Pivotal role of interleukin-12 and interferon-gamma axis in controlling tissue parasitism and inflammation in the heart and central nervous system during Trypanosoma cruzi infection

Trypanosoma cruzi-elicited CD8+ T cell-mediated myocarditis: chemokine receptors and adhesion molecules as potential therapeutic targets to control chronic inflammation?

In Chagas disease, during the acute phase, the establishment of inflammatory processes is crucial for Trypanosoma cruzi control in target tissues and for the establishment of host/parasite equilibrium. However, in about 30% of the patients, inflammation becomes progressive, resulting in chronic disease, mainly characterized by myocarditis. Although several hypothesis have been raised to explain the pathogenesis of chagasic myocardiopathy, including the persistence of the parasite and/or participation of autoimmune processes, the molecular mechanisms underlying the establishment of the inflammatory process leading to parasitism control but also contributing to the maintenance of T. cruzi-elicited chronic myocarditis remain unsolved. Trying to shed light on these questions, we have for several years been working with murine models for Chagas disease that reproduce the acute self-resolving meningoencephalitis, the encephalitis resulting of reactivation described in immunodeficient individuals, and several aspects of the acute and chronic myocarditis. In the present review, our results are summarized and discussed under the light of the current literature. Furthermore, rational therapeutic intervention strategies based on integrin-mediated adhesion and chemokine receptor-driven recruitment of leukocytes are proposed to control T. cruzi-elicited unbalanced inflammation.

Low penetrance, broad resistance, and favorable outcome of interleukin 12 receptor beta1 deficiency: medical and immunological implications

The clinical phenotype of interleukin 12 receptor beta1 chain (IL-12Rbeta1) deficiency and the function of human IL-12 in host defense remain largely unknown, due to the small number of patients reported. We now report 41 patients with complete IL-12Rbeta1 deficiency from 17 countries. The only opportunistic infections observed, in 34 patients, were of childhood onset and caused by weakly virulent Salmonella or Mycobacteria (Bacille Calmette-Guérin -BCG- and environmental Mycobacteria). Three patients had clinical tuberculosis, one of whom also had salmonellosis. Unlike salmonellosis, mycobacterial infections did not recur. BCG inoculation and BCG disease were both effective against subsequent environmental mycobacteriosis, but not against salmonellosis. Excluding the probands, seven of the 12 affected siblings have remained free of case-definition opportunistic infection. Finally, only five deaths occurred in childhood, and the remaining 36 patients are alive and well. Thus, a diagnosis of IL-12Rbeta1 deficiency should be considered in children with opportunistic mycobacteriosis or salmonellosis; healthy siblings of probands and selected cases of tuberculosis should also be investigated. The overall prognosis is good due to broad resistance to infection and the low penetrance and favorable outcome of infections. Unexpectedly, human IL-12 is redundant in protective immunity against most microorganisms other than Mycobacteria and Salmonella. Moreover, IL-12 is redundant for primary immunity to Mycobacteria and Salmonella in many individuals and for secondary immunity to Mycobacteria but not to Salmonella in most.

Resistant mice lacking interleukin-12 become susceptible to Trypanosoma cruzi infection but fail to mount a T helper type 2 response

Interleukin-12 (IL-12) is essential to resistance to Trypanosoma cruzi infection because it stimulates the synthesis of interferon-gamma (IFN-gamma) that activates macrophages to a parasiticidal effect. Investigation of mice deprived of IL-12 genes (IL-12 knockout mice) has confirmed the important role of IL-12 and IFN-gamma in controlling parasitism in T. cruzi infection. However, it has not yet been addressed whether a shift towards a T helper type 2 (Th2) pattern of cytokine response occurred in these mice that might have contributed to the aggravation of the infection caused by IL-12 deprivation. We examined the course of T. cruzi (Y strain) infection and the regulation of cytokine responses and nitric oxide production in C57BL/6 IL-12 p40-knockout mice. The mutant mice were extremely susceptible to the infection as evidenced by increased parasitaemia, tissue parasitism and mortality in comparison with the control C57BL/6 mouse strain (wild-type) that is resistant to T. cruzi. A severe depletion of parasite-antigen-specific IFN-gamma response, without an increase in IL-4 or IL-10 production, accompanied by reduced levels of nitric oxide production was observed in IL-12 knockout mice. We found no evidence of a shift towards a Th2-type cytokine response. In IL-12 knockout mice, the residual IFN-gamma production is down-regulated by IL-10 but not by IL-4 and nitric oxide production is stimulated by tumour necrosis factor-alpha. Parasite-specific immunoglobulin G1 antibody levels were similar in IL-12 knockout and wild-type mice, whereas IL-12 knockout mice had much higher levels of immunoglobulin G2b.

