Figure 1. Results of matrix protein 2 (M2)e–keyhole limpet hemocyanin (KLH) vaccination, showing induction of cross-reactive antibody responses. Mice (7–9 per group) were immunized intraperitoneally with KLH or M2e peptides conjugated to KLH (M2e-con/KLH, M2e-FM/KLH, or M2e-H5(HK)/KLH) in complete Freund’s adjuvant. After 21 days, the mice were given an intraperitoneal booster with KLH or M2e-peptide/KLH in incomplete Freund’s adjuvant. Immune serum was collected 13 days after booster and assayed for immunoglobulin (Ig) G reactive to various M2e peptides by ELISA. Plates were coated with M2e-PR8 (panel A), M2e-FM (panel B), M2e-H5(SP-83) (panel C), or M2e-H5(HK) (panel D). Data are representative of multiple experiments. OD, optical density; e, ectodomain.