Tropism and innate host responses of a novel avian influenza A/H5N6 virus in ex vivo and in vitro models of the human respiratory tract

Abstract

Background: H5N6 virus was detected in chickens and ducks in China since 2013 and the first human H5N6 infection was reported in April 2014 in Sichuan, China with fatal outcome. Until now, nine severe human H5N6 infections was confirmed and only 3 patients were recovered from the infections. The aim of this study was to investigate the tropism and pathogenesis of this novel avian influenza virus using ex vivo and in vitro cultures of the human respiratory tract. Method: We compared the virus tropism and innate host responses of the novel H5N6 viruses (both human and wild bird isolates) with that of HPAI H5N1 and 2009 pandemic H1N1 (H1N1pdm). Ex vivo cultures of human nasopharynx, bronchus and lung were used for infection to study the tissue tropism and viral replication efficiency. Since cytokine dysregulation was one of the contributing factors to the disease severity of HPAI H5N1 infection in humans, the induction of proinflammatory cytokines and chemokines after influenza H5N6 virus infection in human alveolar epithelial cells was investigated. Results: Human isolate of the H5N6 virus replicated as efficient as H1N1pdm, had a higher replication competence than HPAI H5N1 virus in human bronchus and the ability to infect human nasopharynx ex vivo cultures. The two wild bird isolates of H5N6 replicated to a mediate level between the H1N1pdm and HPAI H5N1 virus in human bronchial tissues. The human H5N6 virus replicated to higher titers than did H5N1, whereas the wild bird isolates replicated to similar titers as HPAI H5N1 in human lung ex vivo cultures. All three H5N6 viruses were less potent inducers of proinflammatory cytokines compared with H5N1 virus. Conclusion: These results suggest that the novel H5N6 viruses are better adapted to infect and replicate in the human conducting and lower airways than HPAI H5N1 virus. The widely circulating H5N6 viruses in poultry and wild birds pose a significant public health threat.