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

Abstract

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.

FIG. 1.

Intensity of inflammation in the heart, liver, and striated muscle of chronically infected mice from different strains. Mice were infected i.p. with 10⁶ Sylvio X10/4 trypomastigotes, and the infiltrated areas were evaluated at day 200 postinfection, as described in Materials and Methods. Each bar represents the mean ± SE (error bar) of individual values (n = 5).

FIG. 2.

Examples of lesions in the heart, liver, and striated muscle of C3H/HePAS and A/J mice infected for 200 days with 10⁶ Sylvio X10/4 trypomastigotes. (A) Heart section of a C3H/HePAS infected mouse displaying intense cardiac pathology with pronounced mononuclear infiltration at the pericadium and myocardium. (B) Heart section of an A/J infected mouse showing no inflammation. (C) Absence of liver lesions in a C3H/HePAS infected mouse. (D) Intense hepatitis in an A/J infected mouse. Inflammatory infiltrates of different intensities in the striated muscle of C3H/HePAS (E)- and A/J (F)-infected mice. Bar, 50 μm; magnification, ×17.

FIG. 3.

Parasite nest in the myocardium of C3H/HePAS mice infected for 200 days with 10⁶ Sylvio X10/4 trypomastigotes. A magnified picture of the pseudocyst can be seen in the insert. Bar, 50 μm; magnification, ×17.

FIG. 4.

Analysis of inflammatory infiltrates in the heart, liver, and striated muscle of chronically infected C3H/HePAS and A/J mice. Cumulative data of various experiments done at various times from day 120 to 600 after infection with 10⁶ Sylvio X10/4 trypomastigotes are shown. Each dot represents one mouse and mean values are indicated by horizontal lines. Infiltrated areas were evaluated as described in Materials and Methods.

FIG. 5.

Cumulative mortality curves of C3H/HePAS and A/J mice infected i.p. with 10⁶ Sylvio X10/4 trypomastigotes/mouse (20 mice/group).

FIG. 6.

Analysis of inflammatory infiltrates in the heart and liver of chronically infected F₁ (A/J × C3H/HePAS) and F₂ (A/J × C3H/HePAS) mice. Mice from the F₁ and F₂ generations, as well as from parental controls, were infected for 200 days with 10⁶ Sylvio X10/4 trypomastigotes. Each dot represents one mouse, and median valuesare indicated by horizontal lines. Infiltrated areas were evaluated as described in Materials and Methods.

FIG. 7.

Genetic heterogeneity in heart and liver pathology of F₂ (A/J × C3H/HePAS) chronically infected mice. The figure represents the correlation of heart and liver pathologies in 71 mice at day 200 of infection. Tissue inflammation is represented on each axis as the log₁₀ of the infiltrated area.

FIG. 8.

Parasite-specific antibodies in the serum of C3H/HePAS, A/J, F₁ (A/J × C3H/HePAS), and F₂ (A/J × C3H/HePAS) chronically infected mice and in noninfected age-matched C3H/HePAS and A/J controls. Mice from the F₁ and F₂ generations, as well as from parental controls, were infected with 10⁶ Sylvio X10/4 trypomastigotes. At day 200 after infection, mice were bled and their sera were analyzed by ELISA with T. cruzi antigen to determine the level of specific IgG2a and IgG1 antibodies.