Treponema pallidum Periplasmic and Membrane Proteins Are Recognized by Circulating and Skin CD4+ T Cells.

Background Histologic and serologic studies suggest the induction of local and systemic Treponema pallidum -specific CD4⁺ T-cell responses to T. pallidum infection. We hypothesized that T. pallidum -specific CD4⁺ T cells are detectable in blood and in the skin rash of secondary syphilis and persist in both compartments after treatment. Methods Peripheral blood mononuclear cells collected from 67 participants were screened by interferon-γ (IFN-γ) ELISPOT response to T. pallidum sonicate. T. pallidum -reactive T-cell lines from blood and skin were probed for responses to 89 recombinant T. pallidum antigens. Peptide epitopes and HLA class II restriction were defined for selected antigens. Results We detected CD4⁺ T-cell responses to T. pallidum sonicate ex vivo. Using T. pallidum -reactive T-cell lines we observed recognition of 14 discrete proteins, 13 of which localize to bacterial membranes or the periplasmic space. After therapy, T. pallidum -specific T cells persisted for at least 6 months in skin and 10 years in blood. Conclusions T. pallidum infection elicits an antigen-specific CD4⁺ T-cell response in blood and skin. T. pallidum -specific CD4⁺ T cells persist as memory in both compartments long after curative therapy. The T. pallidum antigenic targets we identified may be high-priority vaccine candidates. [ABSTRACT FROM AUTHOR]