Background: H9N2 virus is mainly transmitted through the respiratory mucosal pathway, so mucosal immunity is considered to play a good role in controlling avian influenza infection. It is commonly accepted that no adequate mucosal immunity is achieved by inactivated vaccines, which was widely used to prevent and control avian influenza virus infection. Thus, an improved vaccine to induce both mucosal immunity and systemic immunity is urgently required to control H9N2 avian influenza outbreaks in poultry farms. Methods: In this study, we constructed a novel Lactococcus lactis (L. lactis) strain expressing a recombinant fusion protein consisting of the HA1 proteins derived from an endemic H9N2 virus strain and chicken IgY Fc fragment. We evaluated the immunogenicity and protective efficacy of this recombinant L. lactis HA1-Fc strain. Results: Our data demonstrated that chickens immunized with L. lactis HA1-Fc strain showed significantly increased levels of serum antibodies, mucosal secretory IgA, T cell-mediated immune responses, and lymphocyte proliferation. Furthermore, following challenge with H9N2 avian influenza virus, chickens immunized with L. lactis HA1-Fc strain showed reduced the weight loss, relieved clinical symptoms, and decreased the viral titers and the pathological damage in the lung. Moreover, oropharyngeal and cloacal shedding of the H9N2 influenza virus was detected in chicken immunized with L. lactis HA1-Fc after infection, the results showed the titer was low and reduced quickly to reach undetectable levels at 7 days after infection. Conclusion: Our data showed that the recombinant L. lactis HA1-Fc strain could induce protective mucosal and systemic immunity, and this study provides a theoretical basis for improving immune responses to prevent and control H9N2 virus infection.

Feline panleukopenia, caused by feline parvovirus (FPV), is a highly infectious disease characterized by leucopenia and hemorrhagic gastroenteritis that severely affects the health of large wild Felidae. In this study, tiger FPV virus-like particles (VLPs) were developed using the baculovirus expression system. The VP2 gene from an infected Siberian tiger (Panthera tigris altaica) was used as the target gene. The key amino acids of this gene were the same as those of FPV, whereas the 101st amino acid was the same as that of canine parvovirus. Indirect immunofluorescence assay (IFA) results demonstrated that the VP2 protein was successfully expressed. SDS-PAGE and Western blotting (WB) results showed that the target protein band was present at approximately 65 kDa. Electron micrograph analyses indicated that the tiger FPV VLPs were successfully assembled and were morphologically similar to natural parvovirus particles. The hemagglutination (HA) titer of the tiger FPV VLPs was as high as 1:2¹⁸. The necropsy and tissue sections at the cat injection site suggested that the tiger FPV VLPs vaccine was safe. Antibody production was induced in cats after subcutaneous immunization, with a >1:2¹⁰ hemagglutination inhibition (HI) titer that persisted for at least 12 months. These results demonstrate that tiger FPV VLPs might provide a vaccine to prevent FPV-associated disease in the tiger.

Porcine epidemic diarrhea virus (PEDV) is a highly contagious coronavirus that induces diarrhea and death in neonatal piglets, resulting in substantial economic losses to the global swine industry. The mechanisms of PEDV infection and the roles of host factors are still under exploration. In this study, we used the ferroptosis pathway downstream target activator (1S,3R)-RSL3 compound as a starting point, combined with the interactions of N-acetylcysteine and deferoxamine, to elucidate the effects of a series of compounds on PEDV proliferation. We also established glutathione peroxidase 4 (GPX4) gene overexpression to further elucidate the relationship between the ferroptosis pathway and PEDV. (1S,3R)-RSL3 inhibited PEDV replication in Vero cells, while N-acetylcysteine and deferoxamine promoted its proliferation. In addition, (1S,3R)-RSL3 mainly affected the replication stage of PEDV. Overexpression of GPX4 promoted PEDV proliferation, indicating that the ferroptosis pathway could influence PEDV replication in Vero cells. This study focused on the mechanism of (1S,3R)-RSL3 inhibition on PEDV, laying the foundation for exploring the pathogenic mechanisms of PEDV and drug development.

Previous studies have shown that wild-type (wt) rabies virus (RABV) evades the host immune response by restricting expression of glycoprotein (G), which blocks activation of dendritic cells (DCs) and induces production of virus-neutralizing antibodies (VNAs). In the present study, wt RABVs not only restricted G expression but also reduced incorporation of G into mature virions compared with laboratory-adapted viruses. A recombinant RABV expressing triple G was used to further determine whether G expression relates to incorporation. The recombinant virus showed higher expression and incorporation of G and activated more DCs than the virus that expressed a single copy of G. Removal of G from viruses using subtilisin or Dithiothreitol (DTT)/ Nonidet P-40 (NP40) almost completely abolishes DC activation and VNA production. Consequently, these G-depleted viruses cause lethal infection in mice. Thus, wt RABVs can subvert DC-induced antiviral immune response and maintain pathogenicity by decreasing G expression in infected cells and G incorporation into virions.