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

Abstract

Specific serologic assays for syphilis cannot differentiate current infections from past infections and are inefficient to monitor efficacy of antibiotic therapy. To develop a new immunologic assay for the identification of active Treponema pallidum infection during the various stages of syphilis. 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). 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. 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.