Figure 4. Results of matrix protein 2 (M2) vaccination and booster with DNA prime–adenovirus (Ad), showing cross-reactive antibodies. Mice (8–10 per group) were vaccinated with DNA and given an Ad booster as described in Methods. Immune serum collected 3 weeks after the booster was assayed for immunoglobulin (Ig) G reactive to various M2e peptides by ELISA, as described in Methods. Plates were coated with M2e-PR8 (panel A), M2e-FM (panel B), M2e-H5(SP-83) (panel C), or M2e-H5(HK) (panel D). OD, optical density.