Detection of IgG antibody responses by ELISA in mice immunized with HA1 fusion proteins plus Poly(I:C) or CpG adjuvant. PBS with or without adjuvants was used as the negative control. ELISA plates were coated with HA1-FdFc, HA1-Fc, HA1-Fd, or HA1-His protein, respectively (A), or full-length HA1-His protein (B), and IgG antibody was detected using mouse sera (1:3,200) from 10 days post-last vaccination. The data are presented as A450 ± SD of 4 mice per group. The *, ** and *** indicate the significant difference with P < 0.05, 0.01 and 0.001, respectively, between the groups with or without adjuvants.