FIG. 3.

Comparison of antibody production in lung mucosal secretions between s.c. and i.n. immunization in mice and guinea pigs. Animals were immunized with PA-FIS either s.c. (s.c.×2) or i.n. (i.n.×2 or i.n.×3). Three weeks after the booster injection, BAL was performed on at least two animals from each experimental group. The titers of anti-PA and antispore total IgG were determined in duplicate by ELISA (left y axis). Anti-PA neutralizing antibody titers were determined by the TNA assay (TNA, right y axis) as described in Materials and Methods. The data reported represent means of two independent experiments, except for the i.n.×3 guinea pig group (one experiment involving four animals). Bars represent means ± the standard deviations of the log₂ values of the titers measured. For each antibody, an unpaired Student t test was used to compare titers obtained after either i.n.×3 or i.n.×2 immunization to those after s.c.×2 immunization. A P value of ≤0.05 was considered to indicate a statistically significant difference between the means. According to the P value, the difference was significant (*), very significant (**), or extremely significant (***).