FIG. 3.

Protective immunity induced by immunization with plasmid DNA encoding a dominant or subdominant epitope and by simultaneous immunization with the three plasmids. Mice were immunized with p91m, p60 217m, or p60 449m or were simultaneously immunized with these plasmids three times and, 2 weeks later after the last immunization, were challenged with 2 × 10⁴ CFU of L. monocytogenes intravenously. Bacterial titers of spleens were determined 72 h after the challenge infection by plating 10-fold dilutions of tissue homogenates on Trypticase soy agar plates. The results are expressed as the mean ± the SD for six mice. ∗, P < 0.01; ∗∗, P = 0.02.