Captopril prevents experimental autoimmune myocarditis

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-gamma 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.     

Heat-killed Trypanosoma cruzi induces acute cardiac damage and polyantigenic autoimmunity

Chagas heart disease, caused by the protozoan parasite Trypanosoma cruzi, is a potentially fatal cardiomyopathy often associated with cardiac autoimmunity. T. cruzi infection induces the development of autoimmunity to a number of antigens via molecular mimicry and other mechanisms, but the genesis and pathogenic potential of this autoimmune response has not been fully elucidated. To determine whether exposure to T. cruzi antigens alone in the absence of active infection is sufficient to induce autoimmunity, we immunized A/J mice with heat-killed T. cruzi (HKTC) emulsified in complete Freund's adjuvant, and compared the resulting immune response to that induced by infection with live T. cruzi. We found that HKTC immunization is capable of inducing acute cardiac damage, as evidenced by elevated serum cardiac troponin I, and that this damage is associated with the generation of polyantigenic humoral and cell-mediated autoimmunity with similar antigen specificity to that induced by infection with T. cruzi. However, while significant and preferential production of Th1 and Th17-associated cytokines, accompanied by myocarditis, develops in T. cruzi-infected mice, HKTC-immunized mice produce lower levels of these cytokines, do not develop Th1-skewed immunity, and lack tissue inflammation. These results demonstrate that exposure to parasite antigen alone is sufficient to induce autoimmunity and cardiac damage, yet additional immune factors, including a dominant Th1/Th17 immune response, are likely required to induce cardiac inflammation.     

Autoimmune myocarditis does not require B cells for antigen presentation.

T cells constitute the pathogenic effector cell population in autoimmune myocarditis in BALB/c mice. Using mice rendered deficient for B cells by a targeted disruption to the IgM transmembrane domain or by treatment with anti-IgM Ab from birth, we asked whether B cells are a critical APC in the induction of autoimmune myocarditis. B cell-deficient mice immunized with cardiac myosin develop myocarditis comparable in incidence and severity to that in wild-type mice, suggesting that autoreactive T cells that cause myocarditis in BALB/c mice are activated by macrophages or dendritic cells. Since it does not appear that presentation of cryptic epitopes is critical for the breakdown of self tolerance, potentially pathogenic T cells recognizing dominant myosin epitopes must have escaped tolerization. Either anatomic sequestration of cardiac myosin peptide-MHC complexes or subthreshold presentation of cardiac myosin peptides by conventional APC can explain the survival of these autoreactive T cells.     

Cytokines and cell adhesion receptors in the regulation of immunity to Trypanosoma cruzi

Pathophysiology of Chagas' disease is not completely defined, although innate and adaptative immune responses are crucial. In acute infection some parasite antigens can activate macrophages, and this may result in pro-inflammatory cytokine production, nitric oxide synthesis, and consequent control of parasitemia and mortality. Cell-mediated immunity in Trypanosoma cruzi infection is also modulated by cytokines, but in addition to parasite-specific responses, autoimmunity can be also triggered. Importantly, cytokines may also play a role in the cell-mediated immunity of infected subjects. Finally, leukocyte influx towards target tissues is regulated by cytokines, chemokines, and extracellular matrix components which may represent potential therapeutic targets in infected patients. Here we will discuss recent findings on the role of cytokines, chemokines and extracellular matrix components in the regulation of innate and adaptive immunity during T. cruzi infection.     

TNF/TNFR1 signaling up-regulates CCR5 expression by CD8+ T lymphocytes and promotes heart tissue damage during Trypanosoma cruzi infection: beneficial effects of TNF-alpha blockade

