Poster Session: News and Views from H7N9 OutbreakBackground: As of May 2013, 131 laboratory-confirmed human infections with a novel influenza H7N9
virus had been reported from China. The source of human infection appears to be poultry. There is so
far no evidence of sustained human-to-human transmission. Genetic analysis revealed that all eight
gene segments of H7N9 were of avian origin; six internal gene segments from avian influenza H7N9
viruses, while hemagglutinin and neuraminidase genes were derived from influenza viruses circulating
in ducks and wild ducks, respectively. The emergence of the H7N9 influenza virus catches global
attention about whether the new virus could spark another pandemic. The majority of the infected
patients were hospitalized and suffered from ARDS, with a fatality rate of about 37%. Our study aimed
to determine the mechanism contributing to the pathogenesis of the H7N9 virus. A panel of
proinflammatory cytokines and chemokines will be examined upon influenza H7N9 virus infection in
alveolar epithelial cells in order to examine if these mediators were induced differentially when
compared with the highly pathogenic avian influenza (HPAI) H5N1 and the 2009 pandemic H1N1
virus. Moreover, because cleaved caspase 3 is commonly employed as a marker for the indication of
apoptosis, we further examined the extensiveness of cleaved caspase 3 in influenza virus infection in human lung ex vivo cultures. Materials and Methods: Fresh biopsies of human lung tissue were
obtained from patients undergoing surgical resection of lung tissues. Lung tissue fragments were
cultured with F12K medium incubated at 37°C. For viral infection experiments, influenza viruses
A/Shanghai/1/2013 (SH1, H7N9), A/Shanghai/2/2013 (SH2, H7N9), A/Hong Kong/483/97 (H5N1),
and A/California/07 (Ca07, H1N1pdm) at a viral titer of 106 TCID50/mL were used for ex vivo lung
culture infection. Infected lung tissues were collected in 10% formalin at 24, 48, and 72 hpi for
immunohistochemical staining. Costaining of cleaved caspase 3 and influenza virus nucleoprotein
was carried out for the detection of apoptosis. Furthermore, primary culture of human alveolar
epithelial cells was isolated from human lungs by mincing the lung, followed by filtration and
centrifugation. Human alveolar epithelial cells were infected with the novel influenza H7N9, the HPAI
H5N1, and the pandemic H1N1 virus. Virus replication was monitored by measuring infectious viral
particles using TCID50. mRNA and protein expression of proinflammatory cytokines and chemokines
were quantified by real time qPCR and ELISA. Results: We found extensive apoptosis in influenza
H7N9 (both SH1 and SH2) and H5N1, but not H1N1pdm infected ex vivo lung tissues, suggesting that
both avian influenza viruses can induce apoptosis and cause severe cell death in human lung tissue.
Furthermore, unlike HPAI H5N1 which induces dysregulated proinflammatory cytokine responses, the
novel influenza H7N9 virus elicited poor proinflammatory cytokine responses, inducing type I and III
interferon in ex vivo human lung explant cultures. The novel influenza H7N9 virus is an intrinsically
more potent inducer of proinflammatory cytokine than the H1N1pdm virus but less than the H5N1
virus. Conclusions: The proinflammatory cytokine and chemokine responses may contribute modestly
to the severity of human H7N9 disease, but it is likely that direct viral cytopathology is probably
playing a more important role in pathogenesis of human H7N9 diseases. The recognition of the role of
cleaved caspase 3 in severe human infection of avian influenza virus can provide insights on the
development of novel therapeutic approaches for the preparedness of the future outbreak of
pandemics.published_or_final_versio
