Innate immune response-related gene expression profiles in chickens infected with either CEF-H9N2 or MDCK-H9N2. At 1, 3, and 5 dpi, trachea, duodenum, and spleen tissues were resected from chickens infected with CEF-H9N2 or MDCK-H9N2 and mRNA levels of TLR-7 (A), TLR-3 (B), IFN-α (C), IFN-β (D), IFN-γ (E), IL-6 (F), and IL-1β (G) were detected in each by RRT-PCR. Fold-changes in gene expression were calculated relative to the corresponding levels detected in non-challenged chickens. Data were normalized to GAPDH expression, calculated according to the 2−∆∆Ct method , and expressed as mean ± standard deviation. An asterisk indicates statistically significant differences between the two clones (P < 0.05).