Interleukin-4 biases differentiation of B cells from Trypanosoma cruzi-infected mice and restrains their fratricide: role of Fas ligand down-regulation and MHC class II-transactivator up-regulation

In the present work, we demonstrate that interleukin (IL)-4 is able to rescue B cells from Trypanosoma cruzi-infected mice, counteracting the strong apoptotic signals that these cells received in vivo. We have observed that IL-4 restrains the apoptosis of immunoglobulin (Ig)M(+) and IgG(+) B cells from infected and normal mice without inducing them to proliferate. In addition, IL-4 does not modify the quantity or quality of the antibodies secreted by B cells from infected mice, as it blocks their terminal differentiation to plasma cells and favors memory pathway. It is interesting that the protective effect of IL-4 over B cells from infected mice is mediated, at least partly, by the down-regulation of Fas ligand (FasL) expression, which leads to interference in the apoptosis executed by these B cells through the Fas/FasL death pathway. Accordingly, a marked up-regulation of the "FasL gene repressor" class II transactivator was observed, suggesting that this would be one mechanism underlying the IL-4-mediated FasL down-regulation.

Trypanosoma cruzi induces edematogenic responses in mice and invades cardiomyocytes and endothelial cells in vitro by activating distinct kinin receptor (B1/B2) subtypes

Trypanosoma cruzi, the protozoan that causes Chagas' heart disease, invades endothelial cells in vitro by activating the B2 kinin receptor (B2R). Here, we demonstrate that mice infected with trypomastigotes develop potent edema after treatment with the angiotensin-converting enzyme (ACE) (or kininase II) inhibitor captopril. Experiments performed with specific kinin receptor (B2R/B1R) antagonists and knockout mice revealed that the early-phase (3-h) edema is mediated by the constitutive B2R, whereas the late-phase (24-h) response depends on stimulation of the up-regulated B1R. Given previous evidence that parasite invasion of cells expressing B2R is potentiated by captopril, we investigated the prerequisites for in vitro infection of Chinese hamster ovary cells overexpressing either B1R or B2R, human umbilical vein endothelial cells activated by lipopolysaccharide, and neonatal rat cardiomyocytes. Our results indicate that captopril potentiates parasite invasion regardless of the kinin (B2/B1) activation pathways, whereas DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid (MGTA), an inhibitor of kininase I (carboxypeptidase M/N), selectively decreases parasite infectivity for B1R-expressing cells. These data suggest that formation of the B1R agonist, i.e., [des-Arg] kinins, critically depends on the processing action of kininase I, here proposed as a potential pathogenesis cofactor. Collectively, our data suggest that fluctuations in the levels of kininases may modulate parasite infectivity and pathological outcome in Chagas' disease.

Macrophage signaling by glycosylphosphatidylinositol-anchored mucin-like glycoproteins derived from Trypanosoma cruzi trypomastigotes

Activation of cells from the innate immune system has an important role in host resistance to early infection with the intracellular protozoan parasite, Trypanosoma cruzi. Here we review the studies that have identified and structurally characterized the glycosylphosphatidylinositol (GPI) anchors, as parasite molecules responsible for the activation of cells from the macrophage lineage. We also cover the studies that have identified the receptor, signaling pathways as well as the array of genes expressed in macrophages that are activated by these glycoconjugates. We discuss the possible implications of such response on the host resistance to T. cruzi infection and the pathogenesis of Chagas disease.