Infection by the Sylvio X10/4 clone of Trypanosoma cruzi: relevance of a low-virulence model of Chagas' disease.

The physiopathology of Chagas' disease has been largely defined in murine infections with virulent strains which partially represent parasite diversity. This report reviews our studies with Sylvio X10/4 parasites, a Trypanosoma cruzi clone that induces no acute phase but in C3H/He mice leads to chronic myocarditis resembling the human disease.

Islet expression of M3 uncovers a key role for chemokines in the development and recruitment of diabetogenic cells in NOD mice.

OBJECTIVE: Type 1 diabetes is an autoimmune disease characterized by a local inflammatory reaction in and around islets followed by selective destruction of insulin-secreting beta-cells. We tested the hypothesis that chemokines affect different mechanisms responsible for the development of diabetes in NOD mice. RESEARCH DESIGN AND METHODS: We examined chemokine expression in islets of NOD mice and tested their functional relevance to development of diabetes using transgenic mice expressing the mouse herpesvirus 68-encoded chemokine decoy receptor M3 (NOD-M3 mice) in insulin-secreting beta-cells. RESULTS: Multiple chemokines were expressed in pancreatic islets of NOD mice before development of diabetes. Islet-specific expression of the pan-chemokine inhibitor M3 dramatically reduced leukocyte infiltration and islet destruction and completely blocked development of diabetes in NOD-M3 mice. M3 blocked diabetes by inhibiting the priming of diabetogenic cells in the pancreatic lymph nodes and their recruitment into the islets. This effect was specific to the pancreatic islets because M3 expression did not affect other ongoing autoimmune processes. CONCLUSIONS: These results demonstrate that chemokines mediate afferent and efferent immunity in type 1 diabetes and suggest that broad chemokine blockade may represent a viable strategy to prevent insulitis and islet destruction.

The human herpesvirus 8 chemokine receptor vGPCR triggers autonomous proliferation of endothelial cells.

We have used a novel conditional transgenic system to study the mechanisms of angioproliferation induced by viral G protein-coupled receptor (vGPCR), the constitutively active chemokine receptor encoded by human herpesvirus 8 (HHV8, also known as Kaposi sarcoma herpesvirus). Using this system, we were able to control temporal expression of vGPCR and to monitor its expression in situ via the use of the surrogate marker LacZ. Upon treatment with doxycycline (DOX), cells expressing vGPCR and LacZ (vGPCR/LacZ(+) cells) progressively accumulated in areas where angioproliferation was observed. Sorted vGPCR/LacZ(+) cells from angiogenic lesions expressed markers characteristic of endothelial progenitor cells, produced angiogenic factors, and proliferated in vitro. Prolonged treatment of transgenic mice with DOX led to development of tumors in the skin of ears, tail, nose, and paws. vGPCR/LacZ(+) cells were frequent in early lesions but scarce within these tumors. Finally, transfer of vGPCR/LacZ(+) cells into Rag1(-/-) mice treated with DOX led to angioproliferation and, with time, to development of tumors containing both vGPCR/LacZ(+) and vGPCR/LacZ(-) cells. Taken together, these results indicate that vGPCR triggers angioproliferation directly and suggest a novel role for this molecule in the pathogenesis of Kaposi sarcoma.

The human herpes virus 8-encoded chemokine receptor is required for angioproliferation in a murine model of Kaposi's sarcoma.

Kaposi's sarcoma (KS)-associated herpesvirus or human herpes virus 8 is considered the etiological agent of KS, a highly vascularized neoplasm that is the most common tumor affecting HIV/AIDS patients. The KS-associated herpesvirus/human herpes virus 8 open reading frame 74 encodes a constitutively active G protein-coupled receptor known as vGPCR that binds CXC chemokines with high affinity. In this study, we show that conditional transgenic expression of vGPCR by cells of endothelial origin triggers an angiogenic program in vivo, leading to development of an angioproliferative disease that resembles KS. This angiogenic program consists partly in the expression of the angiogenic factors placental growth factor, platelet-derived growth factor B, and inducible NO synthase by the vGPCR-expressing cells. Finally, we show that continued vGPCR expression is essential for progression of the KS-like phenotype and that down-regulation of vGPCR expression results in reduced expression of angiogenic factors and regression of the lesions. Together, these findings implicate vGPCR as a key element in KS pathogenesis and suggest that strategies to block its function may represent a novel approach for the treatment of KS.

Challenge of Trypanosoma cruzi chronically infected mice with trypomastigotes activates the immune system and reduces subpatent parasitemia levels.

