Enzyme-Linked Immunospot Assay for the Diagnosis of Active Treponema pallidum Infection During the Various Stages of Syphilis

Background: Specific sérologie assays for syphilis cannot differentiate current infections from past infections and are inefficient to monitor efficacy of antibiotic therapy. Goal: To develop a new immunologie assay for the identification of active Treponema pallidum infection during the various stages of syphilis. Study Design: Peripheral blood mononuclear cells obtained from patients with syphilis in an STD clinic were tested for T. pallidum -specific circulating antibody-secreting cells (ASC) by an enzyme-linked immunospot assay (ELISPOT). Results: Specific ASC were demonstrated in all six patients with primary syphilis and in 14 of 16 patients diagnosed with secondary syphilis. ASCs were undetectable in five patients 8 to 16 days after appropriate therapy, but persisted in one case that was considered treatment failure. Among the 13 patients diagnosed with latent syphilis, six (46%) demonstrated ASC, reflecting antigenic stimulation. Conclusion: The ELISPOT assay is effective for the diagnosis of primary and secondary syphilis. The presence of circulating ASC suggests persistent active infection in some patients during the latent disease stage.