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. Author manuscript; available in PMC: 2023 Jul 4.
Published in final edited form as: Vaccine. 2022 Nov 12;40(52):7676–7692. doi: 10.1016/j.vaccine.2022.11.002

Fig. 9. Lesion attenuation in immunized animals challenged with different doses.

Fig. 9.

Following immunization, rabbits were challenged intradermally on their backs at 10 sites per rabbit with 105 T. pallidum Nichols strain per site (n = 4) or 103 T. pallidum per site (n = 4). At 48 h, evidence of DTH (erythema and induration) was recorded. Unimmunized rabbits showed no evidence of DTH at 48 h. While immunized rabbits challenged with 105 T. pallidum per site developed DTH at nearly all sites by 48 h, rabbits challenged with 103 T. pallidum per site failed to show evidence of DTH at 48 h. The lesions in immunized rabbits were significantly smaller (Fig. 9b) and had fewer T. pallidum detected by qPCR (Fig. 9c) than in unimmunized rabbits, regardless of the challenge dose. Inset in Fig. 9b shows early lesion volumes in rabbits challenged with 103 T. pallidum per site; immunized rabbits demonstrated DTH (erythema and induration) at Day 10 post challenge following the lower dose challenge. Lesions in immunized rabbits challenged with 105 T. pallidum per site had a lower proportion of lesions ulcerating, compared to unimmunized rabbits. In contrast, high proportions of lesions progressed to ulceration in rabbits challenged with 103 T. pallidum per site, regardless of immunization status (Fig. 9d). Data reflect the proportion of challenge sites ulcerating by the end of the observation period: day 41 for 105 dose, and day 48 for 103 dose. Data are shown as mean +/− SEM (Fig. 9 a, b and d) and mean and 95 % CI (Fig. 9c). An unpaired t test was used to analyze the difference between the immunized and unimmunized groups in panels a, c, and d; two-way ANOVA was used in panel b. P < 0.05 was considered to be a significant difference.