Assessment of recombinant antigens Tp0100 and Tp1016 of Treponema pallidum for serological diagnosis of syphilis

Objective To discover novel serodiagnostic candidates for the serological diagnosis of syphilis. Methods Two recombinant Treponema pallidum proteins Tp0100 and Tp1016 were expressed, purified, and identified by Western Blotting. A total of 600 clinical serum samples were tested with the Tp0100-based ELISA, the Tp1016-based ELISA, and the commercial LICA Syphilis TP kit (ChIVD, Beijing, China). The sensitivities were determined by testing 340 samples from individuals with clinically diagnosed primary, secondary, latent, and tertiary syphilis. The specificities were determined by screening 260 samples from healthy controls and individuals with potentially cross-reactive infections, including leptospirosis, Lyme disease, hepatitis B, tuberculosis, rheumatoid arthritis, systemic lupus erythematosus. Kappa (kappa) values were applied to compare the agreement between clinical syphilis diagnosis and the Tp0100-based ELISA, the Tp1016-based ELISA, or the LICA Syphilis TP test. Results Using clinical syphilis diagnosis as the gold standard, Tp0100 exhibited an overall sensitivity of 95.6% and specificity of 98.1% for testing IgG antibody while Tp1016 demonstrated only an overall sensitivity of 75.0% and specificity of 79.6%. In contrast, the LICA Syphilis TP test revealed an overall sensitivity of 97.6% and specificity of 96.2%. In addition, the overall percent agreement and corresponding kappa values were 96.7% (95% CI 95.6%-97.8%) and 0.93 for the Tp0100-based ELISA, 77.0% (95% CI 74.3%-79.7%) and 0.54 for the Tp1016-based ELISA, and 97.0% (95% CI 96.0%-98.0%) and 0.94 for the LICA Syphilis TP test, respectively. Conclusion The recombinant T. pallidum protein Tp0100 shows promise as a novel diagnostic antigen in the serological tests for syphilis.