OBJECTIVE: Invasive lumbar puncture is the conventional method for diagnosing neurosyphilis (NS). We investigated a non-invasive alternative method to detect serum Treponema pallidum-specific antibodies against highly immunogenic antigens TP0171 (TP15), TP0435 (TP17), and TP0574 (TP47) by using luciferase immunosorbent assay.
METHODS: A total of 816 HIV-negative patients suspected of NS from the Beijing and Guangzhou cohorts were retrospectively selected and tested for serum anti-TP15, TP17, and TP47 IgG antibodies. Two diagnostic prediction models were developed using stepwise logistic regression in the Beijing cohort, and evaluated in the Guangzhou cohort for external validation.
RESULTS: Serum antibodies against TP15, TP17, and TP47 showed moderate capability for NS diagnosis in the Beijing cohort and the corresponding area under the receiver operating characteristic curves (AUCs) were 0.722 [95% confidence interval (CI): 0.680-0.762)], 0.780 (95% CI: 0.741-0.817), and 0.774 (95% CI: 0.734-0.811), respectively. An expanded NS prediction model integrated with anti-TP17 and anti-TP47 antibodies showed better performance than the base NS diagnostic model without anti-TP17 and anti-TP47 antibodies with the AUC of 0.874 (95% CI: 0.841-0.906) vs. 0.845 (95% CI: 0.809-0.881) (p = 0.007) in the development cohort, and 0.934 (95% CI: 0.909-0.960) vs. 0.877 (95% CI: 0.840-0.914) (p < 0.001) in validation cohort, respectively. Decision curve analysis revealed that the net benefit of the expanded model exceeded that of the base model when the threshold probability was between 0.10 and 0.95 in both the development and external validation cohorts.
CONCLUSIONS: Serum antibodies against TP17 and TP47 exhibited promising diagnostic capability for NS and significantly enhanced the predictive accuracy of model for NS diagnosis. Our study highlights the potential of serum treponemal antibody detection as a non-invasive method for NS diagnosis to substitute invasive lumbar puncture in NS diagnosis.

To assess the clinical applicability of a semi-quantitative luciferase immunosorbent assay (LISA) for detecting antibodies against Treponema pallidum antigens TP0171 (TP15), TP0435 (TP17), and TP0574 (TP47) in diagnosing and monitoring syphilis. LISA for detection of anti-TP15, TP17, and TP47 antibodies were developed and evaluated for syphilis diagnosis using 261 serum samples (161 syphilis, 100 non-syphilis). Ninety serial serum samples from 6 syphilis rabbit models (3 treated, 3 untreated) and 110 paired serum samples from 55 syphilis patients were used to assess treatment effects by utilizing TRUST as a reference. Compared to TPPA, LISA-TP15, LISA-TP17, and LISA-TP47 showed a sensitivity of 91.9%, 96.9%, and 98.8%, specificity of 99%, 99%, and 98%, and AUC of 0.971, 0.992, and 0.995, respectively, in diagnosing syphilis. Strong correlations (rs = 0.89-0.93) with TPPA were observed. In serial serum samples from rabbit models, significant differences in the relative light unit (RLU) were observed between the treatment and control group for LISA-TP17 (days 31-51) and LISA-TP47 (day 41). In paired serum samples from syphilis patients, TRUST titres and the RLU of LISA-TP15, LISA-TP17, and LISA-TP47 decreased post-treatment (P < .001). When TRUST titres decreased by 0, 2, 4, or ≥8-folds, the RLU decreased by 17.53%, 31.34%, 48.62%, and 72.79% for LISA-TP15; 8.84%, 17.00%, 28.37%, and 50.57% for LISA-TP17; 22.25%, 29.79%, 51.75%, and 70.28% for LISA-TP47, respectively. Semi-quantitative LISA performs well for syphilis diagnosis while LISA-TP17 is more effective for monitoring syphilis treatment in rabbit models and clinical patients.

BACKGROUND: The diagnosis of syphilis is most frequently dependent on antibody detection with serological assays. Assays for both treponemal and non-treponemal antibodies are needed to provide a sensitive and specific diagnosis. For decades, a first screening has been done with non-treponemal assays, followed by treponemal. However, in recent years, following laboratory automation, the reverse sequence screening algorithms have been developed, using a treponemal assay as the initial screening test.
OBJECTIVE: To evaluate serological assays for treponemal and non-treponemal antibodies, to use in reverse algorithm screening of syphilis.
METHODS: Six treponemal assays (one IgM-specific assay), two non-treponemal assays and one novel dual point-of-care (POC) assay for serological diagnosis of syphilis were evaluated. Serum samples from Guinea-Bissau and Sweden were examined, as well as two performance panels and samples from blood donors. Sensitivity and specificity were calculated for each assay, using different assays as gold standard test.
RESULTS: The Macro-Vue RPR Card test was the most sensitive non-treponemal test and the TrepSure Anti-Treponema EIA Screen and the SeroDia TP-PA were the most sensitive and specific treponemal assays. Among the automated assays, both the Liaison Treponema Screen and Architect Syphilis TP showed high sensitivity, however, the former had clearly higher specificity.
CONCLUSIONS: In resourced settings, where the reverse sequence algorithm is preferred for screening, an automated treponemal immunoassay for initial screening subsequently followed by the TrepSure test or TP-PA assay as a second treponemal assay appear highly effective. Finally, a quantitative highly sensitive non-treponemal assay, e.g. the Macro-Vue RPR Card test, could then be used as a supplementary test to evaluate activity of the syphilis infection.