Passage in egg culture is a major cause of apparent positive selection in influenza B haemagglutinin.

Derek Gatherer (1)

1 MRC Virology Unit

Several studies have identified residues apparently under positive selection in influenza B virus haemagglutinin. Host immune evasion is the main mechanism proposed to exert this selection pressure. However, these reports have not considered the culture history of the strains used to calculate positive selection. This paper shows that passage of influenza B virus through egg culture is a strong contributory factor to the strength and statistical significance of positive selection on haemagglutinin. Non-synonymous mutations resulting in the loss of the N-glycosylation site at positions 197-199 of haemagglutinin have been positively selected to a far greater degree in egg-cultured strains than in other strains. Once egg-cultured strains are removed from the analysis, positive selection is found to be far weaker, less statistically significant and more diffusely localised along the protein. Caution should therefore be exercised both in claims for the existence of positive selection in influenza B haemagglutinin, and in attribution of host immune evasion as its cause. The major cause of molecular adaptation in influenza B haemagglutinin proteins may well be laboratory eggs rather than natural hosts.

Mots clés: Medicine

Derek Gatherer. Passage in egg culture is a major cause of apparent positive selection in influenza B haemagglutinin.. Journal of Medical Virology, 2009, 82 (1), pp.123. ⟨10.1002/jmv.21648⟩. ⟨hal-00541147⟩