Figure 1.

Antigenicity-altering effects of protein sites on the influenza A/H3N2 HA surface. (A) Location of the five epitope regions A–E, colored according to the legend. (B) Inferred antigenic weights for residues on the surface of the HA1 chain of HA protein for human influenza A/H3N2 viruses. The value of the weight is shown with a blue–red gradient for one subunit of the HA homotrimer in three different orientations. The globular head is indicated in yellow; HA2 is colored dark gray. It is evident that not all epitope sites have large antigenic weights and that sites with large antigenic weights are mostly found as spatial clusters within the epitope sites and not outside the epitopes. Sites with antigenic weights outside of the head are not supported by the known biology of the antibody–HA interactions and any likely antigenic hitchhikers found in genotype–phenotype inference.