Attenuation of an influenza A virus due to alteration of its hemagglutinin-neuraminidase functional balance in mice
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Influenza A viruses possess two surface glycoproteins, hemagglutinin (HA), which binds to sialic-acid-containing receptors, and neuraminidase (NA), which removes sialic acid from host cells. It is well established that the HA-NA functional balance regulates the efficiency of virus replication. Here, we selected a plaque variant of the WSN (H1N1) strain that grew better than the wild-type virus in NA-expressing MDCK cell culture. A reverse genetics study revealed that the single mutation HA E190K, which occurs infrequently in naturally isolated H1N1 viruses, was responsible for the phenotype of this variant. Receptor assays indicated that this mutation did not affect the receptor specificity of HA but enhanced its receptor-binding affinity, resulting in altered HA-NA functional balance relative to that of the wild-type virus. We also found that this variant replicated in nasal turbinates at an equivalent level but in lungs at a lower level compared with wild-type virus, demonstrating its attenuation in mice. Together, our data demonstrated the importance of the HA-NA functional balance for influenza virus replication in an in vivo biological setting.
KeywordsSialic Acid H1N1 Virus MDCK Cell Parent Virus Large Plaque
We thank Dr. Emi Takashita and Susan Watson for providing anti-NA antibody and editing the manuscript. This work was supported by grants-in-aid for Specially Promoted Research and for Scientific Research (B), from the Ministry of Education, Culture, Sports, Science, and Technology, by grants-in-aid from the Ministry of Health, Labor and Welfare, by ERATO, and by National Institute of Allergy and Infectious Diseases Public Health Service research grants.
Conflict of interest
The authors declare that they have no conflicts of interest
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