title: Single gene reassortants identify a critical role for PB1, HA, and NA in the high virulence of the 1918 pandemic influenza virus.
abstract: The 1918 influenza pandemic was exceptionally severe, resulting in the death of up to 50 million people worldwide. Here, we show which virus genes contributed to the replication and virulence of the 1918 influenza virus. Recombinant viruses, in which genes of the 1918 virus were replaced with genes from a contemporary human H1N1 influenza virus, A/Texas/36/91 (Tx/91), were generated. The exchange of most 1918 influenza virus genes with seasonal influenza H1N1 virus genes did not alter the virulence of the 1918 virus; however, substitution of the hemagglutinin (HA), neuraminidase (NA), or polymerase subunit PB1 genes significantly affected the ability of this virus to cause severe disease in mice. The 1918 virus virulence observed in mice correlated with the ability of 1918 recombinant viruses to replicate efficiently in human airway cells. In a second series of experiments, eight 1918 1:7 recombinants were generated, in which each Tx/91 virus gene was individually replaced by a corresponding gene from 1918 virus. Replication capacity of the individual 1:7 reassortant viruses was assessed in mouse lungs and human airway cells. Increased virus titers were observed among 1:7 viruses containing individual 1918 HA, NA, and PB1 genes. In addition, the 1918 PB1:Tx/91 (1:7) virus showed a distinctly larger plaque size phenotype than the small plaque phenotype of the 1918 PA:Tx/91 and 1918 PB2:Tx/91 1:7 reassortants. These results highlight the importance of the 1918 HA, NA, and PB1 genes for optimal virus replication and virulence of this pandemic strain.
authors.affiliation: Influenza Division, Mailstop G-16, National Center for Immunization and Respiratory Diseases, Coordinating Center for Infectious Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road Northeast, Atlanta, GA 30333, USA.
authors.forename: Claudia
authors.initials: C
authors.lastname: Pappas
authors.forename: Patricia V
authors.initials: PV
authors.lastname: Aguilar
authors.forename: Christopher F
authors.initials: CF
authors.lastname: Basler
authors.forename: Alicia
authors.initials: A
authors.lastname: Solórzano
authors.forename: Hui
authors.initials: H
authors.lastname: Zeng
authors.forename: Lucy A
authors.initials: LA
authors.lastname: Perrone
authors.forename: Peter
authors.initials: P
authors.lastname: Palese
authors.forename: Adolfo
authors.initials: A
authors.lastname: García-Sastre
authors.forename: Jacqueline M
authors.initials: JM
authors.lastname: Katz
authors.forename: Terrence M
authors.initials: TM
authors.lastname: Tumpey
mesh_terms: D000818:Animals; D005260:Female; D006389:Hemagglutinins, Viral / Q000235:genetics*; D049673:History, 20th Century; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics / Q000472:pathogenicity*; D007251:Influenza, Human / Q000235:genetics* / Q000266:history*; D008168:Lung / Q000821:virology; D051379:Mice; D008807:Mice, Inbred BALB C; D009439:Neuraminidase / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014764:Viral Proteins / Q000235:genetics*; D014774:Virulence; D014779:Virus Replication / Q000235:genetics*
chemical_list: D006389:Hemagglutinins, Viral; D014764:Viral Proteins; C077346:influenza virus polymerase basic protein 1; C487630:NA protein, influenza A virus; D009439:Neuraminidase