FIG. 2.

Antibody responses of mice inoculated with lp25⁺ lp28-1⁺ attenuated and noninfectious pMarGent mutants from two independent multiple-dose experiments. In each experiment, groups of two mice each were inoculated with 1 × 10², 1 × 10⁴, or 1 × 10⁶ spirochetes. Mice were sacrificed after 2 weeks, and serum reactivity was measured using serum from each mouse in a VlsE ELISA. Each symbol represents the mean for triplicate samples from one mouse. Each horizontal bar indicates the mean reactivity for four mice inoculated with a given dose. The dotted line indicates the cutoff value for reactivity (OD₄₀₅ = 0.010), defined as 2 standard deviations above the mean VlsE reactivity for preimmune sera from 32 mice. An asterisk indicates that the reactivity for that inoculum was statistically different from the reactivity observed for the corresponding inoculum of 5A18 NP1 (P < 0.05). The transposon mutants are subdivided into those that were identified as being (A) noninfectious or (B) attenuated in the single mouse inoculation study.