A peptide fragment of beta cardiac myosin heavy chain (beta-CMHC) can provoke autoimmune myocarditis as well as the corresponding alpha cardiac myosin heavy chain (alpha-CMHC) fragment

Autoimmune myocarditis, valvulitis, and cardiomyopathy

Myocarditis and valvulitis are inflammatory diseases affecting myocardium and valve. Myocarditis, a viral-induced disease of myocardium, may lead to dilated cardiomyopathy and loss of heart function. Valvulitis leads to deformed heart valves and altered blood flow in rheumatic heart disease. Animal models recapitulating these diseases are important in understanding the human condition. Cardiac myosin is a major autoantigen in heart, and antibodies and T cells to cardiac myosin are evident in inflammatory heart diseases. This unit is a practical guide to induction and evaluation of experimental autoimmune myocarditis (EAM) in several mouse strains and the Lewis rat. Purification protocols for cardiac myosin and protocols for induction of EAM by cardiac myosin and its myocarditis-producing peptides, and coxsackievirus CVB3, are defined. Protocols for assessment of myocarditis and valvulitis in humans and animal models provide methods to define functional autoantibodies targeting cardiac myosin, β-adrenergic, and muscarinic receptors, and their deposition in tissues.

Role of impaired central tolerance to α-myosin in inflammatory heart disease

For more than a half century, autoimmunity has been linked to a diverse array of heart diseases, including rheumatic carditis, myocarditis, Chagas' cardiomyopathy, post-myocardial infarction (Dressler's) syndrome, and idiopathic dilated cardiomyopathy. Why the heart is targeted by autoimmunity in these seemingly unrelated conditions has remained enigmatic. Here, we discuss our recent studies indicating that this susceptibility is mediated by impaired negative selection of autoreactive α-myosin heavy-chain-specific CD4(+) T cells in the thymus of both mice and humans. We describe how this process may place the heart at increased risk for autoimmune attack following ischemic or infectious injury, providing a rationale for the development of antigen-specific tolerogenic therapies.

Immune modulation in heart failure: past challenges and future hopes

Immune-modulation therapy has had great success in various inflammatory diseases. Despite the promising results of preliminary studies in anti-tumor necrosis factor-α therapies, large randomized studies have lacked positive clinical outcomes in patients with heart failure. These results have led to the idea that therapies directed toward specific inflammatory mediators may not be the answer and lead us toward the development of novel anti-inflammatory strategies that may involve a broader spectrum of inflammatory mediators. Therapeutic plasma exchange has been demonstrated as a safe treatment, and preliminary outcomes led us to develop new treatment schemes.

Induction of cardiac autoimmunity in Chagas heart disease: A case for molecular mimicry

Up to 18 million of individuals are infected by the protozoan parasite Trypanosoma cruzi in Latin America, one third of whom will develop chronic Chagas disease cardiomyopathy (CCC) up to 30 years after infection. Cardiomyocyte destruction is associated with a T cell-rich inflammatory infiltrate and fibrosis. The presence of such lesions in the relative scarcity of parasites in the heart, suggested that CCC might be due, in part, to a postinfectious autoimmune process. Over the last two decades, a significant amount of reports of autoimmune and molecular mimicry phenomena have been described in CCC. The authors will review the evidence in support of an autoimmune basis for CCC pathogenesis in humans and experimental animals, with a special emphasis on molecular mimicry as a fundamental mechanism of autoimmunity.

Evidence for activation of immune system in heart failure: is there a role for anti-inflammatory therapy?

PURPOSE OF REVIEW

The efficacy of already established heart failure therapeutics limits new developments; however, there are still fertile grounds for growth with a better understanding of often overlooked mechanisms of disease. We will review evidence on inflammation and components of the inflammatory process occurring in patients with chronic heart failure, review different therapeutic techniques such as intravenous immunoglobin, plasmapheresis and immuno-adsorption.

RECENT FINDINGS

The use of highly specific anti-inflammatory therapeutic strategies in large randomized trials such as anti-TNF-alpha has failed to show clinical benefits; however, by taking a broad spectrum anti-inflammatory approach, strategies as in the ACCLAIM trial have been effective in improving the outcome in a select group of patients.

SUMMARY

There is substantial evidence of immune modulation promoting the downregulation of inflammatory cytokines thus increasing several important and potentially therapeutic anti-inflammatory cytokines. It will be necessary to design large multicenter trials to overcome the expected improvements of current therapies, which may overshadow results, and to finally elucidate the therapeutic contributions of immune modulation in heart failure.

