Adaption of Seasonal H1N1 Influenza Virus in Mice

Lili Xu,Hua Zhu,Linlin Bao,Yanfeng Xu,Yila Ma,Fengdi Li,Wei Deng,Chuan Qin,Yuelong Shu,Jiangfang Zhou,Chunmei Ma,Lingjun Zhan,Qi Lv

doi:10.1371/journal.pone.0028901

Abstract

The experimental infection of a mouse lung with influenza A virus has proven to be an invaluable model for studying the mechanisms of viral adaptation and virulence. The mouse adaption of human influenza A virus can result in mutations in the HA and other proteins, which is associated with increased virulence in mouse lungs. In this study, a mouse-adapted seasonal H1N1 virus was obtained through serial lung-to-lung passages and had significantly increased virulence and pathogenicity in mice. Genetic analysis indicated that the increased virulence of the mouse-adapted virus was attributed to incremental acquisition of three mutations in the HA protein (T89I, N125T, and D221G). However, the mouse adaption of influenza A virus did not change the specificity and affinity of receptor binding and the pH-dependent membrane fusion of HA, as well as the in vitro replication in MDCK cells. Notably, infection with the mouse adapted virus induced severe lymphopenia and modulated cytokine and chemokine responses in mice. Apparently, mouse adaption of human influenza A virus may change the ability to replicate in mouse lungs, which induces strong immune responses and inflammation in mice. Therefore, our findings may provide new insights into understanding the mechanisms underlying the mouse adaption and pathogenicity of highly virulent influenza viruses.

Highlights

Seasonal influenza A viruses can cause acute respiratory infections with high morbidity and considerable mortality, in children and the elderly [1]
Some mice inoculated with MA-6 were dead while all of the mice inoculated with MA-8 died or were in agonal states, accompanied by defuse inflammation in the lungs and increasing viral titers to 8.78-8.62 log10 plaque-forming units (PFU)/g, indicating high virulence and pathogenicity (Table 1 and Fig. 1)
Mice are not naturally infected with seasonal H1N1 influenza viruses, many strains of mice can be infected with human strains of influenza viruses, which can be adapted to the mouse by serial lung passage [6]

Summary

Introduction

Seasonal influenza A viruses can cause acute respiratory infections with high morbidity and considerable mortality, in children and the elderly [1]. Experimental infection of mouse lungs with influenza virus has provided insights into understanding viral pathogenicity and adaption [5]. The changes in the viruses during mouse adaptation may provide new insights into understanding factors contributing to the development of virusrelated lung inflammation in humans. Adaption of human influenza virus to mice by serial passages can result in genetic variants with the mutations in multiple genes, such as hemagglutinin (HA), which is a primary factor of mouse lung virulence because of its receptor binding and host membrane fusion activities [8,9,10,11,12,13], and other genes for M, PA, PB1, PB1-F2, PB2, and NS1 [12,13,14,15,16,17,18,19,20,21,22, 23,24]. Further studies indicate that the increased virulence to mice is controlled by both mutations, whereas the enhanced replication in MadinDarby canine kidney (MDCK) cells is attributed to the mutation in the matrix protein [13]

Methods

Results

Conclusion