By analyzing the residue frequency map, more peaks are revealed than those obtained from the mouse anitsera, with the largest one with its FWHM spanning residues 22-125 with a small split around residue 60, and a medium one with its FWHM at residues 303-350 (Fig. 4 , panel C, and Fig. S4 ). In the structural frequency map (Fig. 4 , panel D), the largest peak is composed of two independent regions: residues 22-60 at the N-terminus of HA1 adjacent to helix A on HA2, designated as R3; and residues 61-125 located in the vestigial esterase domain of the globular head, designated as R5 (indicated by two red regions in the globular head and stem region, respectively, see also In order from most membrane proximal to distal: R1 (orange, residues 424-480 of HA) and R2 (yellow, residues 387-423) in HA2 were determined by screening against mouse and human antisera; R3 (purple, residues 22-60), R4 (green, residues 303-350), and R5 (cyan, residues 61-125) in HA1 were determined by screening against goat antisera. The HA monomer cartoon view is shown on the right and follows the same coloring scheme, with the third monomer shown in the back and colored in grey. doi:10.1371/journal.pone.0018016.g005 should be noticed that R1 and R2 identified in the mouse serum screening also appear in this residue frequency map, although in a much less dominant manner as illustrated by the small plateau between the end of R4 and residue 479 (Fig. 4, panel C) . Taken together, the antigenic peptides recognized by the goat antisera are different from those recognized by the mouse antisera, and in particular present a more diverse picture of antigenic sites in the HA1 region.