In Chagas disease, understanding how the immune response controls parasite growth but also leads to heart damage may provide insight into the design of new therapeutic strategies. Tumor necrosis factor-alpha (TNF-alpha) is important for resistance to acute Trypanosoma cruzi infection; however, in patients suffering from chronic T. cruzi infection, plasma TNF-alpha levels correlate with cardiomyopathy. Recent data suggest that CD8-enriched chagasic myocarditis formation involves CCR1/CCR5-mediated cell migration. Herein, the contribution of TNF-alpha, especially signaling through the receptor TNFR1/p55, to the pathophysiology of T. cruzi infection was evaluated with a focus on the development of myocarditis and heart dysfunction. Colombian strain-infected C57BL/6 mice had increased frequencies of TNFR1/p55+ and TNF-alpha+ splenocytes. Although TNFR1-/- mice exhibited reduced myocarditis in the absence of parasite burden, they succumbed to acute infection. Similar to C57BL/6 mice, Benznidazole-treated TNFR1-/- mice survived acute infection. In TNFR1-/- mice, reduced CD8-enriched myocarditis was associated with defective activation of CD44+CD62Llow/- and CCR5+ CD8+ lymphocytes. Also, anti-TNF-alpha treatment reduced the frequency of CD8+CCR5+ circulating cells and myocarditis, though parasite load was unaltered in infected C3H/HeJ mice. TNFR1-/- and anti-TNF-alpha-treated infected mice showed regular expression of connexin-43 and reduced fibronectin deposition, respectively. Furthermore, anti-TNF-alpha treatment resulted in lower levels of CK-MB, a cardiomyocyte lesion marker. Our results suggest that TNF/TNFR1 signaling promotes CD8-enriched myocarditis formation and heart tissue damage, implicating the TNF/TNFR1 signaling pathway as a potential therapeutic target for control of T. cruzi-elicited cardiomyopathy.     

Cardiac myosin induces myocarditis in genetically predisposed mice

After infection with coxsackie virus B3 (CB3), H-2 congenic mice on an A- background develop immunologically mediated myocarditis associated with an increased titer of myosin autoantibody, part of which is specific for the cardiac myosin isoform. The present study demonstrates that cardiac myosin itself induces severe myocarditis and high titers of myosin autoantibodies in A/J, A.SW/SnJ, and A.CA/SnJ mice. As in CB3-induced myocarditis, one population of these autoantibodies was specific for cardiac myosin. A.BY/SnJ and B10.A/SgSnJ mice also developed the disease after immunization, but the prevalence and the myosin autoantibody titers were lower. In contrast, C57BL/6J and C57BL/10J mice were resistant to myocarditis induced by cardiac myosin and did not develop increased myosin autoantibodies or cardiac myosin-specific autoantibodies. Immunization with skeletal muscle myosin had no effect compared with controls injected with complete Freund's adjuvant, thereby suggesting that the immunogenic epitopes are unique to the cardiac myosin isoform. Furthermore, we found that susceptibility to myocarditis induced by cardiac myosin is influenced by the major histocompatibility complex and by genes not closely linked to the major histocompatibility complex. Because there are parallels between myocarditis induced by cardiac myosin and that induced by CB3, this new animal model can be used to analyze the pathologic mechanisms in autoimmune heart disease.     

Changes in humoral responses to Trypanosoma cruzi during the course of infection in mice held at elevated temperature.

A parasite-specific, enzyme-linked immunosorbent assay and immunoblot analysis were used to examine the development of humoral immunity in Trypanosoma cruzi-infected C3H mice that survive acute infection when held at elevated environmental temperature. Both parasite-specific antibody levels and numbers of antigens identified increased during infection in mice held at 36 C, with the greatest reactivity measured in sera from mice that had resolved parasitemias. Heat shock of culture forms of T. cruzi resulted in production of different antigens, but there was no strong difference in the antigens recognized by sera from mice held at room temperature and those recognized by sera from mice held at 36 C. Immunoblot analysis using blood-form trypomastigote antigens identified a band of approximately 61 kDa produced by trypomastigotes in mice held at 36 C that was strongly detected by sera from mice held at 36 C. Little if any reactivity to this antigen was observed using sera from mice held at room temperature.     

TLR ligands act directly upon T cells to restore proliferation in the absence of protein kinase C-theta signaling and promote autoimmune myocarditis

