Restoration of virulence of escape mutants of H5 and H9 influenza viruses by their readaptation to mice

J Gen Virol. 2005 Oct;86(Pt 10):2831-2838. doi: 10.1099/vir.0.81185-0.


Antigenic mapping of the haemagglutinin (HA) molecule of H5 and H9 influenza viruses by selecting escape mutants with monoclonal anti-HA antibodies and subjecting the selected viruses to immunological analysis and sequencing has previously been performed. The viruses used as wild-type strains were mouse-adapted variants of the original H5 and H9 isolates. Phenotypic characterization of the escape mutants revealed that the amino acid change in HA that conferred resistance to a monoclonal antibody was sometimes associated with additional effects, including decreased virulence for mice. In the present study, the low-virulence H5 and H9 escape mutants were readapted to mice. Analysis of the readapted variants revealed that the reacquisition of virulence was not necessarily achieved by reacquisition of the wild-type HA gene sequence, but was also associated either with the removal of a glycosylation site (the one acquired previously by the escape mutant) without the exact restoration of the initial wild-type amino acid sequence, or, for an H5 escape mutant that had no newly acquired glycosylation sites, with an additional amino acid change in a remote part of the HA molecule. The data suggest that such 'compensating' mutations, removing the damaging effects of antibody-selected amino acid changes, may be important in the course of influenza virus evolution.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological / genetics*
  • Animals
  • Antibodies, Viral / blood
  • Antigenic Variation / genetics*
  • Antigens, Viral / chemistry
  • Antigens, Viral / genetics*
  • Antigens, Viral / immunology
  • Hemagglutinin Glycoproteins, Influenza Virus / chemistry
  • Hemagglutinin Glycoproteins, Influenza Virus / genetics*
  • Hemagglutinin Glycoproteins, Influenza Virus / immunology
  • Influenza A virus / classification
  • Influenza A virus / genetics
  • Influenza A virus / immunology
  • Influenza A virus / pathogenicity*
  • Mice
  • Virulence


  • Antibodies, Viral
  • Antigens, Viral
  • Hemagglutinin Glycoproteins, Influenza Virus