Conservation and variation in the hemagglutinins of Hong Kong subtype influenza viruses during antigenic drift.

The nucleotide sequence was determined for the hemagglutinin gene of the Hong Kong subtype influenza strain A/Bangkok/1/79. The amino acid sequence predicted from these data shows a total of 36 amino acid changes as compared with hemagglutinin for a 1968 Hong Kong strain, 11 more than had occurred in a 1975 strain. The distribution of these changes confirmed that there are conserved and highly variable regions in hemagglutinin as the viral gene evolves during antigenic drift in the Hong Kong subtype. Of the four variable regions found in this study, only two have been seen previously. Correlation of highly variable areas in the hemagglutinins of Hong Kong subtype field strains with sites of amino acid changes in antigenically distinct influenza variants enabled us to predict likely antigenic regions of the protein. The results support and extend similar predictions made recently, based on the three-dimensional arrangement of hemagglutinin from a 1968 influenza strain.