Syphilis, caused by Treponema pallidum, remains a major global health burden. Given the key role of T cell–mediated immunity in T. pallidum clearance, this study evaluates a Tp0136-derived T-cell epitope (Tp0136^T1) delivered via two platforms: lipid nanoparticle–encapsulated nucleoside-modified mRNA (LNP-mRNA) and Pyrococcus furiosus thioredoxin (PfTrx). In BALB/c mice, both platforms elicited robust Th1-type responses, with increased IL-2 and IFN-γ secretion and activation of Th1 CD4⁺ T cell. Only LNP-mRNA-Tp0136^T1 induced strong CD8⁺ cytotoxic responses, marked by elevated perforin⁺ and granzyme B⁺ expression. In New Zealand White rabbits challenged intradermally with T. pallidum, complete ulcer prevention was achieved with the PfTrx-Tp0136^T1, while LNP-mRNA-Tp0136^T1 significantly reduced ulceration. Both vaccines suppressed RPR titers and lowered treponemal load. These findings demonstrate that epitope-specific T cell–based vaccines elicit potent cellular immunity, control treponemes, prevent ulcers, and may reduce secondary sexually transmitted infections by preserving mucosal integrity.

Objective: The immunological mechanisms underlying the syphilis serofast remain incompletely elucidated. This systematic review and meta-analysis aims to quantify the association between key immune indicators and serofast. Methods: We systematically searched PubMed, Embase, Web of Science, Google Scholar and Chinese databases (CNKI, VIP, and CBMdisc) until December 31, 2024, for case-control, cross-sectional or cohort studies meeting serofast criteria (RPR/TRUST titer ≤1:8 persisting for ≥12 months). Random-effects models were used to calculate standardized mean differences (SMD) with 95% confidence intervals (CIs). The risk of bias was assessed using the Newcastle-Ottawa Scale (for observational studies) by two independent reviewers. Results: A total of 38 studies involving 5082 patients were included. The serofast group exhibited significant immune dysregulation: (1) Cellular immune suppression:decreased CD4+ T cells (SMD=-0.61, I²=33.5%) and increased CD8+ T cells (SMD = 0.40, I²=66.7%), leading to an inverted CD4+/CD8+ ratio (SMD=-0.44, I²=64.7%); (2) Th1/Th2 shift:suppression of Th1 cytokines (e.g., IFN-γ, SMD=-2.19, I²=95.7%) with a predominant Th2 response (e.g., IL-10, SMD =+ 2.63,I²=92.5%); (3) Humoral abnormalities: persistently elevated IgM (SMD = 0.96,I²=94.4%) and complement consumption (C3,SMD=-0.60, I²=89.0%; C4, SMD=-0.80, I²=87.6%); (4) Signaling dysregulation: downregulated TLR2 expression and disordered chemokine receptors (TLR2 mRNA,SMD=-1.52, I²=36.0%).The substantial heterogeneity (I² > 50%) observed in several analyses was explored in subgroup and sensitivity analyses, as detailed in the main text. Conclusions: The serofast is characterized by a cascade of “cellular immune suppression-Th1/Th2 shift-complement exhaustion.” Our findings establish a quantified immunological basis for the serofast state and suggest potential targets for immunomodulatory therapy. Systematic review registration: https://www.crd.york.ac.uk/prospero/ , identifier CRD420251156478.

Our previous research identified a luciferase immunosorbent assay (LISA) for detecting serum antibodies against Tp17 and Tp47 as a potential tool for diagnosing neurosyphilis (NS). In this study, we developed a serological test based on a multi-antigen fusion protein (Tp15-17-47) to simplify the detection process and improve the diagnostic accuracy for NS. The Tp15, Tp17, and Tp47 genes were amplified separately by polymerase chain reaction (PCR) and assembled into a fusion gene coding for a tripartite fusion protein antigen using overlap PCR. This recombinant Tp15-17-47 antigen was used retrospectively to detect serum anti-Tp15-17-47 IgG antibodies in 434 HIV-negative patients suspected of NS from cohorts in Beijing and Guangzhou. Two diagnostic prediction models were developed using stepwise logistic regression. Serum anti-Tp15-17-47 IgG antibodies demonstrated moderate diagnostic capability for NS in the development cohort, with an area under the curve (AUC) of 0.791 (95% CI: 0.735-0.846). An optimized NS prediction model substituting anti-Tp15-17-47 antibodies for TRUST/RPR outperformed the base NS diagnostic model. The optimized model achieved an AUC of 0.877 (95% CI: 0.835-0.919) compared to 0.843 (95% CI: 0.795-0.890) for the base model in the development cohort (p = 0.035). This superior performance was confirmed in the validation cohort (AUC: 0.880, 95% CI: 0.827-0.933 vs. 0.792, 95% CI: 0.726-0.859; p < 0.001). Decision curve analysis (DCA) revealed that the optimized model provided greater net benefit than the base model across threshold probabilities ranging from 0.10 to 0.95 in both cohorts. Quantitative profiling of serum IgG targeting the recombinant treponemal antigen Tp15-17-47, along with its diagnostic model, exhibited robust discriminatory power for neurosyphilis diagnosis, which supports the viability of replacing lumbar puncture with this less invasive serological strategy for neurosyphilis ascertainment.