Abstract
Two surface glycoproteins of influenza virus, haemagglutinin (HA) and neuraminidase (NA), play opposite roles in terms of their interaction with host sialic acid receptors. HA attaches to sialic acid on host cell surface receptors to initiate virus infection while NA removes these sialic acids to facilitate release of progeny virions. This functional opposition requires a balance. To explore what might happen when NA of an influenza virus was replaced by one from another isolate or subtype, in this study, we generated three recombinant influenza A viruses in the background of A/PR/8/34 (PR8) (H1N1) and with NA genes obtained respectively from the 2009 pandemic H1N1 virus, a highly pathogenic avian H5N1 virus, and a lowly pathogenic avian H9N2 virus. These recombinant viruses, rPR8-H1N1NA, rPR8-H5N1NA, and rPR8-H9N2NA, were shown to have similar growth kinetics in cells and pathogenicity in mice. However, much more rPR8-H5N1NA and PR8-wt virions were released from chicken erythrocytes than virions of rPR8-H1N1NA and rPR8-H9N2NA after 1 h. In addition, in MDCK cells, rPR8-H5N1NA and rPR8-H9N2NA infected a higher percentage of cells, and induced cell-cell fusion faster and more extensively than PR8-wt and rPR8-H1N1NA did in the early phase of infection. In conclusion, NA replacement in this study did not affect virus replication kinetics but had different effects on infection initiation, virus release and fusion of infected cells. These phenomena might be partially due to NA proteins’ different specificity to α2-3/2-6-sialylated carbohydrate chains, but the exact mechanism remains to be explored.
Highlights
Influenza A viruses are single-stranded RNA viruses of the family Orthomyxoviridae, containing a segmented genome composed by eight RNA segments
The mortality rate of people suffering from highly pathogenic avian influenza virus infection was high [4],but person-to-person transmission of H5N1 virus was very rare and has been limited so far
The three viruses were successfully rescued by the eight-plasmid reverse genetics system, and they were named rPR8-H5N1NA, rPR8-H1N1NA, rPR8-H9N2NA
Summary
Influenza A viruses are single-stranded RNA viruses of the family Orthomyxoviridae, containing a segmented genome composed by eight RNA segments. The 2009 swine origin pandemic (S-H1N1) influenza virus caused mostly mild influenza-like illness, and the small percentage of severe cases occurred primarily among the young and the middle-aged [5] This virus has displayed apparently higher transmissibility among humans than seasonal influenza viruses and H5N1 viruses have. Christophe et al made an early assessment of transmissibility of S-H1N1 and case severity by analyzing the outbreak in Mexico, early data on international spread, and genetic diversity of the virus They gave an estimated case fatality ratio of 0.4% (range: 0.3 to 1.8%) based on confirmed and suspected deaths reported by late April, 2009 [6]. It is not yet possible to predict the extent of prevalence and severity of illness in humans caused by an influenza virus from its subtype, and the mechanism for virulence acquisition has not been well understood
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