Immune-related gene expression in response to H5N1 avian influenza virus infection in chicken and duck embryonic fibroblasts

Chicken and ducks are important hosts in responses to highly pathogenic avian influenza virus (HPAIV) H5N1 infection. In ducks, avian influenza (AI) generally causes an asymptomatic and long-lasting infection, whereas clinical apparent and transient disease is often observed in chickens. Using real-time quantitative PCR, we examined the expression of immune-related genes in response to H5N1 infection in chicken embryo fibroblasts (CEF) and duck embryo fibroblasts (DEF). While in CEF IL-6 expressed at high levels similar to mammalian species, in DEF expression levels were minimal. Similarly, duck IFN-β expression were slightly upregulated, whereas chicken expressions were highly upregulated. Chronologically, the mRNA levels of both IFN-alpha and IFN-gamma, which belong to type I and type II interferon, respectively, were unregulated in a similar fashion in chickens than in ducks. IL-2 and TLR-7 were elevated from the beginning of the infection in both CEF and DEF to the end of the experiment. Chicken MHC class I expression was almost unaffected while duck expression were downregulated. DEF and CEF MHC class II expression were downregulated. Chemokine IL-8 expression was upregulated in both species. The IL-8 levels closely parallel the IL-1β induced IL-6 levels in the same samples. These results show distinct embryo fibroblasts expression patterns of pro-inflammatory cytokines and IFNs between species.