Identification of Embryonic Chicken Proteases Activating Newcastle Disease Virus and Their Roles in the Pathogenicity of Virus Used as In Ovo Vaccine

by Selleckchem | Jun 05 2023

In ovo vaccination is an attractive immunization approach for chickens. However, most live Newcastle disease virus (NDV) vaccine strains used safely after hatching are unsafe as in ovo vaccines due to their high pathogenicity for chicken embryos. The mechanism for viral pathogenicity in chicken embryos is poorly understood. Our previous studies reported that NDV strain TS09-C was a safe in ovo vaccine, and the F protein cleavage site (FCS) containing three basic amino acids (3B-FCS) was the crucial determinant of the attenuation of TS09-C in chicken embryos. Here, five trypsin-like proteases that activated NDV in chicken embryos were identified. The F protein with 3B-FCS was sensitive to the proteases Tmprss4, Tmprss9, and F7, was present in fewer tissue cells of chicken embryos, which limited the viral tropism, and was responsible for the attenuation of NDV with 3B-FCS, while the F protein with FCS containing two basic amino acids could be cleaved not only by Tmprss4, Tmprss9, and F7 but also by Prss23 and Cfd, was present in most tissue cells, and thereby was responsible for broad tissue tropism and high pathogenicity of virus in chicken embryos. Furthermore, when mixed with the protease inhibitors aprotinin and camostat, NDV with 2B-FCS exhibited greatly weakened pathogenicity in chicken embryos. Thus, our results extend the understanding of the molecular mechanism of NDV pathogenicity in chicken embryos and provide a novel molecular target for the rational design of in ovo vaccines, ensuring uniform and effective vaccine delivery and earlier induction of immune protection by the time of hatching.

IMPORTANCE As an attractive immunization approach for chickens, in ovo vaccination can induce a considerable degree of protection by the time of hatching, provide support in closing the window in which birds are susceptible to infection, facilitate fast and uniform vaccine delivery, and reduce labor costs by the use of mechanized injectors. The commercial live Newcastle disease virus (NDV) vaccine strains are not safe for in ovo vaccination and cause the death of chicken embryos. The mechanism for viral pathogenicity in chicken embryos is poorly understood. In the present study, we identified five trypsin-like proteases that activate NDV in chicken embryos and elucidated their roles in the tissue tropism and pathogenicity of NDV used as in ovo vaccine. Finally, we revealed the molecular basis for the pathogenicity of NDV in chicken embryos and provided a novel strategy for the rational design of in ovo ND vaccines.

Comments：

The study described here investigated the mechanism of pathogenicity of Newcastle disease virus (NDV) in chicken embryos, with a focus on the role of trypsin-like proteases and the F protein cleavage site (FCS). The researchers identified five proteases that activate NDV in chicken embryos and found that the F protein with a 3B-FCS was sensitive to three of these proteases, limiting the viral tropism and contributing to the attenuation of NDV in chicken embryos. In contrast, the F protein with a 2B-FCS was cleaved by all five proteases, allowing for broad tissue tropism and high pathogenicity.

The results of this study provide insight into the molecular mechanism of NDV pathogenicity in chicken embryos and offer a potential target for the rational design of safe in ovo ND vaccines. In ovo vaccination is an attractive approach for chicken immunization due to its effectiveness, uniformity, and cost-effectiveness. However, most commercial live NDV vaccine strains are not safe for in ovo vaccination. The identification of a safe in ovo vaccine strain and the elucidation of its molecular basis for attenuation may help to overcome this limitation and facilitate the development of safer and more effective in ovo vaccines.