The serine/threonine kinase, protein kinase C-theta (PKC-theta), plays a central role in the activation and differentiation of Th2 cells while being redundant in CD4+ and CD8+ antiviral responses. Recent evidence indicates that PKC-theta may however be required for some T cell-driven autoimmune responses. We have investigated the role of PKC-theta in the induction of autoimmune myocarditis induced by either Coxsackie B3 virus infection or immunization with alpha-myosin/CFA (experimental autoimmune myocarditis (EAM)). PKC-theta-deficient mice did not develop EAM as shown by impaired inflammatory cell infiltration into the heart, reduced CD4+ T cell IL-17 production, and the absence of a myosin-specific Ab response. Comparatively, PKC-theta was not essential for both early and late-phase Coxsackie virus-induced myocarditis. We sought to find alternate pathways of immune stimulation that might reconcile the differential requirements for PKC-theta in these two disease models. We found systemic administration of the TLR ligand CpG restored EAM in PKC-theta-deficient mice. CpG could act directly upon TLR9-expressing T cells to restore proliferation and up-regulation of Bcl-x(L), but exogenous IL-6 and TGF-beta was required for Th17 cell differentiation. Taken together, these results indicate that TLR-mediated activation of T cells can directly overcome the requirement for PKC-theta signaling and, combined with the dendritic cell-derived cytokine milieu, can promote the development of autoimmunity.     

Different infective forms trigger distinct immune response in experimental Chagas disease

Although metacyclic and blood trypomastigotes are completely functional in relation to parasite-host interaction and/or target cell invasion, they differ in the molecules present on the surface. Thus, aspects related to the variability that the forms of T. cruzi interacts with host cells may lead to fundamental implications on the immune response against this parasite and, consequently, the clinical evolution of Chagas disease. We have shown that BT infected mice presented higher levels of parasitemia during all the acute phase of infection. Moreover, the infection with either MT or BT forms resulted in increased levels of total leukocytes, monocytes and lymphocytes, specifically later for MT and earlier for BT. The infection with BT forms presented earlier production of proinflammatory cytokine TNF-α and later of IFN-γ by both T cells subpopulations. This event was accompanied by an early cardiac inflammation with an exacerbation of this process at the end of the acute phase. On the other hand, infection with MT forms result in an early production of IFN-γ, with subsequent control in the production of this cytokine by IL-10, which provided to these animals an immunomodulatory profile in the end of the acute phase. These results are in agreement with what was found for cardiac inflammation where animals infected with MT forms showed intense cardiac inflammation later at infection, with a decrease in the same at the end of this phase. In summary, our findings emphasize the importance of taking into account the inoculums source of T. cruzi, since vectorial or transfusional routes of T. cruzi infection may trigger distinct parasite-host interactions during the acute phase that may influence relevant biological aspects of chronic Chagas disease.     

Cutting edge: a critical role for IL-10 in induction of nasal tolerance in experimental autoimmune myocarditis

Appropriate treatment of autoimmune myocarditis following virus infection remains a major clinical problem. Induction of nasal tolerance may provide a new approach to treatment. However, the exact mechanism of nasal tolerance is unknown. To assess the mechanism of nasal tolerance, we examined the role of IL-10 in the induction and suppression of autoimmune myocarditis. First we showed that blocking IL-10 concurrent with nasal administration of Ag abolished the disease-suppressing effect of nasal tolerization. It also led to increased cardiac myosin-specific IL-1 and TNF-alpha production. Then we demonstrated that blocking IL-10 during the effector phase increased not only the incidence and severity of disease but also Ag-specific IL-2, IL-4, and TNF-alpha production as well as cardiac myosin-specific IgG1 and IgG2b production, whereas blocking IL-10 during the induction phase had no effect. This study implicates IL-10 in the induction of nasal tolerance and in limiting inflammation later during the disease process.     

Myosin-induced acute myocarditis is a T cell-mediated disease

The heart is a target organ in several autoimmune diseases, and therefore it is important to understand more about the effector cells involved in immune-mediated mechanisms of myocardial cell death. Because immune T lymphocytes are central to many immune responses, we wanted to study the role of T cells in causing cardiac specific inflammation. We used purified mouse cardiac myosin to cause acute myocarditis in mice. The adoptive transfer of purified T cells from C.B-17 mice with active myocarditis to SCID recipients successfully transferred the disease into SCID hosts. In contrast, transfer of serum with high-titer antimyosin antibodies to SCID hosts did not cause myocarditis. Using mAb to deplete A/J mice of CD4+ T cells, we showed that these mice were protected against the induction of myocarditis. Depletion of CD8+ T cells reduced the severity of inflammation but did not prevent induction of myocarditis. We were also able to prevent the induction of myocarditis using major histocompatibility class II protein-binding, nonimmunogenic, competitor peptides. These blocking studies also indicated that in H-2k mice, myocarditis is an I-Ak-restricted disease, and provided further evidence that CD4+ T cells are critical to the induction of disease. Together, these studies provide direct evidence that myosin-induced myocarditis is a T cell-mediated disease.     

