Our previous knowledge of viral antigenic structure was based mainly on the structure of antibody-antigen complexes or mutational analysis of related antigenic drifts [6] [7] [8] . Recently, many new approaches have emerged for the rapid extraction of monoclonal antibodies toward target antigens from antibody phage display libraries [5, 9, 10] , using direct sorting of memory B cells [11] , or by immortalization of IgG expressing B cells that reflect the antibody repertoire [12, 13] . These methods provide much more information on viral epitopes, although they are often laborious. The major alternative approaches for epitope mapping are derived from scanning with antigenic peptides displayed on the surface of bacteriophage, bacteria and yeast [14] [15] [16] [17] [18] [19] [20] [21] , which in recent years have increasingly incorporated fluorescence-activated cell sorting (FACS). In these efforts, short defined or random peptides with a narrow length range (,50 amino acid residues (aa)) are used to screen against monoclonal or polyclonal antibodies.