Construction And Immunoefficiency Of Gene Engineer Vaccines Against Edwardsiella Tarda

As a fish pathogen, Edwardsiella tarda is the etiological agent of a severe systematic disease called edwardsiellosis, which affects many economically important fish species cultured worldwide.Three E. tarda antigens, Eta21,Eta6 and FliC, which are homologues to a putative peptidase, an ecotin precursor and the FliC flagellin respectively, were identified by in vivo-induced antigen technology from a pathogenic E. tarda strain TX01 isolated from diseased fish. When used as a subunit vaccine, purified recombinant Eta21 was effective against lethal E. tarda challenge in a Japanese flounder model, purified recombinant Eta6 showed moderately protectivity, whereas purified recombinant FliC elicited no apparent immunoprotectivity.DNA vaccines based on eta6 and fliC in the form of plasmids pEta6 and pFliC were constructed. Fish vaccinated with pEta6 and pFliC exhibited RPS of 50% and 33%, respectively.Meanwhile, a chimeric DNA vaccine, pCE6, which encodes Eta6 fused in-frame to FliC, was found to induce significantly higher level of protection than pEta6. Likewise, another chimeric DNA vaccine, pCE18, which expresses FliC fused to a previously identified E.tarda antigen Et18, elicited significantly stronger protective immunity than theDNA vaccine based on et18 alone. Fish immunized with pEta6 and pCE6 produced specific serum antibodies and exhibited significantly enhanced expression of the genes encoding elements that are involved in both innate and adaptive immune responses. Furthermore, the induction magnitudes of most of these genes were significantly higher in pCE6-vaccinated fish than in pEta6-vaccinated fish. In order to improve the immunoprotective efficacy of Eta21, the chimera pTAET21 was constructed, which consists of Eta21 fused in-frame to the secretion domain of agaV, an extracellularβ-agarase. Vaccination of Japanese flounder with live DH5a/pTAET21,which harboring plasmid pTAET21, elicited immunoprotection that is significantly higher in level than that induced by vaccination with purified recombinant Eta21.