Protective immune responses of recombinant VP2 subunit antigen of infectious bursal disease virus in chickens

Abstract

Infectious bursal disease virus (IBDV) is the causative agent of Gumboro disease and poses a huge threat to poultry industry. The risks associated with conventional attenuated viral vaccines make it indispensable to probe into the development of novel and rationally designed subunit vaccines which are safer as well as effective. VP2 is the major host-protective antigen found in IBDV capsid. It encompasses different independent epitopes responsible for the induction of neutralizing antibody. Here, we report the efficacy of the immunodominant fragment of VP2 which induces both humoral and cellular immunity against infectious bursal disease. A 366bp fragment (52–417bp) of the VP2 gene from an IBDV field isolate was amplified and expressed in Escherichia coli as a 21kDa recombinant protein. The efficacy of rVP252–417 antigen was compared with two commercial IBDV whole virus vaccine strains. The rVP252–417 induced significantly high antibody titres in chicken compared to commercial vaccines and the anti-rVP252–417 sera showed reactivity with viral antigens from both commercial strains (P<0.0001) and field isolates. Also, the chicken splenocytes from rVP252–417 immunized group showed a significantly high proliferation (P<0.01) compared to other groups, which implies that the rVP252–417 fragment contains immunogenic epitopes capable of eliciting both B and T cell responses. Further, rVP252–417 conferred 100% protection against vIBDV challenge in the immunized chickens which was significantly higher (P<0.001) compared to 55–60% protection by commercial vaccine strains. Hence, the study confirms the efficacy of the immunodominant VP2 fragment that could be used as a potent vaccine against IBDV infection in chicken.