Seroreactivity and immunogenicity of Tp0965, a hypothetical membrane protein of Treponema pallidum

Treponema pallidum (T. pallidum) subsp. pallidum is the causative agent of syphilis. Analysis of recombinant antigens of T. pallidum led to the identification of potential candidate antigens for vaccine development and syphilis serodiagnosis. Tp0965 was predicted to be a membrane fusion protein and was found to be reactive with infected human sera in previous studies, but the results were controversial. In this research, the antigenicity and immunoreactivity of recombinant protein Tp0965 were assessed.

T. pallidum subsp. pallidum (Nichols strain) was propagated and isolated and the genomic DNA was extracted. The Tp0965 gene was amplified by polymerase chain reaction (PCR). Then the recombinant protein Tp0965 was expressed in Escherichia coli and purified by nickel-nitrilotriacetic acid (Ni-NTA) purification system. The reactivities of protein Tp0965 were examined by immunoblot analysis and indirect enzyme-linked immunosorbent assay. The antisera against protein Tp0965 were obtained by immune rabbits and the immunogenicity of antisera were detected by indirect enzyme-linked immunosorbent assay.

Recombinant protein Tp0965 was expressed successfully in vitro. Immunoblot assay showed that the recombinant protein Tp0965 could be recognized by human syphilitic sera of all stages. Indirect enzyme-linked immunosorbent assay showed there were only 4 of 74 human syphilitic sera that failed to show reactivity to recombinant antigen Tp0965, and lack of reactivity of Tp0965 to all 28 uninfected sera. A low titer of antiserum against Tp0965 in immune rabbits could be detected after the third time of immunization.

The recombinant antigen Tp0965 shows excellent sensitivity for the reactivity with sera from syphilitic individuals at all stages. The results also demonstrate a potential application for the serodiagnosis of syphilis.