Multifunctional adaptive NS1 mutations are selected upon human influenza virus evolution in the mouse

Area of Science:

• Virology
• Immunology
• Molecular Biology

Background:

• Influenza A virus virulence and host range are influenced by viral proteins.
• The NS1 protein is known to play a role in counteracting host antiviral defenses.

Purpose of the Study:

• To investigate the role of NS1 protein mutations in modulating influenza A virulence and host adaptation.
• To identify specific NS1 mutations that enhance viral replication and pathogenicity in a mouse model.

Main Methods:

• Adaptation of A/Hong Kong/1/1968 (H3N2) influenza A virus to increased virulence in mice.
• Sequencing of the NS genome segment to identify mutations in NS1 and NEP genes.
• Reverse genetics to introduce mutant NS gene segments into the virus and assess phenotypic changes.

Main Results:

• All identified NS1 mutations were adaptive, enhancing virus replication in mouse cells and lungs (up to 100-fold).
• Most NS1 mutants increased virulence in mice, evidenced by reduced survival and weight loss.
• Mutant NS1 proteins enhanced interferon-beta (IFN-β) antagonism, reducing IFN-β production and increasing viral yields in infected lungs.

Conclusions:

• The NS1 protein is a multifunctional virulence factor that undergoes adaptive evolution.
• NS1 mutations contribute significantly to influenza A virus virulence by enhancing replication and immune evasion.
• Further studies are needed to assess the contribution of NEP mutations to observed phenotypic changes.