Evaluation Of Immune Efficacy On Multi-epitope DNA Vaccines Against Infectious Bronchitis Virus In Chicken

Avian infectious bronchitis(Infectious bronchitis,IB)is one of the most important viral diseases in poultry industry.Because of numerous serotypes and weak immune cross protection of avian infectious bronchitis virus(Infectious bronchitis virus,IBV),it’s great difficult to prevent and control infectious bronchitis.Attenuated vaccine is used in the poultry industry extensively,but it may cause reversion of virulence.The immune effects of inactivated vaccine on coronavirus infection is short and its side effects may be more severe and longer local reactions.Therefore,the development of DNA vaccines and other new types of genetically engineered vaccine is useful to improve the IBV immune protection.IBV spike(S)protein causes gene mutation,and the S protein also can induce protective immunity.Therefore,T cell antigen epitope box of IBV structural protein gene S1,B cell epitopes and T cell epitopes of S1 gene in Australia T strain and M41 strain,T cell and B cell multi-epitope box were screened to connect into the eukaryotic expression vector to construct eukaryotic expression plasmid.After boosting SPF chicken,indirect ELISA method was used to detect serum antibody levels,and the protection ratio evaluated the immune effect of the DNA vaccine after challenge.IBV structure protein gene S1,T cell antigen epitope box of IBV structural protein gene S1 and IBV structure protein gene M were applicating to construct 3 group eukaryotic expression plasmid pVAX-S1,pVAX-S1T+M and pVAX-S1+S1T+M.T cell antigen epitope box of IBV structural protein gene S1 and B cell antigen epitope box of S1 gene in Australia T strain and M41 strain,building into 4 group nuclear expression plasmid,pVAX-S1B(M41),pVAX-S1B(T),pVAX-S1T+S1B(M41)and pVAX-S1T+S1B(T).Optimized multi-epitope eukaryotic expression plasmid,pVAX-S1B+S1T.Each group extracting plasmid solution was administered to the 7 days old SPF chickens by intramuscularly injection.After two weeks,the chickens were boosted by equivalent dosage of DNA vaccine.Anti-IBV specific antibodies were measured after the booster,respectively.After 30 days,chickens were challenged by virulent IBV strains.IgG antibody titer results showed that Group pVAX-S1 and pVAX-S1T+M were different from Group PBS(p<0.05)significantly.Group pVAX-S1B(T),pVAX-S1T+S1B(M41)and pVAX-S1T+S1B(T)were significant different with Group PBS(p<0.05).Group pVAX-S1B(T)and pVAX-S1B+S1T,comparing with Group PBS,has significant difference(p<0.05).Challenge test results showed that Group pVAX-S1 and pVAX-S1T+M induced immune responses of the chicken,the protection rate can provided to 80%(8/10)and 70%(7/10),respectively.Group pVAX-S1 and pVAX-S1B(T)protection efficiency was 75%(6/8).After immunization,Group pVAX-S1B(T)and pVAX-S1B+S1T protection rate was 84.7%(11/13)and 69.3%(9/13),respectively.To sum up,this result showed that the new screening IBV epitope antigen caused protecting effect effectively.It maybe a new approach to develop safe and effective IBV vaccine.