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Interference is controlled by segment 2 and possibly by segment 8 of the nondefective interfering influenza virus
E G Brown1, C F Dimock, K Hannah
1Department of Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ontario, Canada.
Abstract:
On mouse adaption of A/FM/1/47, a variant, A/FM/1/47-MA (FM-MA), that had acquired the properties of increased virulence and interference was produced. Coinfection of cells with FM-MA and prototype strains of influenza virus yielded > 100-fold more FM-MA virus than prototype virus, whereas coinfection with the same prototype strains and the parental A/FM/1/47 virus produced equivalent yields, indicating that FM-MA had acquired mutations that confer the property of interference during mouse adaption. FM-MA is a nondefective interfering virus that grows to a high titer in vivo and in vitro. It has previously been shown that segments 4, 7, and 8 and possibly segment 5 account for the increased virulence. In this study we show by genetic analysis of FM-MA x A/HK/1/68 reassortants that segment 2, coding for the polymerase-associated protein PB1, and possibly segment 8, encoding the NS1 and NS2 proteins, control the ability of FM-MA to interfere. Interference could not be overcome by increasing the titer of the coinfecting strain, but delaying FM-MA infection by 4 to 6 h did avoid interference. During interference of A/HK/1/68, protein synthesis was inhibited by less than 65% throughout coinfection. Given the kinetics of interference and the small perturbation in protein synthesis, interference appeared to occur at the level of late genome replication or virus assembly. Virulence and interference in FM-MA were not linked. An interfering avirulent FM-MA x A/HK/1/68 reassortant, E07, was capable of protecting mice against lethal pneumonia due to a virulent noninterfering reassortant, H04.
Insights
Mouse-adapted influenza A/FM/1/47-MA (FM-MA) exhibits increased virulence and interference. Genetic analysis revealed that viral segment 2 (PB1) and segment 8 (NS1/NS2) control FM-MA
Area of Science:
- Virology
- Molecular Biology
- Immunology
Background:
- Influenza A virus adaptation in mice can lead to variants with altered properties.
- A/FM/1/47-MA (FM-MA) is a mouse-adapted variant of influenza A/FM/1/47.
- Previous studies identified viral segments 4, 7, and 8, and possibly 5, contributing to FM-MA's increased virulence.
Purpose of the Study:
- To elucidate the genetic basis of interference in the FM-MA influenza virus.
- To investigate the relationship between virulence and interference in FM-MA.
- To assess the protective potential of interfering FM-MA reassortants.
Main Methods:
- Genetic analysis of reassortant viruses derived from FM-MA and A/HK/1/68.
- Coinfection experiments to assess viral yields and interference.
- Evaluation of protein synthesis inhibition during coinfection.
- Assessment of protection against lethal influenza pneumonia in mice.
Main Results:
- Segment 2 (PB1) and possibly segment 8 (NS1/NS2) of FM-MA control its interference property.
- Interference was not overcome by increasing coinfecting virus titer but could be avoided by delayed infection.
- Protein synthesis inhibition was minimal (<65%) during interference, suggesting a late-stage replication or assembly block.
- Virulence and interference were found to be unlinked traits.
- An interfering avirulent reassortant (E07) protected mice against a virulent noninterfering reassortant (H04).
Conclusions:
- Influenza virus interference is primarily controlled by segment 2 (PB1) and segment 8 (NS1/NS2) in the FM-MA variant.
- Interference occurs at late stages of viral replication or assembly.
- Separation of virulence and interference provides opportunities for developing live attenuated vaccines.