Figure 3. Hemagglutination inhibition (HAI) antibody responses in rabbit sera immunized with different designed H7-HA DNA vaccines (H7-HA-wt, H7-HA-tPA, and H7-HA-dTM) in rabbits. HAI antibody responses were measured against a wild type H7N1 virus (A/African Starling/England-Q/938/79) (A) or H7N1 pseudovirus expressing H7-HA from A/Netherlands/219/03 (H7N7) and H1 N1-NA from A/VietNam/1203/04 (H5N1) (B). The rabbit sera used in the HAI assay were collected at 2 wk after the fourth DNA immunization or relevant pre-bleed sera, as indicated. HAI antibody titers are shown as the geometric mean for each group (3 rabbits per group) with standard deviations. Statistical significance (P < 0.05) between vaccine groups is indicated.