To determine if the epitopes identified in this study can stimulate neutralizing antibodies, a HA-pseudotype neutralization test was performed against the anti-peptide sera using the H1N1pdm pseudotyped lentivirus. None of the sera against P3, P5, P16, and P31 could efficiently inhibit (90% inhibition [30] ) the entry of H1N1pdm HA pseudotypes ( Figure 2D ), indicating that these epitopes do not contain neutralizing activity.