Reactivity of recombinant Treponema pallidum (r-Tp) antigens with anti-Tp antibodies in human syphilitic sera evaluated by ELISA.

We evaluated the immunoreactivity of recombinant Treponema pallidum (r-Tp) antigens with human sera by indirect enzyme-linked immunoabsorbant assay (ELISA). We expressed antigens with a molecular weight (MW) of 17KDa, 15KDa, 47KDa, and 42KDa, which are believed to be major immunoreactive membrane proteins of Tp cells. The expressed proteins were described by adding the prefix M, S, and G to the corresponding Tp antigens, namely, mature antigens, signal sequence containing antigens, and glutathione s-transferase (GST)-fused antigen in this report. A rather high expression occurred for M47 and S42 proteins in the Escherichia coli system, whereas for M15 and M17 proteins, a poor expression was observed. However, a fairly high expression occurred for G15 and G17. Thus expressed proteins were purified by means of chromatographies to a level of > 95%, and the purified proteins were found to be reactive with TPHA positive serum by Western blotting (WB). An ELISA performed with a serum of 1/1000 dilution using these purified antigens for coating on the solid phase showed that G17 antigen was more effective in detecting syphilis antibodies in human serum than M47, S42, and G15. There was a good consistency between ELISA and TPHA, whereby the cutoff indexes (CI) on ELISA showed a correlation coefficient of 0.7276 in logarithmic TPHA titers.