Crude extract of bacterially expressed, infectious bursal disease virus VPX/VP2 proteins induces protective immune response to the virus in chickens

Infectious bursal disease virus (IBDV) infects young chickens and causes serious lose to the poultry industry, worldwide. Previous attempts using purified bacterially expressed IBDV VP2 failed to elicit a protective immune response to the virus. This study was designed to investigate if the initial expressed protein contained neutralizing epitopes but became nonfunctional during purification steps. The full length IBDV VP2 and its precursor VPX genes from the highly virulent IBDV (hvIBDV) SDH1 isolate were cloned and expressed in BL21 bacterial cells. Specific pathogen-free (SPF) chickens were inoculated subcutaneously with 0.3 ml crude extract with/without adjuvant at week 0, 2, and 4. At week 2 post-immunization, IBDV antibody was detected in the vaccinated chickens and increased to its highest titre at week 4. Virus challenge using the SDH1 isolate did not result in IBDV specific clinical signs when chickens were vaccinated with adjuvant-extract preparation (100% protection) while mock-inoculated chickens died 3-4 days post-inoculation. The above results, taken together, demonstrated that bacterially expressed IBDV VP2 harbors neutralizing epitopes required for induction of protective response, and suggest less detrimental purification procedures for vaccine preparation.