Expression of Tp0319 recombinant protein from Treponema pallidum and analysis of its immunocompetence.

Objective To clone, express Tp0319 gene from Treponemapallidum (T. pallidum), and to assess the immunocompetence of recombinant protein. Methods The immuno-dominant region of Tp0319gene was chosen by computer analysis, amplified from T. pallidum complete genome by PCR, subcloned into the expression vector pQE32 to construct a recombinant plasmid, pQE32/Tp0319, which was then expressed in E. coli M15. The recombinant protein was purified with Ni-NTA affinity chromatography, and identified by using sodium dodecyl sulfate polyacrylamide gel electropheresis (SDS-PAGE) and Western blot. New Zealand rabbits were immunized with the recombinant protein, and the titer of anti-Tp0319 antibodies in sera from immunized rabbits were measured with indirect ELISA. Also, indirect ELISA with the recombinant Tp0319 as coating antigen was performed to detect the anti-Tp0319 antibody in sera from 200 normal human controls and 200 patients with syphilis. Results The prokaryotic expression vector pQE32/Tp0319 was constructed successfully, and the recombinant protein Tp0319 with a molecular weight of about 30 000 was attained. Specific humoral response was elicited by the recombinant protein in New Zealand rabbits and the specific antibody titer was more than 1: 10 240 after immunization for 3 times. Western blot proved that the recombinant protein could specifically react with anti-T. pallidum IgG antibody-positive sera. Indirect ELISA was successfully developed with the recombinant Tp0319, and detected antibodies to T. pallidum in control sera with a sensitivity and specificity of 100% (40/40), respectively. Compared with T. pallidum particle agglutination (TPPA) assay, the sensitivity and specificity of the indirect ELISA were 92.6% and 100%, respectively, in the detection of T. pallidum in sera from patients and controls, and the concordance between the indirect ELISA and TPPA was 96%. Conclusions The prepared recombinant protein shows a satisfactory immunocompetence, which may lay a foundation for its further application in the serodiagnosis of syphilis. Key words: Treponema pallidum;  Recombinant proteins;  Immunocompetence