Infected chicken and duck cells showed differential regulation of STAT-3 . IFN-α expression was significantly up-regulated in chicken (A) and duck (B) cells at 24 h following infection with LPAI-H2N3, H5N1-tyEng91 or H5N1-tyTR05 viruses. (C) While STAT-3 expression in chicken cells was not significantly affected by LPAI-H2N3 virus infection it was significantly down-regulated in H5N1-tyEng91 and H5N1-tyTR05 virus infections. (D) In contrast STAT-3 expression in duck cells was significantly up-regulated by LPAI-H2N3 or H5N1-tyEng91 viruses but was not affected by H5N1-tyTR05 virus infection. 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 (*p < 0.05). (E) Strong constitutive phospho-STAT-3 protein expression was detected in duck cells which was unaffected at 24 h following infection with H5N1-tyEng91 and H5N1-tyTR05 viruses. In chicken mock-infected cells, phospho-STAT3 protein expression was scarcely detectable and remained absent at 24 h following virus infection. aLonger (5 min) exposure showing pSTAT-3 in chicken cells.