Behavior of atrial natriuretic factor in an experimental model of Trypanosoma cruzi infection in rats

Enhanced atrial natriuretic factor (ANF) production by the heart is related to hemodynamic overload, cardiac growth, and hypertrophy. The heart is one of the most affected organs during Trypanosoma cruzi infection. We tested the hypothesis that myocarditis produced by parasite infection alters the natriuretic peptide system by investigating the behavior of plasma ANF during the acute and chronic stages of T. cruzi infection in rats. Sprague-Dawley rats were infected with T. cruzi clone Sylvio-X10/7. Cardiac morphology showed damage to myocardial cells and lymphocyte infiltration in the acute phase; and fibrosis and cell atrophy in the chronic period. Plasma ANF levels (radioimmunoassay) were significantly higher in acute (348 +/- 40 vs. 195 +/- 36 pg/ml, P < 0.05, n = 17) and chronic T. cruzi myocarditis (545 +/- 81 vs. 229 +/- 38 pg/ml, P < 0.001, n = 11) than in their respective controls (n = 10 and 14). Rats in the chronic phase also showed higher levels than rats in the acute phase (P < 0.01). The damage of myocardial cells produced by the parasite and the subsequent inflammatory response could be responsible for the elevation of plasma ANF during the acute period of T. cruzi infection. The highest plasma ANF levels found in chronically infected rats could be derived from the progressive failure of cardiac function.     

Trypanosoma cruzi: maintenance of parasite-specific T cell responses in lymph nodes during the acute phase of the infection

Mice infected with 5 x 10(3) forms of Trypanosoma cruzi showed a transient, but severe impairment of in vitro spleen cell responses to parasite antigens and to Concanavalin A (Con A). In contrast, inguinal and periaortic lymph node (LN) cells displayed high parasite-specific proliferative responses and only a partial reduction of the Con A-induced proliferation during the acute and chronic phases of infection. Lymphocytes that underwent blastic transformation in T. cruzi-stimulated cell cultures were of the L3T4+ phenotype. Suppression of spleen cell responses occurred in the acute phase whether mice were infected with high (3 x 10(5] or low (5 x 10(3] doses of T. cruzi by intraperitoneal or subcutaneous route. Suppression of the T. cruzi-specific proliferative response of LN cells was only observed in mice infected with high subcutaneous inocula. This suppression, however, was restricted to the LNs draining the site of inoculation without affecting distant LNs. Supernatants from parasite-stimulated proliferating LN cells displayed low or undetectable T cell growth factor (TCGF) activity, in contrast with the high TCGF levels found in supernatants of the same cells stimulated with Con A. Low levels of TCGF were also detected in cultures of LN cells from mice immunized with T. cruzi extracts. Neither the T. cruzi antigen used for in vitro stimulation nor the LN cell supernatants from infected mice inhibited TCGF activity. These findings indicate that (1) parasite-specific responses are present in the LN compartment throughout the acute phase of T. cruzi infection in mice and (2) the proliferative response of L3T4+ LN cells from infected mice to T. cruzi antigens is not associated with a high TCGF secretory response.     

Trans-sialidase recombinant protein mixed with CpG motif-containing oligodeoxynucleotide induces protective mucosal and systemic trypanosoma cruzi immunity involving CD8+ CTL and B cell-mediated cross-priming

The Trypanosoma cruzi trans-sialidase (TS) is a unique enzyme with neuraminidase and sialic acid transfer activities important for parasite infectivity. The T. cruzi genome contains a large family of TS homologous genes, and it has been suggested that TS homologues provide a mechanism of immune escape important for chronic infection. We have investigated whether the consensus TS enzymatic domain could induce immunity protective against acute and chronic, as well as mucosal and systemic, T. cruzi infection. We have shown that: 1) TS-specific immunity can protect against acute T. cruzi infection; 2) effective TS-specific immunity is maintained during chronic T. cruzi infection despite the expression of numerous related TS superfamily genes encoding altered peptide ligands that in theory could promote immune tolerization; and 3) the practical intranasal delivery of recombinant TS protein combined with a ssDNA oligodeoxynucleotide (ODN) adjuvant containing unmethylated CpG motifs can induce both mucosal and systemic protective immunity. We have further demonstrated that the intranasal delivery of soluble TS recombinant Ag combined with CpG ODN induces both TS-specific CD4(+) and CD8(+) T cells associated with vaccine-induced protective immunity. In addition, optimal protection induced by intranasal TS Ag combined with CpG ODN requires B cells, which, after treatment with CpG ODN, have the ability to induce TS-specific CD8(+) T cell cross-priming. Our results support the development of TS vaccines for human use, suggest surrogate markers for use in future human vaccine trials, and mechanistically identify B cells as important APC targets for vaccines designed to induce CD8(+) CTL responses.     

