Recombinant Lactococcus lactis Expressing Grass Carp Reovirus VP6 Induces Mucosal Immunity Against Grass Carp Reovirus Infection

Abstract

Grass carp haemorrhagic disease caused by grass carp reovirus II is a serious disease of the aquaculture industry and vaccination is the only effective method of GCRV protection. In this study, Lactococcus lactis was used as oral vaccine delivery to express the GCRV II VP6 protein. We evaluated the protective efficacy of the live vaccine strain to induce mucosal immune protection. After oral administration, the recombinant strains remained in the hindgut for antigen presentation and increased the survival rate 46.7% and the relative percent survival 42.9%, respectively versus control vaccination. Though L. lactis alone can induce the inflammatory response by stimulating the mucosal immune system, the recombinant L. lactis expressing VP6 greatly enhanced nonspecific immune responses via expression of immune related genes of the fish. Furthermore, both systemic and mucosal immunity was elicited following oral immunization with the recombinant strain and this strain also elicited an inflammatory response and cellular immunity to enhance the protective effect. L. lactis can therefore be utilized as a mucosal immune vector to trigger high levels of immune protection in fish at both the systemic and mucosal levels. L. lactis is a promising candidate for oral vaccine delivery.

Structure, function and immune evasion strategies of aquareoviruses, with focus on grass carp reovirus

“…Compared with inactivated vaccine and live‐attenuated vaccine, the recombinant subunit vaccine and DNA vaccine could effectively present antigen epitope and safely stimulate cellular and humoral immune response 176 . For recombinant subunit vaccines, the protective antigen epitopes of GCRV proteins are expressed in different expression systems such as E. coli , Bacillus subtilis , Lactococcus lactis , Saccharomyces cerevisiae and Baculovirus in vitro using recombinant DNA technology 177–181 . Research has reported that the recombinant fibre protein VP56, outer capsid proteins such as VP35 and VP7, and the inner capsid proteins such as VP3, VP4 and VP6 can effectively elicit a protective immune response against GCRV infection 49,180,182–184 .…”

“…176 For recombinant subunit vaccines, the protective antigen epitopes of GCRV proteins are expressed in different expression systems such as E. coli, Bacillus subtilis, Lactococcus lactis, Saccharomyces cerevisiae and Baculovirus in vitro using recombinant DNA technology. [177][178][179][180][181] Research has reported that the recombinant fibre protein VP56, outer capsid proteins such as VP35 and VP7, and the inner capsid proteins such as VP3, VP4 and VP6 can effectively elicit a protective immune response against GCRV infection. 49,180,[182][183][184] Interestingly, the VP4 gene of GCRV-II is divided into 4 segments and used for screening for potential antigen epitope.…”