Protective immune response of recombinant Fiber-2 protein as subunit vaccine against Fowl-adenovirus-4 infection in Pakistan

Abstract

Background: Hydropericardium Syndrome (HPS) has emerged as a major viral disease of poultry industry causing huge economic losses in the recent past years. Its etiological agent, Fowl adenovirus-4 (FAdV-4) has been reported in the various countries including Pakistan. Various strategies including inactivated vaccines, are being devised to control the disease since its appearance. Subunit vaccines based on viral structural proteins have demonstrated more promising protection against FAdV-4 infection than commercial inactivated vaccines. Among different viral structural proteins, Fiber protein (mainly Fiber-2) has been as a suitable candidate for developing the recombinant subunit vaccine against HPS.Methods: Considering the importance of the Fiber-2 gene, the pET28a expression vector was utilized to clone its open reading frame, which was subsequently expressed as an oligo-histidine tagged fusion protein in BL21 cells of Escherichia coli via the IPTG induction method. The expressed recombinant fiber-2 protein was purified using nickel (Ni2+) affinity chromatography and used as a subunit vaccine in broiler birds following challenge with pathogenic FAdV-4 isolate. The immunological response was evaluated using ELISA.Results: The gene for the Fiber-2 protein was effectively cloned and expressed as a soluble 60 kDa protein, as detected by SDS-PAGE and western blot analysis. The protective efficacy of subunit vaccine was assessed by ELISA which showed the highest protection (80%) against the virus challenge than that of commercial inactivated vaccine (70%).Conclusion: The recombinant fiber-2 protein was determined to be a good option for a recombinant subunit vaccination to control HPS.Keywords: Poultry; Fowl-adenovirus-4; Subunit vaccine