The difference between our findings and previously identified epitopes can be explained by the difference of screening method used between our study and those of others. In previous studies, monoclonal antibodies from murine hybridoma cells were used to identify antigenic sites, while in this study we used a peptide scanning approach, which involves overlapping peptide library and human convalescent antisera-a strategy that is widely used for viral epitope identification [27, 42] . Given the fact that viral antigen can be recycled and presented as short peptides with different conformation during humoral immune response and these short peptides can be selected by B cell clones [43] , and that convalescent sera from patients were much more complex than monoclonal antibodies from mice and can reflect the real immune responses during viral infection [44] , our approach adds to the available techniques currently being used to identify linear epitopes in serologic tests. Because HA pseudotyped lentivirus has been widely applied in the study on neutralizing antibodies against IAVs [30] , we used this method to evaluate if the epitopes identified in this study could stimulate neutralizing antibodies. Our data showed that these epitopes could not elicit neutralizing antibodies in pseudovirion neutralizing assays due to their linear nature. Previous studies have shown that most neutralizing epitopes are conformation dependent [34, 35] .