Enzyme-linked immunospot assay for the diagnosis of active treponema pallidum infection during the various stages of syphilis

Background: Specific serologic assays for syphilis cannot differentiate cur rent infections from past infections and are inefficient to monitor efficac y of antibiotic therapy. Goal: To develop a new immunologic assay for the identification of active T reponema pallidum infection during the various stages of syphilis. Study Design: Peripheral blood mononuclear cells obtained from patients wit h syphilis in an STD clinic were tested for T. pallidum-specific circulatin g antibody-secreting cells (ASC) by an enzyme-linked immunospot assay (ELIS POT). Results: Specific ASC were demonstrated in all six patients with primary sy philis and in 14 of 16 patients diagnosed with secondary syphilis. ASCs wer e 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, reflec ting antigenic stimulation. Conclusion: The ELISPOT assay is effective for the diagnosis of primary and secondary syphilis. The presence of circulating ASC suggests persistent ac tive infection in some patients during the latent disease stage.