Infection with Trypanosoma cruzi, the agent of Chagas' disease, may induce antibodies and T cells reactive with self antigens (autoimmunity). Because autoimmunity is generally thought to develop during the chronic phase of infection, one hypothesis is that autoimmunity develops only after long-term, low-level stimulation of self-reactive cells. However, preliminary reports suggest that autoimmunity may begin during acute T. cruzi infection. The goal of the present study was to investigate whether cardiac autoimmunity could be observed during acute T. cruzi infection. A/J mice infected with the Brazil strain of T. cruzi for 21 days developed severe myocarditis, accompanied by humoral and cellular autoimmunity. Specifically, T. cruzi infection induced immunoglobulin G (IgG) autoantibodies and delayed type hypersensitivity (DTH) to cardiac myosin. This autoimmunity resembles that which develops in A/J mice immunized with myosin in complete Freund's adjuvant in that myosin-specific antibodies and DTH responses both develop by 21 days postinfection or postimmunization. While the levels of myosin IgG in T. cruzi-infected mice were slightly lower than those in myosin-immunized mice, the magnitude of myosin DTH in the two groups was statistically equivalent. In contrast, C57BL/6 mice, which are resistant to myosin-induced myocarditis and its associated autoimmunity, developed undetectable or low levels of myosin IgG and did not exhibit myosin DTH or myocarditis upon T. cruzi infection. Therefore, humoral and cellular cardiac autoimmunity can develop during acute T. cruzi infection in the genetically susceptible host.

Captopril, an angiotensin-converting enzyme inhibitor, is widely used in the treatment of a variety of cardiomyopathies, but its effect on autoimmune myocarditis has not been addressed experimentally. We investigated the effect of captopril on myosin-induced experimental autoimmune myocarditis. A/J mice, immunized with syngeneic cardiac myosin, were given 75 mg/L of captopril in their drinking water. Captopril dramatically reduced the incidence and severity of myocarditis, which was accompanied by a reduction in heart weight to body weight ratio and heart weight. Captopril specifically interfered with cell-mediated immunity as myosin delayed-type hypersensitivity (DTH) was reduced, while anti-myosin Ab production was not affected. Captopril-treated, OVA-immunized mice also exhibited a decrease in OVA DTH. In myosin-immunized, untreated mice, injection of captopril directly into the test site also suppressed myosin DTH. Interestingly, captopril did not directly affect Ag-specific T cell responsiveness because neither in vivo nor in vitro captopril treatment affected the proliferation, IFN-γ secretion, or IL-2 secretion by Ag-stimulated cultured splenocytes. These results indicate that captopril ameliorates experimental autoimmune myocarditis and may act, at least in part, by interfering with the recruitment of cells to sites of inflammation and the local inflammatory environment.

The specificity and function of T helper (Th) immune responses underlying the induction, progression, and resolution of experimental autoimmune myocarditis (EAM) in A/J mice are unclear. Published data suggest involvement of both Th1 and Th2 responses in EAM; however, the previous inability to assess antigen-specific in vivo and in vitro T cell responses in cardiac myosin immunized animals has confounded our understanding of this important model of autoimmune myocarditis. The goal of our study was to develop an alternative model of EAM based on a recombinant fragment of cardiac myosin, in hopes that the recombinant protein will permit measurement of functional T cell responses that is not possible with purified native protein. A/J mice immunized with a recombinant fragment of cardiac myosin spanning amino acids 1074-1646, termed Myo4, developed severe myocarditis characterized by cardiac hypertrophy, massive mononuclear cell infiltration and fibrosis, three weeks post-immunization. The mice also developed an IgG1 dominant humoral immune response specific for both Myo4 and purified cardiac myosin. The in vitro stimulation of splenocytes harvested from Myo4-immunized animals with Myo4 resulted in cellular proliferation with preferential production of the Th1-and Th17-associated cytokines, IFN-γ, IL-17 and IL-6, respectively. Production of IL-4 was negligible by comparison. This study describes a new model of EAM, inducible by immunization with a specific fragment of cardiac myosin, from which antigenspecific analyses reveal an importance for both Th1 and Th17 immunity.

