IL6 and infection: To investigate the immunological basis associated with susceptibility and resistance of Pekin ducks, we detected difference in expression levels of pro-inflammatory cytokines (IL-2, IL-6), chemokine (IL-8) and IFN type I and II (IFN-α, IFN-γ) in the liver of ducklings between Z8S2 and Z8R2 flocks following DHAV-3 infection.