Effect Of Anti-TP0136 Antibodies On The Progression Of Syphilis Based On An Infected Rabbit Model

Background:Syphilis,which is caused by the spirochete Treponema pallidum subspecies pallidum(T.pallidum),is a sexually transmitted infection.TP0136(a predicted lipoprotein)is one of the few proteins produced by T.pallidum and its allelic variability could have evolved as a method of generating surface antigen diversity among T.pallidum strains as a general mechanism to facilitate immune evasion while maintaining the basic function of adherence to host cells.The anti-TP0136 antibody response to TP0136 is more extensive in the early stages of experimental infection,suggesting that anti-TP0136 antibodies may play an important role in the process of T.pallidum infection.The effect of anti-TP0136 antibodies on the progression of syphilis is poorly understood.This study aimed to investigate the effect of anti-TP0136 antibodies on the progression of lesions in an infected rabbit model.Methods:The role of anti-TP0136 antibody in syphilis infection was evaluated by the challenge experiment after immunization with rTP0136 in New Zealand rabbits.Among them,the animals in the immunized group were immunized with rTP0136 subcutaneously at multiple points.Then,the antibody titer was measured every week after each immunization.When the antibody titer reached 1:50,000,all the rabbits were then challenged with 105 T.pallidum per site along their back.The animals were observed daily for lesion appearance and development;Besides,the blood samples were drawn regularly for serological analysis,and the injection sites were biopsied for analyzing the average local treponemal burden(including tp0574 mRNA and DNA),the expression of cytokines and histological every week until the wound healed.Then,all rabbits were euthanized,and the popliteal lymph nodes were removed,extracted in saline and injected into the testes of randomly assigned rabbits to observe infectivity to evaluate the protective effect of anti-TP0136 antibodies.The rabbits in the control group were injected with normal saline instead of rTP0136.Results:After inoculation with spirochetes,there was no significant difference in serological changes(P>0.05),the time of lesion appearance(8.7±1.5 d vs.8.5±0.6 d,P>0.05),the size of lesion diameter(P>0.05),the proportion of skin lesions(100%vs.95%,P>0.05)or the proportion of ulcerative lesions(92.5%vs.90%,P>0.05)between the two groups(the immunized group and control group).Cutaneous lesion biopsy specimens were obtained from each immunized or control animal at different point in time after challenge.The H&E staining results showed that the immunized animals had markedly higher levels of total cellular infiltrates in the lesions than control animals,indicating a stronger inflammatory response.Although the DNA level of tp0574 in the two groups had no significant difference(P>0.05),the tp0574 mRNA expression level in the immunized group was significantly higher than that in the control group(P<0.05);At the same time,reverse transcription quantitative PCR was used to measure the expression level of cytokine((IL-10,IFN-γ,IL-2,IL-4 and TNFα)in skin lesions at the site of infection.The expression level of IL-10 in the immunized group was significantly higher than that in the control group at 30 d postchallenge(P<0.05).The expression levels of IFN-γ and IL-2 in the immunized group seemed to be higher than those in the control group,but the differences were not significant(P>0.05).The expression levels of IL-4 and TNF-α were not detected after repeated experiments for three times.Interestingly,the lesions in the immunized group took longer to heal than those in the control group(42 d vs.28 d,P<0.001);The rabbit infectivity test had showed that all recipient animals exhibited evidence of seroconversion,and dark-field analysis of the testes of all recipient animals at the time of euthanasia confirmed the presence of motile T.pallidum.Conclusions:Our study showed that high titers of anti-TP0136 antibodies promoted the infiltration of inflammatory cells into local lesions and intensified tissue damage,thus delaying wound healing,and had no protective effect on the occurrence of syphilis in the rabbit model.Explore the role of anti-TP0136 antibody in depth in syphilis infection will help us to further reveal the pathogenesis of syphilis.