Alterations in T lymphocytes and T-lymphocyte subpopulations in patients with syphilis

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

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.

Flow cytometric analysis of peripheral blood lymphocyte immunophenotypes in persons infected with Treponema pallidum

To characterize the human immune response to syphilis, we determined the effect of infection with Treponema pallidum on the percentage of the various lymphocyte subpopulations in the peripheral blood of infected and uninfected persons. Monoclonal antibodies labeled with either fluorescein isothiocyanate or phycoerythrin were used to perform dual color analysis on a FACScan with the following markers: CD3 for total T cells, CD4 for T helper cells, CD8 for T suppressor cells, CD19 for B cells, and CD16 plus CD56 for natural killer cells. Lymphocyte immunophenotype results were analyzed by the stage of untreated syphilis and by gender. Although they were within the ranges of the normal distribution of immunophenotypes, the percentages of CD4+ cells were significantly lower (P < 0.001) and those of CD8+ cells were higher (P = 0.03) in patients with syphilis than in the uninfected population. For infected versus uninfected subjects, both women and men, the differences in the mean percentages of CD3+ and CD4+ cells were significant (P < or = 0.05). Significant differences were noted between the sexes in secondary syphilis only in the mean percentages of cells positive for CD3, CD4, CD8, and CD16 plus CD56. Gender had no effect on lymphocyte subpopulations in subjects with primary or latent syphilis. In the control population, significant differences due to gender were observed in the percentages of cells positive for CD3, CD4, and CD16 plus CD56.

Immune studies in infants with congenital syphilis

Seventeen neonates with congenital syphilis were studied to determine the immune response of the fetus following intra-uterine infection with Treponema pallidum. The results were compared with those from healthy controls matched for gestational age, birth weight and sex. B cells, IgM, and circulating immune complexes were significantly elevated in the infected newborns. There were no differences in lymphocyte transformation to phytohaemagglutinin (PHA) and in the CD3, CD4, and CD8 lymphocytes between infants with congenital syphilis and controls. Newborns with congenital syphilis have a heightened humoral response but no quantitative abnormality in cell-mediated immunity. Speculation on the role of the circulating immune complexes is presented.

Infiltrate of syphilitic lesions before and after treatment

An immunohistological study of skin biopsy specimens from patients with early syphilis was undertaken before and after treatment (one day after intramuscular administration of 2.4 MIU benzathine penicillin and eight days later, after a total administration of 3.6 MIU. In chancres from seronegative patients treatment with 3.6 MIU usually resulted in fewer immunocompetent cells in the infiltrate. In lesions of secondary syphilis treatment with 2.4 MIU benzathine penicillin produced a significant decrease in immunocompetent cells. After treatment with 3.6 MIU there was no further decrease. It was worth noticing that even eight to nine days after the initial pretreatment biopsy, when 3.6 MIU had been administered, the overall lymphohistiocytic infiltrate was not substantially diminished. Significantly more suppressor (T8+) cells were found in lesions of primary syphilis than of secondary syphilis, and they showed remarkable exocytosis. Activated local T8+ cells may release immunosuppressive lymphokines.

Fluctuations in natural killer cell activity in early syphilis

The natural killer cell activity was studied in 25 patients with primary, secondary, or latent syphilis before and after treatment. In primary syphilis natural killer cell activity was increased, especially in patients lacking circulating lipoidal antibodies. In patients who had become seroreactive in the lipoidal tests it was depressed in those with secondary and latent syphilis. The natural killer cell activity thus becomes activated by the syphilitic infection but is significantly reduced during progression of the disease. The importance of the natural killer cell activity in controlling syphilitic infection is questionable.

The immunological profile of mycosis fungoides

The immune reactivity of 25 patients with mycosis fungoides was studied twice with a 6 month interval using a panel of T lymphocyte surface markers and functional tests. Patients with clinically inactive disease (stage I + II) had normal T lymphocyte biology. Patients with clinically active disease (stage II-IV) had T lymphopenia, alterations in T cell subpopulations (T gamma and T mu) and a reduced lymphocyte reactivity in vitro following mitogen (PHA, Con A, PWM) and antigen (PPD) stimulation. They also had a reduced secretion of immunoglobulin in vitro after PWM stimulation, apparently due to the alterations in their T lymphocyte subpopulations. The observed changes in the peripheral blood T lymphocyte population and the in vitro function of lymphocytes were not shared by lymphocytes from histologically affected lymph nodes. The natural killer cell activity in blood lymphocytes was found to be normal in all patients.

Depression of natural killer cell activity by syphilitic serum and immune complexes

Consecutive serum samples were obtained from patients with syphilis before and on three occasions after treatment. The sera contained immunosuppresive factors associated with the immunoglobulin fraction, which could depress the natural killer cell activity of healthy controls. There was no evidence that allogeneic or lymphocytotoxic antibodies played a role in immuno-suppression, which could be reproduced with both soluble and insoluble antigen-IgG-antibody complexes.