Differential innate responses of chickens and ducks to low-pathogenic avian influenza

Ducks and chickens are hosts of avian influenza virus, each with distinctive responses to infection. To understand these differences, we characterized the innate immune response to low pathogenicity avian influenza virus H7N1 infection in chickens and ducks. Viral RNA was detected in the lungs of chickens from day 0.8 to 7, in ducks mainly at day 4. In both species viral RNA was detected in the bursa and gut. Infection in chickens resulted in up-regulation of interferon (IFN)-a and IFN-ß mRNA, while in the ducks IFN-¿ mRNA was strongly up-regulated in lung and bursa. In chickens and ducks all investigated pathogen recognition receptors (PRR) mRNA were up regulated, however, in the chicken lung Toll-like receptor (TLR)7 and melanoma differentiation-associated protein (MDA)-5 mRNA were strongly induced. TLR3, TLR7 and MDA-5 responses correlated with IFN-a and IFN-ß responses in chickens, but in ducks a correlation between IFN-a and TLR7, retinoic acid-inducible gene-I and MDA-5 was absent. We studied the responses of duck and chicken splenocytes to poly (I:C) and R848 analogues to analyze the regulation of PRRs without the interfering mechanisms of the influenza virus. This revealed IFN-a and IFN- ¿ responses in both species. MDA-5 was only strongly up-regulated in chicken splenocytes. In chickens splenocytes, time related PRR responses correlated with the IFN-a and IFN-ß response. In duck splenocytes this correlation was absent. In conclusion, chicken and duck differ in induction of MDA-5, TLR7 and IFN-a mRNA after an influenza virus infection in vivo and after in vitro stimulation with TLR antagonists.