Trypanosoma cruzi immunosuppressive factor decreases the interleukin-2 mRNA level in cultured normal activated human lymphocytes

Antibody profiles induced by Trypanosoma cruzi in chagasic patients with previous or current exposure to mycobacteria

Since the immune response mounted by the host to a particular microorganism might be influenced by the acquired immunological experience due to previous contact with other microorganisms, we performed a cross-sectional study to explore the pattern of Trypanosoma cruzi infection-related antibodies in T. cruzi-seropositive individuals presenting concomitant tuberculosis, or the antecedent of BCG vaccination. Sampled individuals were grouped as follows: patients with Chagas disease, not vaccinated with BCG, who further developed pulmonary tuberculosis; individuals with Chagas disease, BCG-vaccinated; and subjects with Chagas disease, presenting neither BCG scar nor tuberculosis disease. Non-vaccinated individuals or without tuberculosis, presented the highest values of anti-PH (P < 0.001), anti-FRA (P < 0.001), anti-p2β (P = 0.0023) and anti-B13 (P < 0.001) antibodies. The present findings constitute the first demonstration of the potential influence of concomitant tuberculosis on Chagas disease.

A soluble factor from Trypanosoma cruzi inhibits transforming growth factor-ß-induced MAP kinase activation and gene expression in dermal fibroblasts

The protozoan parasite Trypanosoma cruzi, which causes human Chagas' disease, exerts a variety of effects on host extracellular matrix (ECM) including proteolytic degradation of collagens and dampening of ECM gene expression. Exposure of primary human dermal fibroblasts to live infective T. cruzi trypomastigotes or their shed/secreted products results in a rapid down-regulation of the fibrogenic genes collagenIα1, fibronectin and connective tissue growth factor (CTGF/CCN2). Here we demonstrate the ability of a secreted/released T. cruzi factor to antagonize ctgf/ccn2 expression in dermal fibroblasts in response to TGF-ß, lysophosphatidic acid or serum, where agonist-induced phosphorylation of the mitogen-activated protein (MAP) kinases Erk1/2, p38 and JNK was also inhibited. Global analysis of gene expression in dermal fibroblasts identified a discrete subset of TGF-ß-inducible genes involved in cell proliferation, wound repair, and immune regulation that are inhibited by T. cruzi secreted/released factors, where the genes exhibiting the highest sensitivity to T. cruzi are known to be regulated by MAP kinase-activated transcription factors. Consistent with this observation, the Ets-family transcription factor binding site in the proximal promoter region of the ctgf/ccn2 gene (−91 bp to −84 bp) was shown to be required for T. cruzi-mediated down-regulation of ctgf/ccn2 reporter expression. The cumulative data suggest a model in which T. cruzi-derived molecules secreted/released early in the infective process dampen MAP kinase signaling and the activation of transcription factors that regulate expression of fibroblast genes involved in wound repair and tissue remodelling, including ctgf/ccn2. These findings have broader implications for local modulation of ECM synthesis/remodelling by T. cruzi during the early establishment of infection in the mammalian host and highlight the potential for pathogen-derived molecules to be exploited as tools to modulate the fibrogenic response.

Survival strategies of Entamoeba histolytica: Modulation of cell-mediated immune responses

Tissue invasion and disease associated with the protozoan Entamoeba histolytica has long been connected with suppression of host cellular immunity. Dampening of the host's defences may facilitate survival of amoebae in extraintestinal sites and development of the characteristic amoebic abscesses. In recent years, several studies have begun to clarify, at the cellular level, the specific effects E. histolytica has on immune cell accessory and effector cell functions. Here, Darren Campbell and Kris Chadee discuss the parasite's multiple modulatory effects on macrophages and T cells and how this manipulation of immune defences may enable the parasite to remain viable in the host. They suggest the putative amoebic molecules involved and potential modulation by the cytokines: interleukins IL-4 and IL-10 and transforming growth factor-beta.

Ultrastructural distribution of poly (A)+ RNA during Trypanosoma cruzi-cardiomyocyte interaction in vitro: a quantitative analysis of the total mRNA content by in situ hybridization

Ultrastructural in situ hybridization was used to visualize the spatial distribution of poly (A)+ RNA and quantitate its relative amount within different cellular compartments of cardiomyocytes after T. cruzi infection. The amount of poly (A)+ RNA remained about the same up to 24 h post-infection. In contrast, its content was reduced 65% after 72 h of interaction, showing a marked decrease in the cell cytoplasm. This decline in poly (A)+ RNA level in host cell cytoplasm was concomitant with intracellular proliferation of T. cruzi amastigotes. Thus, T. cruzi may affect host cell cytoplasmic mRNA stability, associated with the parasite's intracellular multiplication.

