Bovine respiratory syncytial virus (BRSV) is an enveloped RNA virus that utilizes clathrin-mediated endocytosis for cell entry and is a significant pathogen in bovine respiratory disease (BRD). Heat shock protein family A member 4 (HSPA4), a member of the HSP70 family, is known to be involved in the progression of various cancers. However, its role in virus entry has not been previously explored. Through experiments involving Western blot analysis, virus titer, and virus copies analysis, we demonstrated that HSPA4 can regulate BRSV entry and replication. The specific regulation mode is to enhance BRSV entry by promoting clathrin-mediated endocytosis. We used Western blot, virus titer, virus copies analysis, and IFA to demonstrate that HSPA4 can promote clathrin heavy chain protein (CHC) expression and further promote BRSV entry by activating the PI3K–Akt signaling pathway. Furthermore, we observed that HSPA4 boosts the efficiency of clathrin-mediated endocytosis by increasing the ATPase activity of heat shock cognate protein 70 (HSC70), thereby facilitating BRSV entry. Additionally, our investigation into the impact of HSPA4 on the entry of other viruses revealed that HSPA4 can facilitate the entry of a variety of viruses into host cells.

Background: Rabbit hemorrhagic disease (RHD) is an acute, hemorrhagic and highly lethal infectious disease caused by rabbit hemorrhagic disease virus (RHDV), which causes huge economic losses to the rabbit breeding industry. Moreover, there is limited cross-protection between the two different serotypes of classic RHDV (GI.1) and RHDV2 (GI.2). The shortcomings of traditional inactivated vaccines have led to the development of novel subunit vaccines that can protect against both strains, and the VP60 capsid protein is the ideal antigenic protein. This study focused on developing a bivalent RHDV vaccine that can prevent infection with both GI.1 and GI.2 strains. Methodology: Baculovirus vectors containing classic RHDV and RHDV2 VP60 were co-transfected with linearized baculovirus into sf9 cells and transferred to baculovirus via homologous recombination of the VP60 gene. Infected sf9 cells were lysed, and after purification via Ni-NTA chromatography, VLPs were observed using transmission electron microscopy (TEM). In order to evaluate the immunogenicity of the chimeric RHDV VLP vaccine in rabbits, the RHDV VP60-specific antibody, IL-4, IFN-γ and neutralizing antibody titers were analyzed in serum using ELISA and HI. Results: The recombinant baculovirus system successfully expressed chimeric RHDV VLPs with a diameter of 32–40 nm. After immunization, it could produce specific antibodies, IL-4 and IFN-γ. Following the second immunization, neutralizing antibodies, determined using hemagglutination inhibition (HI) assays, were elicited. Conclusions: These data show that the chimeric RHDV VLP bivalent vaccine for immunized New Zealand rabbits can induce humoral immunity and cellular immunity in vivo, and the immunization effect of the high-dose group is similar to that of the current commercial vaccine.