A comparison of VDRL and immunoassays developed with a recombinant TmpA antigen in the screening of antibodies to Treponema pallidum

Using the polymerase chain reaction (PCR), and DNA extracted from a lesion of a syphilis patient, we isolated the gene encoding for the mature Treponema pallidum TmpA membrane protein, and expressed this antigen in the cytoplasm of E. coli as a soluble fusion protein. The antigen, purified in one step by immobilized metal ion affinity chromatography (IMAC), was used to develop a visual immunoassay and an ELISA. When these systems were compared with the non-treponemal Venereal Disease Research Laboratories (VDRL) test we found very low discrepancy (0.9% and 0.83%, respectively) in a study of more than 1000 samples. The reactivity pattern of our sera panel in the TmpA visual and ELISA tests indicated that anti-TmpA antibodies are elicited and/or disappear concomitantly with anticardiolipin antibodies. Finally, we obtained a good correlation between the TmpA assays and the Treponema pallidum Haemogglutination Assay (TPHA) in classifying VDRL weakly reactive samples, suggesting their potential use in the confirmation algorithm of syphilis.