Influenza virus with increased pH of HA activation has improved replication in cell culture but at the cost of infectivity in human airway epithelium.
Author(s)
Singanayagam, Anika
Zambon, Maria
Barclay, Wendy
Type
Journal Article
Abstract
Pandemic H1N1 (pH1N1) influenza virus emerged from swine in 2009 with adequate capability to infect and transmit between people. In subsequent years it has circulated as a seasonal virus and evolved further human-adapting mutations. Mutations in the haemagglutinin (HA) stalk that increase pH stability have been associated with human adaptation and airborne transmission of pH1N1 virus. Yet, our understanding of how pH stability impacts virus/host interactions is incomplete. Here, using recombinant viruses with point mutations that alter the pH stability of pH1N1 HA, we found distinct effects on virus phenotypes in different experimental models. Increased pH sensitivity enabled virus to uncoat in endosomes more efficiently, manifesting as increased replication rate in typical continuous cell cultures under single-cycle conditions. A more acid labile HA also conferred a small reduction in sensitivity to antiviral therapeutics that act at the pH-sensitive HA fusion step. Conversely, in primary human airway epithelium cultured at air-liquid interface, increased pH sensitivity attenuated multicycle viral replication, by compromising virus survival in the extracellular microenvironment. In a mouse model of influenza pathogenicity, there was an optimum HA activation pH and viruses with either more or less pH stable HA were less virulent. Opposing pressures inside and outside the host cell that determine pH stability may influence zoonotic potential. The distinct effects that changes in pH stability exert on viral phenotypes underscore the importance of using the most appropriate systems for assessing virus titre and fitness, which has implications for vaccine manufacture, antiviral drug development and pandemic risk assessment.ImportanceThe pH stability of the haemagglutinin surface protein varies between different influenza strains and subtypes and can affect the virus' ability to replicate and transmit. Here, we demonstrate a delicate balance the virus strikes within and without the target cell. We show that a pH-stable haemagglutinin enables a human influenza virus to replicate more effectively in human airway cells and mouse lungs by facilitating virus survival in the extracellular environment of the upper respiratory tract. Conversely after entering target cells, being more pH-stable confers relative disadvantage, resulting in less efficient delivery of the viral genome to the host cell nucleus. Since the balance we describe will be affected differently in different host environments, it may restrict virus' ability to cross species. In addition, our findings imply that different influenza viruses may show variation in how well they are controlled by antiviral strategies targeting pH-dependent steps in the virus replication cycle.
Date Issued
2019-09-01
Date Acceptance
2019-06-02
Citation
Journal of Virology, 2019, 98 (17)
ISSN
0022-538X
Publisher
American Society for Microbiology
Journal / Book Title
Journal of Virology
Volume
98
Issue
17
Copyright Statement
© 2019 Singanayagam et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0/)
Sponsor
Wellcome Trust
Identifier
https://www.ncbi.nlm.nih.gov/pubmed/31189708
PII: JVI.00058-19
Grant Number
105736/Z/14/Z
Subjects
Science & Technology
Life Sciences & Biomedicine
Virology
influenza
hemagglutinin
viral replication
virology
A VIRUS
STEM REGION
HA STEM
FUSION
TRANSMISSION
ADAPTATION
MUTATIONS
GROWTH
ACID
INHIBITORS
hemagglutinin
influenza
viral replication
virology
Virology
06 Biological Sciences
07 Agricultural and Veterinary Sciences
11 Medical and Health Sciences
Publication Status
Published
Coverage Spatial
United States
Article Number
00058-19
Date Publish Online
2019-08-13