Figure 5. Antibody responses and protection against lethal challenge.

(A–E) Antibody titers elicited by vaccination with DM-C. Six mice per groups were vaccinated with various doses of DM-C, or mock-infected with PBS as a control. Three weeks after the vaccinations, sera, BALF, and nasal turbinates were collected from the mice. PR8 virus-specific serum IgG (A), HI (B), and viral neutralizing (NT) antibody (C), as well as mucosal secretory IgA antibodies in BALF (D), and nasal turbinates (E) were quantified. Each value was plotted individually in the panel, with the mean of each cohort shown as a line. Dashed horizontal lines indicate the detection limits of each assay. (F) Protection against lethal challenge with WT virus. The vaccinated mice and PBS control groups were challenge with 10 MLD₅₀ of WT viruses at four weeks after the vaccination. Their body weights (left) and survival rates (right) following the challenge were monitored daily.