Self-assembled BPIV3 nanoparticles can induce comprehensive immune responses and protection against BPIV3 challenge by inducing dendritic cell maturation in mice

Bovine parainfluenza virus type 3 (BPIV3) is one of the most important viral respiratory pathogens of cattle. No specific therapies are available for BPIV3 infection; vaccination is one of the most effective ways to prevent BPIV3 infection. We therefore prepared the self-assembled BPIV3 nanoparticles by genetically fusing the ectodomain of BPIV3 haemagglutinin-neuraminidase (HN) (HNex) to the NH2 terminus of ferritin (HNex-RFNp) using a baculovirus expression system. It was found that HNex-RFNp-induced bone marrow-derived dendritic cell (BMDC) maturation through the upregulated expression of surface molecules (MHC II, CD80, CD86, and CD40), increased the secretion of inflammatory cytokines (IL-6, IL-12, TNF-α, and IFN-γ), and reduced antigen phagocytosis and T cell activation capacity. HNex-RFNp positively regulated IκBα and NF-κB (p65) phosphorylation and facilitated NF-κB (p65) translocation into the nuclei of mature BMDCs. Incubating RFNp-treated BMDCs with TLR4 and NF-κB (p65) inhibitors, suppressed surface molecule expression as well as pro-inflammatory cytokine production and IκBα and NF-κB (p65) activities. The BPIV3 HNex protein induced BMDC maturation to some extent but was significantly weaker than HNex-RFNp. We found that HNex-RFNp induced a higher titre of specific antibodie, haemagglutinin inhibition (HI) antibody, and virus neutralisation (VN) antibody, and a comprehensive cellular immune response. We examined protection against BPIV3 challenge in a mouse model. Pathological changes were not observed in the lungs of HNex-RFNp-vaccinated mice. Levels of BPIV3 RNA and virus titres in the lungs and trachea were significantly lower in the HNex-RFNp, than HNex, inactivated BPIV3, and PBS groups. In summary, HNex-RFNp elicited better immunogenicity than HNex or inactivated BPIV3 and could be developed as an effective vaccine to protect against BPIV3 infection.