Challenge of 1-yr Trypanosoma cruzi chronically infected mice with trypomastigotes results in a consistent reduction of parasite dissemination that correlates with spleen activation and increase in the anti-T. cruzi effector immune mechanisms. That is, parasite challenge results not only in elimination of the inoculum but also in a drastic decrease in basal subpatent parasitemia levels as revealed by transferring blood samples to immunosuppressed mice. Parasite elimination correlated with (1) a brief and intense burst in the ability of spleen cells to produce interferon-gamma, (2) an increase in total IgG2a-producing spleen cells, (3) higher parasite-specific IgG2a serum levels, and (4) an accumulation of non-B, non-T class II+ cells in the spleen. Furthermore, challenged, chronically infected mice had increased numbers of B, CD4+, and CD8+ large spleen cells. Besides reinforcing the activation of protective Th1 effector mechanisms, challenge with T. cruzi also induced Th2 effector molecules, such as interleukin (IL)-10 and IL-4, and IL-4-dependent IgG1. Our results are the first evidence that the immune system of T. cruzi chronically infected mice can be optimized in its ability to restrict parasite dissemination, opening the possibility that therapeutic vaccination could be used to reduce the parasite load and pathology of patients with chronic Chagas' disease.

Pathology affects different organs in two mouse strains chronically infected by a Trypanosoma cruzi clone: a model for genetic studies of Chagas' disease.

Chagas' disease is a chronic infection caused by Trypanosoma cruzi and represents an important public health burden in Latin America. Frequently the disease evolves undetectable for decades, while in a significant fraction of the affected individuals it culminates in death by heart failure. Here, we describe a novel murine model of the chronic infection with T. cruzi using a stable clone isolated from a human patient (Sylvio X10/4). The infection in the C3H/HePAS mouse strain progresses chronically and is mainly characterized by intense cardiac inflammatory lesions that recapitulate the chronic cardiac pathology observed in the human disease. Moderate striated muscle lesions are also present in C3H/HePAS mice. Viable parasites are detected and recovered from the chronic heart lesions of C3H/HePAS mice, supporting the current notion that development of heart pathology in Chagas' disease is related to parasite persistence in the inflamed tissue. By contrast, in infected A/J mice, chronic inflammatory lesions are targeted to the liver and the skeletal muscle, while pathology and parasites are undetectable in the heart. The phenotypic analysis of F(1) (A/J x C3H/HePAS) and F(2) (A/J x C3H/HePAS) mice suggests that the genetic predisposition to develop the inflammatory lesions caused by T. cruzi (Sylvio X10/4 clone) is heterogeneous because the heart and liver pathology segregate in the F(2) generation. These findings raise the hypothesis that the pathology heterogeneity observed in humans with Chagas' disease (absence and presence of cardiac or digestive chronic lesions) may be attributable to host genetic factors.

Impaired macrophage responses may contribute to exacerbation of blood-stage Plasmodium chabaudi chabaudi malaria in interleukin-12-deficient mice.

Aiming to clarify the role of endogenous interleukin-12 (IL-12) in protective immunity against blood stages of Plasmodium chabaudi chabaudi (AS), we evaluated the course of infection in IL-12p40 gene knockout (IL-12p40KO) and wild-type (WT) C57BL/6 mice, focusing (1) on the ability of T cells to develop adequate type 1 responses and (2) on the potentiality of macrophages to respond to parasites, interferon-gamma (IFN-gamma), or both. We observed that IL-12p40KO mice develop significantly higher parasitemias during the acute infection, although mice from both groups clear the parasites within a month and similarly eliminate a secondary challenge. Thus, fully protective immunity to P. c. chabaudi can be generated in the absence of IL-12. However, this cytokine may promote parasite control during the early phase of infection. The increased acute parasitemia of IL-12p40KO mice was associated with both impaired IFN-gamma and nitric oxide (NO) response by spleen cells. Because stimulation with recombinant IFN-gamma (rIFN-gamma) failed to improve the NO response in IL-12p40KO macrophages, we investigated whether these cells have an intrinsic defect. Analysis of peritoneal macrophages revealed that IL-12p40KO cells produce higher levels of transforming growth factor-beta1 (TGF-beta1) compared with WT cells and respond to infected erythrocytes or rIFN-gamma by releasing little NO. Moreover, IL-12p40KO macrophages had a severely impaired ability to internalize opsonized infected erythrocytes, suggesting that the low effector profile assumed by these cells may compromise antibody-mediated immunity. Taken together, our results support the idea that the absence of IL-12p40 not only affects IFN-gamma production but also has deep consequences in macrophage effector functions that may contribute to exacerbation of the early phase of P. c. chabaudi malaria.