T Lymphocytes from Chagasic Patients Are Activated but Lack Proliferative Capacity and Down-Regulate CD28 and CD3ζ

Abstract

Background

Chronic persistent infections have been associated with T lymphocytes functional impairment. The aim of this study was to compare the activation status, the proliferative potential and the expression of CD28 and CD3ζ chain on T lymphocytes between chronic chagasic patients and uninfected controls.

Methodology/Principal Findings

Forty-two chronic chagasic patients, 28 healthy individuals and 32 non-chagasic cardiomyopathy donors were included. Peripheral blood was marked for CD3, CD4, CD8, HLA-DR, CD28, CD38 and intracellular CD3ζ. Peripheral blood mononuclear cells were stained with carboxyfluorescein diacetate succinimidylester and incubated with T. cruzi lysate or phytohemagglutinin for five days. Cells from 3 healthy controls were incubated with T. cruzi trypomastigotes separated with transwells; and the expression of CD3ζ chain and proliferation index was determined. Heart-infiltrating cells from two chronic chagasic patients were tested for the aforementioned cellular markers. Chagasic patients displayed higher frequencies of CD4+/HLA-DR+/CD38+ (8.1%±6.1) and CD8+/HLA-DR+/CD38+ (19.8±8.9) T cells in comparison with healthy (1.6±1.0; 10.6±8.0) and non-chagasic cardiomyopathy donors (2.9±2.9; 5.8±6.8). Furthermore, the percentage of CD4+ activated T cells was higher in chagasic patients with cardiac involvement. CD8+ T cells proliferation index in chagasic donors (1.7±0.3) was lower when compared with healthy (2.3±0.3) and non-chagasic cardiomyopathy individuals (3.1±1.1). The frequencies of CD4+/CD28+ and CD8+/CD28+ T cells, as well as the CD3ζ ^bright/CD3ζ ^dim% ratios in CD4+ and CD8+ were lower in chagasic patients when compared with both control groups. The CD3ζ ^bright/CD3ζ ^dim% ratio and proliferative indexes for CD4+ and CD8+ T lymphocytes decreased gradually in those cells cultivated with parasites and displayed lower values than those incubated with medium alone. Finally, heart-infiltrating T cells from two T. cruzi infected patients also expressed activation markers and down-regulate CD28 and CD3ζ.

Conclusions

CD8+ T lymphocytes from chagasic donors displayed reduced proliferative capacity, which might be associated with CD3ζ down-regulation and diminished CD28 expression on CD4 T cells.

Author Summary

In Chagas disease, caused by Trypanosoma cruzi, there is an acute onset from which most of the individuals recover if a competent immune response develops. Patients can remain asymptomatic (indeterminate) for many years, but near 30% can develop specific organ damage, mainly the heart. The pathogenesis of chronic Chagas cardiomyopathy is associated with parasite persistence, inadequate immune response and autoimmunity. Here we explored the bulk T cells response of chronic chagasic patients with and without cardiomyopathy, uninfected controls and patients with non-chagasic cardiomyopathy. T cells from chagasic donors expressed higher levels of activation markers, and their co-expression on CD4+ T cells distinguished those donors with or without cardiac damage. Mitogen-induced proliferation is highly impaired in the CD8+ T cells compartment, and interestingly activated CD8+ T cells are negatively correlated with the CD4+/CD28− population. The expression of the CD3ζ chain and CD28 was also diminished in chagasic patients. Furthermore, in vitro studies with blood mononuclear cells from uninfected donors showed that the indirect contact with live parasite decreased expression of CD3ζ chain and altered the T cell mitogen-induced proliferation. These results suggest a global impairment of the peripheral T cells response, which is probably associated with parasite persistence.