Trypanosoma cruzi is the protozoan parasite that causes Chagas' heart disease, a potentially fatal cardiomyopathy prevalent in Central and South America. Infection with T. cruzi induces cardiac myosin autoimmunity in susceptible humans and mice, and this autoimmunity has been suggested to contribute to cardiac inflammation. To address how T. cruzi induces cardiac myosin autoimmunity, we investigated whether immunity to T. cruzi antigens could induce cardiac myosin-specific autoimmunity in the absence of live parasites. We immunized A/J mice with a T. cruzi Brazil-derived protein extract emulsified in complete Freund's adjuvant and found that these mice developed cardiac myosin-specific delayed-type hypersensitivity (DTH) and autoantibodies in the absence of detectable cardiac damage. The induction of autoimmunity was specific since immunization with extracts of the related protozoan parasite Leishmania amazonensis did not induce myosin autoimmunity. The immunogenetic makeup of the host was important for this response, since C57BL/6 mice did not develop cardiac myosin DTH upon immunization with T. cruzi extract. Perhaps more interesting, mice immunized with cardiac myosin developed T. cruzi-specific DTH and antibodies. This DTH was also antigen specific, since immunization with skeletal myosin and myoglobin did not induce T. cruzi-specific immunity. These results suggest that immunization with cardiac myosin or T. cruzi antigen can induce specific, bidirectionally cross-reactive immune responses in the absence of detectable cardiac damage.Trypanosoma cruzi is the protozoan parasite that causes Chagas' heart disease (CHD), a potentially fatal cardiomyopathy resulting in dilated tissue. Approximately 16 million people are infected with this protozoan parasite, and 120 million are at risk of infection in Central and South America (28). CHD develops in roughly one-third of T. cruzi-infected individuals as an acute or chronic myocarditis of variable degree (reviewed in reference 39). Among the various mechanisms invoked to explain the pathogenesis of CHD, autoimmunity is one that both has been supported by much experimental evidence and has received much criticism. There is no doubt that autoimmunity results from chronic T. cruzi infection of humans and experimental animals. The questions are (i) whether this autoimmunity is pathogenic and (ii) by what mechanism(s) autoimmunity is induced. The debate surrounding this issue is long-standing (reviewed in references 17, 22, 39, and 40).T. cruzi infection induces humoral and cellular autoimmunity to a diverse set of autoantigens (reviewed in references 17 and 22), including cardiac myosin. Myosin-specific autoimmunity is induced in both humans (8) and experimental models (24) upon T. cruzi infection. In previous work (24), it was found that within weeks of infection, A/J mice acutely infected with T. cruzi developed severe myocarditis accompanied by myosinspecific delayed-type hypersensitivity (DTH) and antibody production. Autoimmunity to cardiac myosin has also been rep...

Background— Captopril, an angiotensin-converting enzyme inhibitor, is commonly prescribed to patients with Chagas heart disease (CHD). There are few human studies and no animal studies on the effects of captopril in CHD. We investigated the effects of captopril on myocarditis and the host immune response to Trypanosoma cruzi in an experimental model of acute CHD. Methods and Results— A/J mice infected with Brazil strain of T cruzi developed acute myocarditis by day 21 after infection, consisting of severe focal inflammation, necrosis, fibrosis, and T cruzi pseudocysts. Administration of captopril (5 mg/L in the water) significantly reduced necrosis and fibrosis in infected mice. Increasing the captopril dose also led to a decrease in inflammation. Captopril did not affect overall mortality but did delay death while having no effect on parasitemia or cardiac parasite load. Treatment did not affect humoral immunity against T cruzi or cardiac myosin (autoimmunity) but did decrease delayed-type hypersensitivity responses against both antigens. Interestingly, increasing the dose of captopril induced mortality in infected mice in a dose-dependent manner. Mortality was apparently not due to T cruzi because neither parasitemia nor cardiac parasitosis was affected. The combination of captopril and infection may have impaired renal function because these mice had increased water consumption, decreased body mass, and increased serum BUN/creatinine ratio. Conclusions— Captopril ameliorates the myocarditis associated with acute T cruzi infection.