Western blot analysis was used to determine the specificity of the epitopes present in the peptides P3, P5, and P31. The H1-H16 recombinant HA proteins were obtained by transient expressions of corresponding genes by the pCAGGS vector in 293T cells. The lysates of these cells were used to examine the specificity of antibodies elicited by peptide-conjugates. As shown in Fig. 3A , the anti-P3 serum reacted with H1 (including 07H1 and 09H1 viruses), H2, H5, and H6 HA proteins, while anti-P5 and anti-P31 sera only reacted with the H1 HA proteins. These findings indicated that P5 and P31 may contain H1-subtype specific epitopes.