Changes in cell populations and immunoglobulin-producing cells in the spleens of mice infected with Trypanosoma cruzi: correlations with parasite-specific antibody response

Infection of mice with Trypanosoma cruzi elicits the production of parasite-specific antibodies which reach high levels and remain elevated for at least 105 days of infection. The more susceptible C3H(He) mouse actually has a higher level of "natural" antibodies for T. cruzi but may show a greater lag time in the production of antibodies in response to infection than the more resistant C57BL/6 mouse. Comparison of the kinetics of antibody production against T. cruzi and the numbers of immunoglobulin-producing cells in the spleen during the course of infection suggests that a large number of the immunoglobulin-producing cells are probably producing antibodies directed against the parasite and are not the result of an exhaustive polyclonal B-cell activation. Cell numbers in the spleen change dramatically both in total numbers and in the percentage of different cell types during infection with T. cruzi. The percentage of T cells in the spleen remains relatively unchanged throughout infection in both mouse strains tested but numbers of Ig-positive cells decrease markedly during the acute phase of infection while macrophage numbers increase up to sixfold. Cell numbers and proportions of B cells, T cells, and macrophages return to near normal values by 105 days of infection in the C57BL/6 mouse.     

Anti-human cardiac myosin autoantibodies in Kawasaki syndrome.

Kawasaki syndrome (KS) is the major cause of acquired heart disease in children. Although acute myocarditis is observed in most patients with KS, its pathogenesis is unknown. Because antimyosin autoantibodies are present in autoimmune myocarditis and rheumatic carditis, the purpose of the current study was to determine whether anticardiac myosin Abs might be present during the acute stage of KS. Sera from KS patients as well as age-matched febrile controls and normal adults were compared for reactivity with human cardiac myosin in ELISAs and Western blot assays. A total of 5 of 13 KS sera, as compared with 5 of 8 acute rheumatic fever sera, contained Ab titers to human cardiac myosin that were significantly higher than those found in control sera. Both cardiac and skeletal myosins were recognized in the ELISA by KS sera, although stronger reactivity was observed to human cardiac myosin. Only IgM antimyosin Abs from KS sera were significantly elevated relative to control sera. KS sera containing antimyosin Abs recognized synthetic peptides from the light meromyosin region of the human cardiac myosin molecule and had a different pattern of reactivity than acute rheumatic fever sera, further supporting the association of antimyosin Ab with KS. These Abs may contribute to the pathogenesis of acute myocarditis found in patients with KS.     

Immunopathology of cardiomyopathy in the experimental Chagas disease

The mechanisms by which Trypanosoma cruzi causes cardiomyopathy and induces neuronal destruction are discussed in this paper. The results suggest that autoimmunity in the chronic phase is the main cause of the progressive cardiac destruction, and that autoreactivity is restricted to the CD4+ T cell compartment. During the acute phase, the neuronal and cardiac fiber destruction occurs when ruptured parasite nests release T. cruzi antigens that bind to the cell surface in the vicinity which become targets for the cellular and humoral immune response against T. cruzi. The various factors involved in the genesis of autoimmunity in chronic T. cruzi infection include molecular mimicry, presentation of self-antigens and imbalance of immune regulation.     

