Fig. 10. Heterologous protection of the tri-antigen cocktail (UW).

a. Immunization with the tri-antigen cocktail resulted in decreased lesion volume in rabbits challenged with the heterologous strains T. pallidum subsp. pallidum Chicago (Fig. 10a, left panel) and T. pallidum subsp. pallidum Sea 81–4 (Fig. 10a, right panel). Means +/− SEM are shown. Differences between immunized and unimmunized animals in each group were analyzed by an unpaired t test with Welch’s correction at each time point. P < 0.05 was considered to be significant and is shown by *. b. Number of copies of tp0574 (single copy gene) in pooled (by rabbit) lesion aspirates for unimmunized and immunized rabbits challenged with T. pallidum subsp. pallidum Chicago (Fig. 10b, left panel) and pooled (by rabbit) biopsies for animal groups challenged with T. pallidum subsp. pallidum Sea 81–4 (Fig. 10b, right panel). Lesion aspirates were taken on day 22 (Chicago) and biopsies were collected on day 25 (Sea 81–4) post-challenge; timing of the sampling was determined by the appearance of the lesions (large but not yet ulcerating) in the unimmunized animals for each strain c. Time (days) to orchitis or qPCR quantitation for the RIT rabbits receiving LN from the unimmunized control and tri-antigen-immunized rabbit groups challenged with T. pallidum subsp. pallidum Chicago (Fig. 10c, left panel) or T. pallidum subsp. pallidum Sea 81–4 (Fig. 10c, right panel). Animals receiving LN from immunized rabbits exhibited a slight trend towards delayed orchitis, although statistical significance was not achieved. For the Sea 81–4 challenged rabbits, because the Sea 81–4 strain produces virtually no lesions or orchitis following infection, time to development of orchitis in recipient animals could not be determined, nor could lesion aspirates be collected to assess T. pallidum burden. Instead dissemination in the Sea 81–4 RIT recipient animals was determined by extracting the testes from RIT recipient rabbits into a defined volume of saline, followed by qPCR to determine the relative amount of T. pallidum dissemination in the challenged rabbits. There was a significant difference between the immunized and unimmunized groups, although the absolute tp0574 copies were very low. Data shown are mean and 95 % CI and differences between immunized and unimmunized animals in each group were analyzed by the Mann-Whitney test. P < 0.05 was considered significant.