Tp40: a new potential prognostic and diagnostic marker for syphilis

The characterization of Treponema pallidum proteins is of great significance for the study of the prevention, diagnosis, and pathogenesis of syphilis. The structures and functions of many T. pallidum proteins, including the Tp40 (Tp0134) protein, remain unknown. To explore the expression pattern of the Tp40 protein within T. pallidum, we established an animal model of syphilis infection to compare the variations in serum Tp40 antibody levels between Live and Inactivated Tp groups. The results indicated that the absorbance of Tp40-enzyme-linked immunosorbent assay (ELISA) did not increase in the Inactivated group and the Untreated group, but it increased in the Live Tp infection group, suggesting that the Tp40 protein is an in vivo-induced antigen that is only actively expressed during infection. In addition, the localization of the Tp40 protein was determined by the gel microdrop method. We found that Tp40 may be a transmembrane protein with a signaling peptide present in the intima periplasm of T. pallidum. Finally, 468 patients' sera were collected for diagnostic value evaluation. Tp40-ELISA, LZ-ELISA, and Shanghai Kehua rapid plasma reagin (RPR) reagent kit showed a high degree of consistency in 468 serum samples. This suggests that Tp40 could be a valuable diagnostic antigen. The results of this study provide a new reference for the study of the pathogenesis, protein function, and diagnosis of syphilis.

In recent years, syphilis, as a chronic infectious disease, has once again attracted much attention. Treponema pallidum exhibits remarkable infectivity, concealment, and aggressiveness, posing considerable challenges to its prevention and control. The underlying pathogenic mechanisms remain elusive, and during the infection process, the roles of numerous proteins are still unclear. Through protein characterization in this study, it was found that the Tp40 protein is highly likely to be a transmembrane protein with a signal peptide and may be located in the periplasm. Besides, based on experiments with animal models and the detection of human serum samples, we believe that the Tp40 protein is a potential in vivo-induced antigen of T. pallidum that can be used for serological diagnosis of syphilis. This study conducted a preliminary exploration of the Tp40 protein and provided a meaningful reference for further exploration of the functional mechanism of the Tp40 protein and its significance in clinical diagnosis.