1. Department of Microbiology, University of Washington School of Medicine, Seattle, Washington 98195, USA
2. Influenza Branch, DVRD, NCID, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA
3. Washington National Primate Research Center, Seattle, Washington 98195, USA
4. Department of Microbiology, Mount Sinai School of Medicine, New York, New York 10029, USA
5. Department of Molecular Pathology, Department of Cellular Pathology and Genetics, Armed Forces Institute of Pathology, Rockville, Maryland 20850, USA
6. Southeast Poultry Research Laboratory, Agricultural Research Laboratory, US Department of Agriculture, Athens, Georgia 30606, USA
7. †Present address: Laboratory of Infectious Diseases, NIAID, NIH, Bethesda, Maryland 20892, USA

Correspondence to: John C. Kash¹ Correspondence and requests for materials should be addressed to J.K. (Email: jkash@u.washington.edu). Raw data on expression microarrays are available at http://expression.microslu.washington.edu.

Abstract

The influenza pandemic of 1918–19 was responsible for about 50 million deaths worldwide¹. Modern histopathological analysis of autopsy samples from human influenza cases from 1918 revealed significant damage to the lungs with acute, focal bronchitis and alveolitis associated with massive pulmonary oedema, haemorrhage and rapid destruction of the respiratory epithelium². The contribution of the host immune response leading to this severe pathology remains largely unknown. Here we show, in a comprehensive analysis of the global host response induced by the 1918 influenza virus, that mice infected with the reconstructed 1918 influenza virus displayed an increased and accelerated activation of host immune response genes associated with severe pulmonary pathology. We found that mice infected with a virus containing all eight genes from the pandemic virus showed marked activation of pro-inflammatory and cell-death pathways by 24 h after infection that remained unabated until death on day 5. This was in contrast with smaller host immune responses as measured at the genomic level, accompanied by less severe disease pathology and delays in death in mice infected with influenza viruses containing only subsets of 1918 genes. The results indicate a cooperative interaction between the 1918 influenza genes and show that study of the virulence of the 1918 influenza virus requires the use of the fully reconstructed virus. With recent concerns about the introduction of highly pathogenic avian influenza viruses into humans and their potential to cause a worldwide pandemic with disastrous health and economic consequences, a comprehensive understanding of the global host response to the 1918 virus is crucial. Moreover, understanding the contribution of host immune responses to virulent influenza virus infections is an important starting point for the identification of prognostic indicators and the development of novel antiviral therapies.

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