Performance of novel infection phase-dependent antigens in syphilis serodiagnosis and treatment efficacy determination

Liu, W; Deng, MX; Zhang, XH; Yin, WG; Zhao, T; Zeng, TB; Liu, SQ; Xiao, YJ; Zhang, L; Luo, X; Zhao, FJ

Zhao, FJ (reprint author), Univ South China, Inst Pathogen Biol, Hunan Prov Key Lab Special Pathogens Prevent & Co, 28 Changsheng West Rd, Hengyang 421001, Hunan, Peoples R China.

CLINICA CHIMICA ACTA, 2019; 488 (): 13

Abstract

Objective: The objective of this study was to screen new antigens for syphilis serodiagnosis. Methods: First, we determined whether the Treponema pallidum proteins Tp0971, Tp0768 and Tp0462 were infection phase-dependent antigens by observing serum reactivity differences in New Zealand rabbits infected with activated or inactivated T. pallidum. A non-infection phase-dependent antigen, the Tp92 membrane protein, was used as the negative control. Next, Tp0971-, Tp0768- and Tp0462-based ELISA was performed on 2138 human serum samples and compared with the T. pallidum passive particle agglutination assay (TPPA) and LiZhu (TM) Tp-ELISA. In addition, another 60 paired serum samples from patients at follow-up were analysed to evaluate the relationships between titre changes and differences in the A450 nm values of the Tp0971, Tp0768, Tp0462 and Tp92 antibodies measured by ELISA. Results: Compared with Tp92 (negative control), Tp0971, Tp0768 and Tp0462 were determined to be infection phase-dependent antigens. Compared with those of the TPPA, the sensitivities of Tp0971-, Tp0768- and Tp0462-based ELISA were 96.4%, 96.9% and 93.0%, respectively, and the specificities were 97.7%, 95.4% and 98.9%, respectively, resulting in consistencies of 97.1%, 96.2% and 95.9%, respectively. Compared with those of the LiZhu (TM) Tp-ELISA, the consistencies of Tp0971-, Tp0768- and Tp0462-based ELISA were 95.1%, 94.2% and 94.0%, respectively, with kappa values of 0.902, 0.884 and 0.880, respectively. Tp0971, Tp0768 and Tp0462 demonstrated high sensitivities and specificities, as well as high conformity to the TPPA and LiZhu (TM) Tp-ELISA. Moreover, a significantly positive Spearman rank correlation coefficient (0.82,*P < 0.05) was found between the difference in the A450 nm values of the Tp0971 antibody and the RPR titre change. Conclusion: The infection phase-dependent antigens Tp0971, Tp0768 and Tp0462 are promising for syphilis diagnosis, and Tp0971 may be utilized to monitor curative effects during syphilis treatment.

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