Treponema pallidum elicits innate and adaptive cellular immune responses in skin and blood during secondary syphilis: a flow-cytometric analysis

Abstract

Background: Syphilis is caused by the spirochetal pathogen Treponema pallidum. The local and systemic cellular immune responses elicited by the bacterium have not been well studied in humans.

Methods: We used multiparameter flow cytometry to characterize leukocyte immunophenotypes in skin and peripheral blood from 23 patients with secondary syphilis and 5 healthy control subjects recruited in Cali, Colombia. Dermal leukocytes were obtained from fluid aspirated from epidermal suction blisters raised over secondary syphilis skin lesions.

Results: Compared with peripheral blood (PB), blister fluids (BFs) were enriched for CD4(+) and CD8(+) T cells, activated monocytes/macrophages, and CD11c(+) monocytoid and CD11c(-) plasmacytoid dendritic cells (mDCs and pDCs, respectively). Nearly all mDCs in BFs expressed the human immunodeficiency virus (HIV) coreceptors CCR5 and DC-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) and high levels of human leukocyte antigen (HLA)-DR. Dermal pDCs expressed both HIV coreceptors without increases in HLA-DR intensity. Compared with normal blood, circulating mDCs in patients with syphilis expressed higher levels of both CCR5 and DC-SIGN, whereas circulating pDCs in patients expressed only higher levels of DC-SIGN. Most dermal T cells were CCR5(+) and displayed a memory (CD27(+)/CD45RO(+)) or memory/effector (CD27(-)/CD45RO(+)) immunophenotype. A corresponding shift toward memory and memory/effector immunophenotype was clearly discernible among circulating CD4(+) T cells. Compared with PB from control subjects, a larger percentage of CD4(+) T cells in PB from patients with syphilis expressed the activation markers CD69 and CD38.

Conclusions: During secondary syphilis, T. pallidum simultaneously elicits local and systemic innate and adaptive immune responses that may set the stage for the bidirectional transmission of HIV.

Figure 1

Mononuclear cell populations in blister fluid (BF) and peripheral blood (PB) obtained from patients with secondary syphilis. Circulating and dermal T cells, B cells, and monocytes (Mono) were identified on the basis of CD14, CD20, CD45, and CD38 surface expression; dendritic cells (DCs) were identified as being lineage mixture negative and HLA-DR⁺. List mode multiparameter files (consisting of forward and orthogonal scatter and 3 or 4 fluorescence parameters) were analyzed using PAINT-A-GATE^PRO (version 3.0) software (BD Immunocytometry Systems). Median percentage, interquartile range, and both minimum and maximum values are shown for each cell population studied. The Wilcoxon signed-ranks paired test was used to determine statistical differences between median percentage values in BF and PB. P values are shown for each paired comparison.

Figure 2

Expression of dendritic cell (DC)–specific intercellular adhesion molecule 3–grabbing nonintegrin (DC-SIGN) (A) and CCR5 (B) on the surface of CD11c⁺ (monocytoid) and CD11c⁻ (plasmacytoid) DCs obtained from secondary syphilis dermal lesions (BF) and peripheral blood (PB-syph), compared with those obtained from blood from healthy control subjects (NL). DCs were first identified as lineage mixture negative and HLA-DR⁺. Median percentage, interquartile range, and both minimum and maximum values are shown for each cell population studied. The Wilcoxon signed-ranks paired test was used to compare the median percentage of cells expressing each cell surface receptor expression between patients with secondary syphilis' PB and blister fluid. Likewise, the Mann-Whitney U test was used to compare PB from patients with syphilis with that obtained from 5 healthy Colombian volunteers. *P < .05, patient's skin vs. blood. **P < .05, patients' blood vs. blood from healthy control subjects. C, Representative flow-cytometric dot plot for DC CCR5 and DC-SIGN vs. CD11c surface expression on cells obtained from a normal volunteer's PB, and skin and PB from 1 patient with secondary syphilis.