Immunoregulatory mechanisms in Chagas disease: modulation of apoptosis in T-cell mediated immune responses.

BACKGROUND: Chronic Chagas disease presents different clinical manifestations ranging from asymptomatic (namely indeterminate) to severe cardiac and/or digestive. Previous results have shown that the immune response plays an important role, although no all mechanisms are understood. Immunoregulatory mechanisms such as apoptosis are important for the control of Chagas disease, possibly affecting the morbidity in chronic clinical forms. Apoptosis has been suggested to be an important mechanism of cellular response during T. cruzi infection. We aimed to further understand the putative role of apoptosis in Chagas disease and its relation to the clinical forms of the disease. METHODS: Apoptosis of lymphocytes, under antigenic stimuli (soluble T. cruzi antigens - TcAg) where compared to that of non-stimulated cells. Apoptosis was evaluated using the expression of annexin and caspase 3(+) by T cells and the percentage of cells positive evaluated by flow cytometry. In addition activation and T cell markers were used for the identification of TCD4(+) and TCD8(+) subpopulations. The presence of intracellular and plasma cytokines were also evaluated. Analysis of the activation status of the peripheral blood cells showed that patients with Chagas disease presented higher levels of activation determined by the expression of activation markers, after TcAg stimulation. PCR array were used to evaluate the contribution of this mechanism in specific cell populations from patients with different clinical forms of human Chagas disease. RESULTS: Our results showed a reduced proliferative response associated a high expression of T CD4(+)CD62L(-) cells in CARD patients when compared with IND group and NI individuals. We also observed that both groups of patients presented a significant increase of CD4(+) and CD8(+) T cell subsets in undergoing apoptosis after in vitro stimulation with T. cruzi antigens. In CARD patients, both CD4(+) and CD8(+) T cells expressing TNF-α were highly susceptible to undergo apoptosis after in vitro stimulation. Interestingly, the in vitro TcAg stimulation increased considerably the expression of cell death TNF/TNFR superfamily and Caspase family receptors genes in CARD patients. CONCLUSIONS: Taken together, our results suggest that apoptosis may be an important mechanism for the control of morbidity in T. cruzi infection by modulating the expression of apoptosis genes, the cytokine environment and/or killing of effector cells.

Inflammatory mediators from monocytes down-regulate cellular proliferation and enhance cytokines production in patients with polar clinical forms of Chagas disease.

Exposure to Trypanosoma cruzi parasites induces monocytes and macrophages to produce various endogenous mediators, including prostaglandins and cytokines. To clarify the involvement of monocytes as an important source of inflammatory mediators in Chagas disease patients, we evaluated PBMC before and after depletion of adherent cells (monocytes) from patients with indeterminate (IND) and cardiac (CARD) clinical forms and from non-infected individuals (NI). We demonstrated that after the partial depletion of adherent cells, production of PGE2 was slightly decreased in patients with Chagas disease. Inhibition of the cells by indomethacin increased the proliferation in PBMC cells from patients after antigen stimulation. Pro-inflammatory cytokines as IL-2 and IFN-γ also had a greater decrease after partial depletion of adherent cells in both clinical forms of Chagas disease. IL-10 and IL-5 levels were also reduced after partial depletion of adherent cells both in IND and CARD patients. In addition, we evaluated the APC potential of B cells and observed that the MHCII and CD80 molecules had an increased expression after partial depletion of most monocytes in all groups. Thus, inflammatory mediators produced by monocytes seem to be important to modulate immune responses in Chagas disease by regulating the processes of inflammation and antigen presentation.

Potential role of CD4+CD25HIGH regulatory T cells in morbidity in Chagas disease.

Several immunoregulatory mechanisms are proposed to be effective both in human and experimental Trypanosoma cruzi infection. However, the role of CD4+CD25high T cells in Chagas disease has not yet been elucidated. These cells are critical for the regulation of immune response to infectious agents and in the control of autoimmune diseases. In this study, the presence of CD4+CD25high regulatory T cells in the whole blood of non-infected individuals (NI), and patients with the indeterminate (IND) and cardiac form (CARD) of Chagas disease was evaluated. To further characterize this population of regulatory cells, the co-expression of CTLA-4, CD62L, CD45RO, CD45RA, HLA-DR, CD40L, CD69, CD54, IL-10R and the intracellular molecules FOXP3 and IL-10 on the CD4+CD25high T lymphocytes was examined. FOXP3 was expressed by the majority of CD4+CD25high when compared with the other CD4+ T cells subsets in patients with Chagas disease. Patients with the IND form of the disease had a higher frequency of circulating regulatory CD4+CD25high T cells than patients with the CARD form. Moreover, there was an increase in CD4+CD25highFOXP3+ cells that were also IL-10+ in the IND group whereas, in the CARD group, there was an increase in the percentage of CD4+CD25high FOXP3+ cells that expressed CTLA-4. These data suggest that IL-10 produced by regulatory T cells is effective in controlling disease development in patients with the IND form. However, in individuals with the CARD form of the disease, the same regulatory mechanism, mediated by IL-10 and CTLA-4 expression is not sufficient to control the progression of the disease. The data suggest that CD4+CD25highFOXP3+ regulatory T cells in patients with Chagas disease might play a role in the immune response against T. cruzi infection although with distinct effects in patients with the IND and CARD forms of disease.

Human immune response to triatomine embryo extract

Dipetalogaster maximus embryo extracts were used to stimulate peripheral blood mononuclear cells (PBMC) and in ELISA with sera either from Trypanosoma cruzi infected or non-infected individuals. The results showed that there was significant proliferative response and high antibody, titers in sera of chagasic patients.