Newcastle disease virus infection in chicken embryonic fibroblasts but not duck embryonic fibroblasts is associated with elevated host innate immune response

Background: Chickens and ducks are major hosts of Newcastle disease virus (NDV) with distinct responses to infection. However, whereas ducks are generally asymptomatic or exhibit only mild symptoms following NDV infection and are thus regarded as potential long-term reservoirs of the virus, chickens exhibit severe clinical lesions, transient infections and even death due to NDV infection. These differences may in part result from the host innate immune response to NDV infection. Methods: To better understand the host innate immune response to NDV infection in avian species, by using the quantitative real-time polymerase chain reaction method we examined the messenger RNA expression levels of immune-related genes in chicken embryonic fibroblasts (CEFs) and duck embryonic fibroblasts (DEFs) when infected with NDV of different pathogenicities. Results: Gene expression profiles showed that the expression of IL-1beta, TNF-a-like factor (LITAF) and interferon (IFN)-beta was upregulated in both CEFs and DEFs infected with SS-10 and NH-10 viruses or treated with polyinosinic: polycytidylic acid [poly(I: C)], as well as that expression levels were greater in CEFs than in DEFs. The expression of TLR3, TLR7, IL-6, IFN-alpha, IFN-gamma, MHC-I and MHC-II, except for IL-8, were also greater in CEFs than in DEFs in response to infection to both viruses or treatment with poly(I: C). However, unlike moderate virulent NH-10, highly virulent SS-10 induced greater pattern recognition receptors and cytokines, except for IFNs, in CEFs and DEFs. Conclusion: Results show distinct expression patterns of cytokines, Toll-like receptors and IFNs associated with inflammatory immune responses to NDV between species and by virulence.