Imbalanced Inflammatory Response Human Endothelial Cells Resulting in a H 5 N 1 Virus Activates Signaling Pathways in Wittkowski , Stephan Ludwig and Johannes Roth

H5N1 influenza virus infections in humans cause a characteristic systemic inflammatory response syndrome; however, the molecular mechanisms are largely unknown. Endothelial cells (ECs) play a pivotal role in hyperdynamic septic diseases. To unravel specific signaling networks activated by H5N1 we used a genome-wide comparative systems biology approach analyzing gene expression in human ECs infected with three different human and avian influenza strains of high and low pathogenicity. Blocking of specific signaling pathways revealed that H5N1 induces an exceptionally NF-kB–dependent gene response in human endothelia. Additionally, the IFN-driven antiviral program in ECs is shown to be dependent on IFN regulatory factor 3 but significantly impaired upon H5N1 infection compared with low pathogenic influenza virus. As additional modulators of this H5N1-specific imbalanced gene response pattern, we identified HMGA1 as a novel transcription factor specifically responsible for the overwhelming proinflammatory but not antiviral response, whereas NFATC4 was found to regulate transcription of specifically H5N1-induced genes. We describe for the first time, to our knowledge, defined signaling patterns specifically activated by H5N1, which, in contrast to low pathogenic influenza viruses, are responsible for an imbalance of an overwhelming proinflammatory and impaired antiviral gene program. I nfluenza A viruses still pose a major threat due to their pandemic potential. There is a huge natural virus reservoir in birds, which provides a pool of viral genes that contribute to the generation of novel pandemic virus strains. The highly path-ogenic avian H5N1 virus is the first example of an avian virus reported to have infected and killed several hundreds of humans (1). Human-adapted influenza A viruses cause primarily infections of the upper respiratory tract with limited virus replication. Highly pathogenic avian influenza viruses (HPAIVs) rather cause systemic infections with hemorrhagic sepsis in poultry. In humans, clinical manifestations of H5N1 infections are a systemic inflammatory response syndrome (SIRS) leading to multiorgan failure (2–6). There are two characteristics of H5N1 infections: an unusual strong cytokine response (7, 8) and a neuro-as well as endothelial cell (EC) tropism (9–13). Recently, a-2,3-linked sialic acid receptors preferentially bound by avian influenza virus were shown to be present on human ECs, suggesting a crucial involvement of ECs in the characteristics of systemic H5N1 diseases (14). Isolated suppression or knockdown of the cytokine response did not protect against lethal outcomes (13, 15, 16). In human bronchial epi-thelial cells, high pathogenic H5N1 variants replicate stronger than low pathogenic variants or the human H3N2 virus but …