Figure 3. Immunization of mice with PA admixed with liposomes with different net charges induced strong and functional PA-specific antibody responses.

BALB/c mice (n = 5) were dosed with PA admixed with liposomes (DOPC, DOTAP, or DOPA) on days 0 and 14. Control mice were injected with PA admixed with Alum or PBS alone. Mice were bled on day 26.

A. Anti-PA IgG levels in mouse serum samples.

B. The anti-PA antiserum protected mouse macrophages from anthrax lethal toxin challenge. Mouse serum samples were diluted 10-fold serially, and incubated with J774A.1 cells in the presence of anthrax lethal toxin. The neutralization activity was determined with 3 replicates.

C, D. Serum anti-PA IgG1 and IgG2a levels.

E. Serum anti-PA IgG level in mice immunized with PA in PBS or PA admixed with Alum (PA/Alum, 5 µg/50 µg). Data reported are mean ± SD (n = 5 except in E where n = 4 or 5). In A, * p < 0.003, PA/Alum vs. PA/DOPA. For PA/DOTAP vs. PA/DOPA, p = 0.18, 0.07, 0.05 at 100-, 1,000-, and 10,000-fold dilutions, respectively. At 10,000-fold dilution, PA/Alum is not different from PBS (p = 0.10). In E, the values of the PA/Alum and PBS were different (p < 0.05), except at 640,000-fold dilution.