Figure 1
The contribution of HA gene amino acid mutations to antigenic variation. A The location of the amino acid mutations in the three-dimensional structure of HA protein of H9N2 subtype avian influenza virus. The yellow colour indicates the locations of the HA receptor binding sites, including positions 128–132, 91, 143, 145, 173, 180, 284, 185, and 214–219. The pink colour (positions 115, 127, 146, 150, 180 and 216) indicates mutations on antigenic sites that have been reported. The red colour (positions 113, 163, 26, 252, 256, 260, 368 and 381) indicates mutations that have not been previously reported as antigenic sites. B, C The HI titres of the F/98 immune sera from chickens (n = 8) to each recombinant virus, (B) with single mutants in HA from passaged viruses undergoing antigenic drift in embryonated chicken eggs or chickens, or (C) with multiple mutants in HA from passaged viruses occurring in the 47th generation in embryonated chicken eggs under selective pressure on antibodies. *A ≥ fourfold change in HI titres of the standard antiserum was considered a significant antigenic change.