Objective: 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.
Method: LISA for detection of anti-TP15, TP17, and TP47 antibodies was developed and evaluated for syphilis diagnosis using 261 serum samples (161 syphilis, 100 non-syphilis). 90 serial serum samples from six syphilis rabbit models (three treated, three untreated) and 110 paired serum samples from 55 syphilis patients were used to assess treatment effects by utilizing TRUST as reference.
Results: Compared to TPPA, LISA-TP15, LISA-TP17, and LISA-TP47 showed 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 difference in the relative light unit (RLU) were observed between the treatment and control group for LISA-TP17 (days 31-51) and LISA-TP47 (days 41). In paired serum samples form syphilis patients, TRUST titers and the RLU of LISA-TP15, LISA-TP17, and LISA-TP47 decreased post treatment (P < 0.001). When TRUST titers 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.
Conclusion: Semi-quantitative LISA performs well for syphilis diagnosis while LISA-TP17 is more effective for monitoring syphilis treatment in rabbit models and clinical patients.
Keywords: Treponema pallidum, treponemal antibodies, TP0171 (TP15), TP0435 (TP17), TP0574 (TP47), luciferase immunosorbent assay, syphilis diagnosis, treatment monitoring.