Expression of recombinant Newcastle disease virus F protein in Pichia pastoris and its immunogenicity using flagellin as the adjuvant.

Newcastle disease (ND), a highly contagious, acute, and potent infectious disease caused by Newcastle disease virus (NDV), has a considerable impact on the global poultry industry. Although both live attenuated and inactivated vaccines are used to prevent and control the spread of ND among chickens, the increasing number of ND outbreaks in commercial poultry flocks worldwide indicates that routine vaccinations are insufficient to control ND. Hence, efforts are being invested into developing alternative and more effective vaccination strategies. In this study, we focus on F protein, the neutralizing and protective antigen of NDV, and flagellin (FliC), a toll-like receptor 5 (TLR5) agonist that is an effective inducer of innate immune responses. We amplified F gene from velogenic NDV strain F48E8. The recombinant histidine (His)-tagged F protein was efficiently expressed in a Pichia pastoris (P. pastoris) eukaryotic system and verified by sodium dodecyl sulfate polyacrylamide gel electrophoresis and western blotting. The conditions for F protein expression in P. pastoris were optimal. The immunogenicity of F protein with FliC as the adjuvant was evaluated in a C3H/HeJ mouse model. FliC was found to enhance both F-specific and NDV-specific IgG responses and F-specific cellular immune responses following intraperitoneal co-administration with F protein. Thus, the recombinant F protein expressed by P. pastoris when used with flagellin as the adjuvant has potential as a subunit vaccine candidate.