Cooperation of Th1 and Th17 cells determines transition from autoimmune myocarditis to dilated cardiomyopathy.

Myocarditis is a potentially lethal inflammatory heart disease of children and young adults that frequently leads to dilated cardiomyopathy (DCM). Since diagnostic procedures and efficient therapies are lacking, it is important to characterize the critical immune effector pathways underlying the initial cardiac inflammation and the transition from myocarditis to DCM. We describe here a T-cell receptor (TCR) transgenic mouse model with spontaneously developing autoimmune myocarditis that progresses to lethal DCM. Cardiac magnetic resonance imaging revealed early inflammation-associated changes in the ventricle wall including transient thickening of the left ventricle wall. Furthermore, we found that IFN-γ was a major effector cytokine driving the initial inflammatory process and that the cooperation of IFN-γ and IL-17A was essential for the development of the progressive disease. This novel TCR transgenic mouse model permits the identification of the central pathophysiological and immunological processes involved in the transition from autoimmune myocarditis to DCM.

Molecular mapping of autoimmune B cell responses in experimental myocarditis.

Autoimmune responses directed against heart-specific antigens most likely play a key role in the pathogenesis of myocarditis. Although autoantibodies against cardiac determinants are frequently detected both in human patients and mice suffering from myocarditis, the immunological mechanisms for their induction have not yet been fully explored. We used here the SEREX approach (serological identification of recombinantly expressed proteins) to molecularly dissect heart-specific autoimmune B cell responses that develop in the course of experimentally induced myocarditis. Screening of a heart cDNA library with sera of cardiac myosin heavy chain alpha (myhcalpha) peptide-immunized BALB/c mice revealed a strong focusing of the B cell response on the myhcalpha protein. The vast majority of the myhcalpha transcripts coded for regions other than the sequence of the immunogenic myhcalpha peptide, indicating extensive intramolecular epitope spreading. Importantly, we found that the infection with cardiotropic viruses such as MCMV and Coxsackievirus B3 elicited specific autoantibody pattern with a particular skewing to the myhcalpha protein. The induction of myhcalpha peptide-specific Th cells in the course of both infections suggests that infection-associated determinant spreading on the Th cell level paves the way for a focused and dominant anti-myhcalpha B cell response.

Quantification and characterization of myosin peptide-specific CD4+ T cells in autoimmune myocarditis.

Characterization of autoantigen-specific CD4+ T cells at the single cell level is crucial for understanding the immunopathological mechanisms underlying autoimmune diseases. Cardiac myosin heavy chain (myhca) is the major autoantigen associated with autoimmune myocarditis both in humans and in experimental autoimmune myocarditis (EAM) in mice. In the current study, we evaluated two methods for the enumeration and phenotypic characterization of myhca-specific CD4+ T cells during the course of EAM. Both enzyme-linked immunospot (ELISPOT) and cytokine flow cytometry (CFC) assays were suitable for the detection and characterization of myhca-specific Th cells during acute myocardial inflammation and the late healing phase of the disease. Cytokine production of myhca-specific Th cells was restricted to interferon-gamma (IFNgamma). Only trace amounts of the Th2 cytokines IL-4 and IL-5 could be detected. Concomitant surface marker analysis in the CFC assay revealed the prototypical effector phenotype of myhca-specific Th1 cells during the acute phase of the disease. Taken together, the combination of both methods appears to be most appropriate for a comprehensive ex vivo single cell analysis of Th cells in heart-specific autoimmune disorders.