The Trypanosoma cruzi immunosuppressive factor (TIF) targets a lymphocyte activation event subsequent to increased intracellular calcium ion concentration and translocation of protein kinase C but previous to cyclin D2 and cdk4 mRNA accumulation

Many immunosuppressive effects of Trypanosoma cruzi can be reproduced in vitro by a preparation consisting of molecules spontaneously released by this protozoan (termed trypanosomal immunosuppressive factor (TIF)). In this work, we attempted to establish whether TIF-induced inhibition of lymphoproliferation results from preventing lymphocyte activation or impairing a post-activation process. Although [3H]thymidine uptake and expression of CD25 by normal human T lymphocytes stimulated with a phorbol ester were markedly reduced by T. cruzi or TIF, translocation of cytosolic protein kinase C (PKC) to the cell membrane was not affected. Lymphoproliferation induced by ionomycin was also inhibited by T. cruzi or TIF but the typical elevation of intracellular calcium ions [Ca2+]i caused by this calcium ionophore was not altered. The increase in [Ca2+]i induced with anti-CD3 antibody was also unaffected by TIF. TIF did not preclude lymphocytes stimulated with phytohemagglutinin from accumulating normal mRNA levels of NFAT1 (also known as NFATp) and NFATc. NFAT1 and NFATc are components of the NFAT complex that controls transcription of genes coding for several cytokines and whose translocation to the nucleus is dependent upon PKC activation and increased [Ca2+]i. In contrast, the mRNA levels of cyclin D2 and cdk4, which form a holoenzyme complex known to regulate cell progression through the G1 phase, were markedly reduced by TIF. These results indicated that TIF did not inhibit lymphocyte activation leading to early secondary signaling but curtailed a mechanism controlling cell progression through G1 and necessary for reaching S phase.

Heat-killed Bacillus subtilis inhibits T-cell proliferative response to mitogens and recall antigens

Heat-killed vegetative forms of Bacillus subtilis were found to impair considerably the capacity of human T-lymphocytes to secrete interleukin-2 (IL-2) and to proliferate (in terms of [3H]thymidine incorporation) after phytohaemagglutinin (PHA) stimulation. B. subtilis was also found to interfere with T-cell proliferation induced by concanavalin A (Con A) and the recall antigen tetanus toxoid (TT). The suppressive activity was dependent on bacterial concentration, and was not ascribed to mitogen, medium-nutrient absorption or cell killing. Moreover, B. subtilis did not interfere with mitogen-induced IL-2 receptor expression on the T-cell surface. On the other hand, B. subtilis did not interfere with T-cell proliferation induced by phorbol myristate acetate (PMA) and ionomycin stimulation. All data obtained suggest the binding of B. subtilis subcomponents to- or very close to-the T-cell receptor (TCR). Identification and purification of the basic structure(s) or component(s) of B. subtilis with TCR antagonist activity in vitro will help to exploit different aspects of T-cell activity and development, and possibly, will provide a means of specific control or modification of the immune response.

Defective production of interleukin 2 in patients with Chagas' disease. Purified IL-2 augments in vitro response in patients with chagasic cardiomyopathy

The production of interleukin 2 (IL-2) by peripheral blood mononuclear cells, from patients with different clinical forms of Chagas' disease and healthy controls, was evaluated after stimulation with Trypanosoma cruzi antigen, PPD and PHA. PHA induced higher production of IL-2 in infected patients than healthy controls. No differences were found between infected groups. With PPD the trend was similar, the only difference was that asymptomatic infected patients (INF) showed higher levels of IL-2 production than patients with cardiomyopathy (CDM). With T. cruzi antigen, most patients showed little or no IL-2 production at 24 hr, a peak at 48 hr and an abrupt fall at 72 hr. A similar pattern of IL-2 production was observed in INF and CDM. To evaluate the physiologic relevance of the deficit in IL-2 production, we studied the effect of non-mitogenic concentrations of IL-2 in the proliferative response to specific antigens. The addition of IL-2 only enhanced the proliferative response of CDM patients. These observations suggest that patients suffering Chagas' disease, particularly CDM, have a significant reduction in the capacity to produce IL-2. These findings could be of importance in the pathogenesis of Chagas' disease.