Epitope mapping of neutralizing monoclonal antibody in avian influenza A H5N1 virus hemagglutinin

► We produced a neutralizing antibody against clade 1 of H5 influenza virus. ► The antibody recognized the loop at amino acid positions 140-145 of HA1. ► The amino acids at 142, 144, and 145 were critical for the antibody recognition. ► The antibody cross-neutralized the clade 2.2.1 but not clade 2.1.3.2 or 2.3.4 of H5 virus. ► The amino acids at 142 and 145 were conserved in the clade 2.2.1 virus.