Evolutionary dynamic of antigenic residues on influenza B hemagglutinin.

Hemagglutinin (HA) of seasonal influenza virus evolves under positive selection pressure exerted by host immunity. It was previously shown that antigenic drift in different influenza B sublineages during different time periods distributed unevenly among different epitopes, and that more recent viruses up to 2007 might have their antigenic drift more focused on certain epitope. We further analyzed whether more recent influenza B viruses up to 2016 followed that same pattern of antigenic evolution. By using Shannon entropy and relative entropy to characterize HA antigenic epitopes, the most recent viruses of both Victoria and Yamagata lineages had residues with high relative entropy located most frequently on the 120-loop region. In addition to residues in the known epitopes, possible antigenic residues were also identified outside of the known epitope regions. The data provide an insight into the antigenic evolution of current influenza B viruses and expand our knowledge on their antigenic sites.