To gain a comprehensive understanding of regulation of immune response and resistance to NDV in chickens, however, we must also investigate gene expression response to NDV in other immune organs. Previously, we have compared the transcriptomic response to NDV in trachea between NDV-challenged and non-challenged chickens, as well as between the two chicken lines at 2, 6 and 10 dpi 13. Therefore, we hypothesize that Fayoumis are relatively resistant to NDV compared to Leghorns. When the two chicken lines were infected with the same amount of a B1 type La Sota Lentogenic NDV strain, Fayoumis showed faster viral clearing than Leghorns from 2 to 6 days post infection (dpi) and produced more antibody in serum at 10 dpi compared to Leghorns 13. Its robust resistance to some avian diseases, such as Salmonella 8, Eimeria 9, 10, Marek’s disease 11 and avian influenza 12 has been reported. The Fayoumi line was derived from Egyptian fowl imported to the U.S. Two genetically distant inbred chicken lines – Fayoumi and Leghorn – provide a discovery platform to investigate genetic regulation of response and resistance to NDV. The ability of the host to expel pathogens and to limit their proliferation and shedding are components of resistance 7. However, few studies have reported gene expression responses to NDV in different chicken lines. There have been studies investigating host genetic regulation in response to different NDV strains 5, 6. The severity of infection with the same NDV strain also varies between avian species and chicken breeds due to genetic variation 3. NDV strains can be classified from least to most virulent into lentogenic, mesogenic, and velogenic strains 4. The outcome of NDV infection depends on both the virulence of the NDV strain and the ability of chickens to resist to the virus. To ameliorate the negative impact of NDV, alleviate poverty and improve food security in these countries, genetic selection and breeding approaches can be utilized, in addition to NDV vaccination, to enhance resistance of chickens to NDV. In addition, advanced vaccines and reliable infrastructure for transportation and storage of the vaccine are usually scarce in developing countries 3, leading to mortality of chickens as high as 80% caused by the velogenic NDV that is endemic in these areas. Although vaccination has greatly reduced outbreaks of the endemic disease, it cannot prevent the continuous evolution of ND virus (NDV) 1 and some virulent strains can still survive in vaccinated chickens 2. Newcastle disease (ND) is a highly infectious disease that causes substantial economic losses to the global poultry industry. The identified DEGs and predicted pathways may contribute to differential responses to NDV between the two chicken lines and provide potential targets for breeding chickens that are more resistant to NDV. Pathways predicted by IPA analysis, such as "EIF-signaling", "actin cytoskeleton organization nitric oxide production" and "coagulation system" may contribute to resistance to NDV in Fayoumi chickens. Several interferon-stimulated genes were identified as important DEGs regulating immune response to NDV in chicken. At a false discovery rate <0.05, Fayoumi chickens, which are relatively more resistant to NDV, showed fewer differentially expressed genes (DEGs) than Leghorn chickens. Through transcriptome analysis, gene expression in spleen at 2 and 6 days post-inoculation was compared between NDV-infected and control groups, as well as between chicken lines. In this study, two inbred chicken lines with different responses to NDV, Fayoumi and Leghorn, were challenged with LaSota NDV strain at 21 days of age. Enhancing genetic resistance of chickens to Newcastle Disease Virus (NDV) provides a promising way to improve poultry health, and to alleviate poverty and food insecurity in developing countries.
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