3A and B). Interestingly, at the age of 12 weeks, heart parameters as determined by CMRI were normalized in the recruited cohort (Table 1). Likewise, left ventricle wall thickness had normalized again (Fig. 3B), despite persisting histopathological signs of myocarditis (Fig. 3C), suggestingthat the hearts from these TCR-M mice had successfully compensated the early alterations in heart muscle function.

Taken together, this analysis shows that the TCR-M model is well suited to monitor the pathophysiological changes see more in the heart muscle during the initiation of cardiac inflammatory disease and to characterize the parameters of successful heart muscle remodeling in chronic myocarditis. Next, we analyzed the CD4+ T-cell activation and differentiation patterns in AZD4547 clinical trial TCR-M mice. Assessment of CD62L downregulation on CD4+ T cells revealed significant accumulation of activated T cells in the heart-draining LN and in inflamed hearts of TCR-M mice (Fig. 4A). Interestingly, Foxp3 expression in spleen and heart-draining LNs of TCR-M mice was not significantly different from controls, and a high proportion of the heart-infiltrating CD4+ T cells expressed Foxp3 (Fig. 4B), indicating that

the presence of regulatory T cells both in secondary lymphoid organs and the heart was not sufficient to prevent spontaneous and severe myocarditis in TCR-M mice. Isolation of heart-infiltrating CD4+ T cells and stimulation with myhca614–629 peptide or PMA/ionomycin revealed that IFN-γ and IL-17 were the dominant cytokines produced enough by the TCR-transgenic T cells (Fig. 4C). Interestingly, the highest production of IFN-γ following peptide restimulation was observed in hearts

from 4 weeks old TCR-M mice, whereas IL-17 production of heart-infiltrating TCR-transgenic CD4+ T cells did not significantly change during the course of the disease (Fig. 4C). Furthermore, heart-infiltrating CD4+ T cells produced TNF-α and IL-2, although to a lesser extent, and did not show production of IL-4 or IL-10 (data not shown) indicating that myhca-specific CD4+ T cells in TCR-M hearts were biased towards a Th1/Th17 phenotype. Since these cytokines exert potent effects on myeloid cells during different autoimmune diseases [27] including autoimmune myocarditis [28], we assessed the recruitment of myeloid cells into the inflamed heart of TCR-M mice. As shown in Supporting Information Fig. 5, both macrophages and DCs formed major fractions of the heart-infiltrating cells. To assess the impact of the Th1 and Th17 signature cytokines on the pathogenesis of myocarditis and in the propagation to fatal DCM, we crossed TCR-M mice onto the IL-17A- and IFNGR-deficient backgrounds. IFNGR-deficient mice were preferred here over IFN-γ-deficient animals because we considered assessment of IFN-γ production as important for the overall evaluation of the cytokine effects on the disease development. As shown in Fig.