Comparison of antigenic differences in the HA structures of 1918, Cal/09 and Bris/59/07 viruses.

<p>(A) Ribbon representation of an HA monomer (H1 and H2) of the three viruses. Individual antigenic sites are highlighted by green ellipses in the HA monomers. (B) Top panel: Zenithal surface top view of HA trimeric complexes depicting antigenic sites and their differences among 1918, Cal/09 and Bris/59/07 viruses. Blue color corresponds to conserved amino acids and red color represents amino acids that differ from 1918 HA. The antigenic sites are colored in light blue. Bottom panel: Close-up view of antigenic site Sa in monomeric 1918 and Cal/04 HAs. Amino acids K171, G172 and K180 (K157, G158 and K166 by H3 numbering) corresponding to mAb escape mutations are shown in yellow.