpha, higher levels of anti-E. tarda serum antibodies and sIg + lymphocytes in spleen, head kidney and peripheral blood were significantly enhanced by pcIL-1 beta, pcIL-8 or pcG-CSF, however, pcIL-8 and pcIL-1 beta enhanced higher levels of slg + lymphocytes and anti-E. tarda antibodies than pcG-CSF; (2) pcTNF-alpha could promote the up-regulation of genes participated in cellular immunity (MHCI alpha, IFN-gamma, CD8 alpha and CD8 beta), pcIL-1 beta could enhance the expression of genes related to humoral immunity (CD4-1, CD4-2, MHCII alpha and IgM), and all the detected genes were augmented by pcIL-8 and pcG-CSF; Among the four cytokines, pcIL-8 and pcIL-1 beta could strengthen the highest levels of genes participated in cellular immunity and humoral immunity, respectively. These results demonstrated that pcIL-8 and pcIL-1 beta could enhance stronger cellular and/or humoral immunity induced by rOmpV than pcG-CSF and pcTNF-alpha, and evoked higher RPS against E. tarda challenge in flounder, which indicated that pcIL-8 and pcIL-1 beta are promising adjuvants of vaccines in controlling E. tarda infection.