FIG 2.

IgG response to oral immunization with E. coli expressing LigA7-13. Hamsters were immunized orally with E. coli expressing LigA7-13 (LigA7-13-immunized group) or with E. coli containing the empty vector (control-immunized group). The immunization protocol included an initial immunization of 2 weeks (shaded), followed by 1 week of rest, a third week of immunization for the first boost (shaded), 1 week of rest, and a fourth week of immunization for the second boost (shaded). Serum samples were collected at different time points during oral immunization with total doses of either 37 mg in experiment 1 (A) or 148 mg in experiment 2 (B) of LigA7-13. Hamsters were challenged the week following the last week of immunization using either the i.p. route (experiment 1) or i.d. route (experiment 2) of inoculation. LigA7-13 antibody levels were measured in triplicate by ELISA. Geometric mean endpoint and standard deviation are shown for each animal in both experiments (one color per animal). The dotted line shows the critical limit, defined as the value of the mean level of the control-immunized group plus 1.65 SD (experiment 1 = 0.236; experiment 2 = 0.427). Asterisks indicate animals that survived challenge.