Abstract
Infectious bursal disease virus (IBDV) is a highly contagious pathogen that causes damage in lymphoid organs and remains a threat to the poultry industry worldwide. Currently, subunit vaccines based on VP2 antigen expressed in prokaryotic systems are widely used in clinical settings. However, the immunogenicity of VP2 vaccines is limited because of their inherent defect that the structure of the antigen expressed in Escherichia coli (E. coli) may be different from its natural conformation. In this study, we fused VP2 and VP5 protective antigen genes and linked the chicken IgY Fc gene onto it. The eukaryotic expression plasmid carrying the fusion gene was transformed into Pichia pastoris (P. pastoris) to express the recombinant VP2–VP5–Fc protein. The recombinant protein was used as immunogen for evaluating immune response, and the recombinant VP2–Fc and VP2 proteins expressed in P. pastoris and the commercial VP2 subunit vaccines were used as controls. Moreover, Taishan Pinus massoniana pollen polysaccharide (TPPPS), an immunomodulator found by our laboratory, was used as adjuvant to investigate its immune modulatory effects on immunogens. Chickens were divided into six groups and inoculated with VP2–VP5–Fc+TPPPS, VP2–VP5–Fc, VP2–Fc, VP2 vaccine, commercial VP2 subunit vaccine, and phosphate buffered saline (PBS). The recombinant VP2 subunit vaccine expressed in P. pastoris exhibited higher immunogenicity than the commercial VP2 subunit vaccine. The VP2–Fc protein showed a better effect than the VP2 protein, and the VP2–VP5–Fc subunit further improved the immune effects. In addition, TPPPS was proved to be a good immunopotentiator for the VP2–VP5–Fc subunit vaccine. Hence, the recombinant VP2–VP5–Fc subunit combined with TPPPS adjuvant exhibits potential as efficient IBDV vaccine to prevent infectious bursal disease.
Highlights
Infectious bursal disease (IBD) is a highly contagious and immunosuppressive disease in young chickens and still poses a potential threat to the poultry industry
The VP2 and VP5 genes of Infectious bursal disease virus (IBDV) and chicken IgY Fc gene were separately amplified by Polymerase chain reaction (PCR), and these genes were linked via overlapping PCR
Western blot analysis was performed with mouse anti-IBDV polyclonal antibody, anti-His tag antibody, and rabbit anti-chicken IgY antibody to determine the expression of the target proteins; we observed single reaction bands corresponding to the bands in SDS-PAGE, which indicates the expression of the recombinant VP2, VP2–Fc, and VP2–VP5–Fc proteins and their good reactogenicity to specific antibody (Figure 1B)
Summary
Infectious bursal disease (IBD) is a highly contagious and immunosuppressive disease in young chickens and still poses a potential threat to the poultry industry now. IBD is caused by the IBD virus (IBDV), a non-enveloped RNA virus in the family of Birnaviridae (Mundt et al, 1995), which mainly destroys the B lymphocyte precursors in bursa that leads to the lymphoid depletion of B cells and marked atrophy of the bursa, thereby leading to the severe immunosuppressive disease (Sharma et al, 2000; Yao and Vakharia, 2001; Liu and Vakharia, 2004). The lack of appropriate post-translational processing mechanisms in E. coli leads to the great difference between the expressed viral epitopes and its natural structure (Gonzalez-Montalban et al, 2007; Martinez-Alonso et al, 2008). The immunogenicity of the VP2 subunit vaccine is limited. How to enhance the immunogenicity of IBDV subunit vaccine is crucial for preventing this disease
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