Pro-inflammatory cytokine gene response to H5N1 virus challenge in chickens and ducks. In the lungs and spleens of 3-weeks-old chickens at 24 h following infection with H5N1-tyTR05 virus, mRNA expression levels of (A) LITAF, (B) IL-6 and (C) IL-8 were significantly up-regulated compared with mock-infected controls. (D) Increased pro-inflammatory gene response in virus infected lungs correlated with RNA accumulation of influenza virus M-gene. In contrast, in the lungs and spleens of 4- weeks- old ducks infected with H5N1-tyTR05 virus, (H) despite viral M-gene RNA detection, (E) LITAF mRNA expression was significantly down-regulated and expression of (F) IL-6 and (G) IL-8 unaffected in relation to mock-infected controls. Relative mRNA expression was determined by real-time PCR normalised to 18S rRNA. Data points are the mean of three biological replicates with error bars as standard deviation.