Abstract:

Wang Qi, Yin Yueping, Gong Kuanglong. Institute of Dermatology, Chinese Academy of Medical Sciences and Peking Union Medical College, Nanjing 210042, China Corresponding author: Yin Yueping, Email: yinyp@ncstdlc.org 【Abstract】 Objective To observe clinical manifestations and immune responses in rabbit models of syphilis established by inoculation with Treponema pallidum through different routes. Methods A total of 20 rabbits were randomly and equally divided into two groups: testis-inoculated group injected with Treponema pallidum （Tp） suspensions into the testes, back-inoculated group intracutaneously injected with Tp suspensions at six sites on the shaved back. All the rabbits received a single injection with the total injection amount of Tp （Nichols strains） being 2 × 107 in both groups. Clinical symptoms and immune responses were evaluated in both groups every other day. Statistical analysis was carried out by a two-sample t-test and rank sum test with the SPSS 20.0 software. Results On day 8 after the inoculation, the testes of rabbits in the testis-inoculated group started to swell with induration, and the swelling was most severe during days 13 - 16. Afterwards, the testes gradually diminished, and returned to normal in size without swelling or hardening on day 28. No skin lesions occurred in the other sites in the testis-inoculated group within 2 months after the inoculation. Erythematous swelling occurred at inoculation sites on day 7 after inoculation in the back-inoculated group, which was most obvious between days 15 and 45. Moreover, cartilage-like indurated ulcers were observed at 12 inoculation sites in 3 rabbits in the back-inoculated group, and dark-field examination of the ulcers showed the presence of Tp. There was a significant difference in the time required for the severity of lesions to peak between the testis-inoculated group and back-inoculated group （14.50 ± 1.08 days vs. 29.00 ± 10.30 days, t = 5.02, P < 0.05）. Rank sum test showed significant differences in the distribution of highest RPR titers between the two groups （P < 0.05）, and RPR titers were higher in the testis-inoculated group than in the back-inoculated group. Conclusions The injection of Tp suspensions at different sites can cause different clinical symptoms and immune responses in rabbits. RPR turned positive earlier with a higher titer in the testis-inoculated group compared with the back-inoculated group. The clinical manifestations in the back-inoculated group were similar to those of chancre in primary syphilis in human.