Abstract
The virulent Newcastle disease virus (NDV) is still a significant avian viral pathogen due to its ability to reproduce respiratory, digestive, neurologic and systemic disease in chickens; severity depending upon viral virulence, tissue tropism and host immune status. Herein, we compared the relative expression of three antiviral immune genes Toll-like receptor-3 (TLR-3), interferon beta (IFN-β) and myxovirus resistance protein 1 (Mx1) in Newcastle disease virus infected chickens versus healthy ones. Included are two groups of chickens, NDV-infected group (n = 15) and Healthy Chickens (n = 10), with a total sample of twenty-five. Relative gene expression was determined by real-time quantitative polymerase chain reaction (PCR), and analyzed with the ΔCT/ΔΔCT method, expressed as 2^-ΔΔCT. In NDV-infected group, Delta cycle threshold (ΔCT) values were significantly lower and fold-change values for all genes were markedly higher. Compared with healthy chickens (1.15 ± 0.22), the expression of IFN-β in infected chickens increased to 10.68 ± 1.36 fold (P < 0.0001). Mx1 had the highest fold increase of expression, with an average of 11.65 ± 2.00 in NDV-infected group compared to healthy chickens (1.08 ± 0.13) (P = 0.00012). With a fold change of 5.02 ± 0.79 vs 1.06 ± 0.13 in the control group (P = 0.00018), TLR-3 was also significantly up regulated. In conclusion, these results showed that NDV infection in chicken triggered the central pathway for viral RNA is sensing and IFN signaling followed by inducing interferon-stimulated gene (ISG)-mediated antiviral responses against NDV. These results also underscore the relevance of TLR-3, IFN-β and Mx1 as molecular markers of immune activation that may suffer from bias based on strain, timepoint post-infection, tissue type, host genetics and vaccination status in relevant strains.

Key words: Newcastle disease virus, Chickens, TLR-3, IFN-β, Mx1, Real-time PCR, Gene expression.