Protection against experimental autoimmune myocarditis is mediated by interleukin-10-producing T cells that are controlled by dendritic cells

Experimental autoimmune myocarditis (EAM) can be induced in the Lewis rat by cardiac myosin or its cryptic S2-16 peptide epitope (amino acids 1052 to 1076). To investigate cellular mechanisms and the role of antigen-presenting cells in regulation of myocarditis, we induced protection against EAM in Lewis rats by administration of S2-16 peptide in incomplete Freund's adjuvant (IFA). Protection to EAM was associated with activation of S2-16-reactive splenocytes secreting high levels of interleukin (IL)-10 and reduced levels of interferon-gamma and IL-2. Adoptive transfer of S2-16:IFA-induced splenocytes producing IL-10 suppressed myocarditis induction in syngeneic recipients, suggesting their regulatory cell nature. However, exposure of S2-16:IFA-induced cells to inflammatory cytokine IL-12 converted them to Th1 effectors that transferred EAM. Differentiated function of S2-16-reactive T cells in protected rats resulted from increased IL-10 production by dendritic cells (DCs). Purified DCs from S2-16:IFA-treated rats promoted S2-16-reactive CD4+ T cells to produce increased IL-10 and reduced interferon-gamma. In addition, adoptive transfer of IL-10-producing DCs from S2-16:IFA-treated rats also induced protection to EAM in recipient rats. These studies demonstrated DCs and key cytokines, such as IL-10 and IL-12, regulated the fate of T cells in myocarditis development in the Lewis rat.

Immune activation in chronic heart failure

In chronic heart failure (CHF), activation of the immune system occurs, which results in the production and release of proinflammatory cytokines, activation of the complement system, and production of autoantibodies. Thus, it is important to consider CHF as a systemic illness, not just a disease of the "pump." Immune activation in CHF can be divided into 2 broad categories: (1) immune activation by direct antigenic stimulation, or (2) immune activation secondary to cardiac injury that exposes "new antigens" capable of triggering an immune response against the heart. Cytokines are essential for the propagation and magnification of the immune response. They are involved in recruiting cells to the area of inflammation, stimulating cell division, proliferation, and differentiation. Circulating levels of the cytokine tumor necrosis factor-alpha (TNF-alpha) are increased in patients with CHF. Thus, cytokines are key elements of immune activation. Studies to investigate the role of increased TNF-alpha levels have failed to show a correlation with worsening CHF, most likely because the immune system is redundant, and other proinflammatory cytokines (interleukin [IL]-1 and IL-6) are known to be elevated in CHF. Approaches showing promise are those that enhance the natural anti-inflammatory response (eg, intravenous immunoglobulin (IVIG), immunoadsorption, immune-modulation therapy [IMT]), rather than those that specifically target a single type of cytokine. The mechanism by which IVIG modulates the immune system is unknown. Immunoadsorption involves the removal of specific antibodies from circulation. IMT works by inducing apoptosis in a sample of blood, which is then administered back to the patient. The immune system reacts by removing the apoptotic cells, thus inducing a systemic anti-inflammatory response.

Cryptic epitope identified in rat and human cardiac myosin S2 region induces myocarditis in the Lewis rat

Myocarditis is a common cause of dilated cardiomyopathy leading to heart failure. Chronic stages of myocarditis may be initiated by autoimmune responses to exposed cardiac Ags after myocyte damage. Cardiac myosin, a heart autoantigen, induced experimental autoimmune myocarditis (EAM) in susceptible animals. Although cardiac myosin-induced myocarditis has been reported in Lewis rats, the main pathogenic epitope has not been identified. Using overlapping synthetic peptides of the S2 region of human cardiac myosin, we identified an amino acid sequence, S2-16 (residues 1052-1076), that induced severe myocarditis in Lewis rats. The myocarditic epitope was localized to a truncated S2-16 peptide (residues 1052-1073), which contained a sequence identical in human and rat cardiac myosin. The S2-16 peptide was not myocarditic for three other strains of rats, in which the lack of myocarditis was accompanied by the absence of strong S2-16-specific lymphocyte responses in vitro. For Lewis rats, S2-16 was characterized as a cryptic epitope of cardiac myosin because it did not recall lymphocyte and Ab responses after immunization with cardiac myosin. Lymphocytes from S2-16 immunized rats recognized not only S2-16, but also peptides in the S2-28 region. Furthermore, peptide S2-28 was the dominant epitope recognized by T cells from cardiac myosin immunized rats. S2-16 was presented by Lewis rat MHC class II molecules, and myocarditis induction was associated with an up-regulation of inflammatory cytokine production. S2-16-induced EAM provides a defined animal model to investigate mechanisms of EAM and modulation of immune responses to prevent autoimmune myocarditis.