Treponema pallidum periplasmic and membrane proteins are recognized by circulating and skin CD4+ T cells

BackgroundHistologic and serologic studies suggest the induction of local and systemic Treponema pallidum (Tp)-specific CD4+ T cell responses to Tp infection. We hypothesized that Tp-specific CD4+ T cells are detectable in blood and in the skin rash of secondary syphilis and persist in both compartments after treatment. MethodsPBMC collected from 67 participants were screened by IFN{gamma} ELISPOT response to Tp sonicate. Tp-reactive T cell lines from blood and skin were probed for responses to 88 recombinant Tp antigens. Peptide epitopes and HLA class II restriction were defined for selected antigens. ResultsWe detected CD4+ T cell responses to Tp sonicate ex vivo. Using Tp-reactive T cell lines we observed recognition of 14 discrete proteins, 13 of which localize to bacterial membranes or the periplasmic space. After therapy, Tp-specific T cells persisted for at least 6 months in skin and 10 years in blood. ConclusionsTp infection elicits an antigen-specific CD4+ T cell response in blood and skin. Tp-specific CD4+ T cells persist as memory in both compartments long after curative therapy. The Tp antigenic targets we identified may be high priority vaccine candidates.