Antibody binding to a hemagglutinin panel from diverse H5N1 influenza virus clades. Binding was assessed in an antigen down format, where HA was immobilized on a plate (A, C), or in an MAb down format, where the MAb was immobilized on a plate (B, D, E). Binding of the FcDART molecule (F) was measured in an antibody down format, with FcDART being captured with anti-human IgG Fc-specific polyclonal antibody. OD, optical density.