IL-10 limits parasite burden and protects against fatal myocarditis in a mouse model of Trypanosoma cruzi infection

Chagas' disease is a zoonosis prevalent in Latin America that is caused by the protozoan Trypanosoma cruzi. The immunopathogenesis of cardiomyopathy, the main clinical problem in Chagas' disease, has been extensively studied but is still poorly understood. In this study, we systematically compared clinical, microbiologic, pathologic, immunologic, and molecular parameters in two mouse models with opposite susceptibility to acute myocarditis caused by the myotropic Colombiana strain of T. cruzi: C3H/HeSnJ (100% mortality, uncontrolled parasitism) and C57BL/6J (<10% mortality, controlled parasitism). T. cruzi induced differential polarization of immunoregulatory cytokine mRNA expression in the hearts of C57BL/6J versus C3H/HeSnJ mice; however, most differences were small. The difference in IL-10 expression was exceptional (C57BL/6J 8.7-fold greater than C3H/HeSnJ). Consistent with this, hearts from infected C57BL/6J mice, but not C3H/HeSnJ mice, had a high frequency of total IL-10-producing CD8(+) T cells and both CD4(+) and CD8(+) subsets of IFN-γ(+)IL-10(+) double-producing T cells. Furthermore, T. cruzi infection of IL-10(-/-) C57BL/6J mice phenocopied fatal infection in wild-type C3H/HeSnJ mice with complete loss of parasite control. Adoptive transfer experiments indicated that T cells were a source of protective IL-10. Thus, in this system, IL-10 production by T cells promotes T. cruzi control and protection from fatal acute myocarditis.     

Pathology of intracardiac nerves in experimental Chagas disease

Severe destruction of intrinsic cardiac nerves has been reported in experimental acute Chagas myocarditis, followed by extensive regeneration during the chronic phase of the infection. To further study this subject, the sympathetic and para-sympathetic intracardiac nerves of mice infected with a virulent Trypanosoma cruzi strain were analyzed, during acute and chronic infection, by means of histological, histochemical, morphometric and electron microscopic techniques. No evidences of destructive changes were apparent. Histochemical demonstration for acetylcholinesterase and catecholamines did not reveal differences in the amount and distribution of intracardiac nerves, in mice with acute and chronic Chagas myocarditis or in non-infected controls. Mild, probably reversible ultrastructural neural changes were occasionally present, especially during acute myocarditis. Intrinsic nerves appeared as the least involved cardiac structure during the course of experimental Chagas disease in mice.     

CD4 T cells play major effector role and CD8 T cells initiating role in spontaneous autoimmune myocarditis of HLA-DQ8 transgenic IAb knockout nonobese diabetic mice

In humans, spontaneous autoimmune attack against cardiomyocytes often leads to idiopathic dilated cardiomyopathy (IDCM) and life-threatening heart failure. HLA-DQ8 transgenic IAb knockout NOD mice (NOD.DQ8/Ab(0); DQA1*0301, DQB1*0302) develop spontaneous anticardiomyocyte autoimmunity with pathology very similar to human IDCM, but why the heart is targeted is unknown. In the present study, we first investigated whether NOD/Ab(0) mice transgenic for a different DQ allele, DQ6, (DQA1*0102, DQB1*0602) would also develop myocarditis. NOD.DQ6/Ab(0) animals showed no cardiac pathology, implying that DQ8 is specifically required for the myocarditis phenotype. To further characterize the cellular immune mechanisms, we established crosses of our NOD.DQ8/Ab(0) animals with Rag1 knockout (Rag1(0)), Ig H chain knockout (IgH(0)), and beta(2)-microglobulin knockout (beta(2)m(0)) lines. Adoptive transfer of purified CD4 T cells from NOD.DQ8/Ab(0) mice with complete heart block (an indication of advanced myocarditis) into younger NOD.DQ8/Ab(0) Rag1(0) animals induced cardiac pathology in all recipients, whereas adoptive transfer of purified CD8 T cells or B lymphocytes had no effect. Despite the absence of B lymphocytes, NOD.DQ8/Ab(0)IgH(0) animals still developed complete heart block, whereas NOD.DQ8/Ab(0)beta(2)m(0) mice (which lack CD8 T cells) failed to develop any cardiac pathology. CD8 T cells (and possibly NK cells) seem to be necessary to initiate disease, whereas once initiated, CD4 T cells alone can orchestrate the cardiac pathology, likely through their capacity to recruit and activate macrophages. Understanding the cellular immune mechanisms causing spontaneous myocarditis/IDCM in this relevant animal model will facilitate the development and testing of new therapies for this devastating disease.