Shevach, Ethan M.

Abstract The immunopathogenesis of autoimmune myocarditis and dilated cardiomyopathy (DCM) in humans is unpredictable and pathogenic mechanisms undefined. The aim was to investigate potential autoimmune mechanisms in human autoimmune myocarditis and heart failure. Our evidence for a Th17 immunophenotype in human myocarditis/DCM(n=40) included reduced CD4+CD25+FoxP3+ Tregulatory cells(0.0006), elevated Th17 cells(0.0008) and increased Th17-promoting cytokines(IL-6 and TGF-beta). Th1(IFNγ+) cells were not significantly elevated(p=0.7184). IL-6(<0.0001), TGF-beta(0.0001), IL-23(0.0003), and GM-CSF+ T cells(0.0006) were significantly elevated. IL-17A+ cells were prevalent in biopsies from human myocarditis, non-recovery associated with persistence of IL-17A cytokines and heart failure associated with elevated Th17 cells in peripheral blood. To identify a potential mechanism to promote a Th17 pro-inflammatory pathogenesis in the heart, novel TLR ligands of human cardiac myosin (HCM) (peptides S2-16 and S2-28) promoted myocarditic PBMCs/CD14+ monocytes to produce Th17 cytokines(IL-23 p=0.0289; IL-6,TGF-beta p<0.0001). TLR ligand stimulation of PBMCs/ monocytes was abrogated by antibodies blocking TLR2, IL-6, IL-17A/23, and GM-CSF. Our translational study suggested human myocarditis/DCM may be controlled by a Th17 phenotype including reduced Treg, elevated Th17 cells, and pro-inflammatory and pro-fibrotic Th17 cytokines triggered by cardiac myosin TLR ligands potentially released from heart.

In human myocarditis and its sequela dilated cardiomyopathy (DCM), the mechanisms and immune phenotype governing disease and subsequent heart failure are not known. Here, we identified a Th17 cell immunophenotype of human myocarditis/DCM with elevated CD4 + IL17 + T cells and Th17-promoting cytokines IL-6, TGF-β, and IL-23 as well as GM-CSF–secreting CD4 + T cells. The Th17 phenotype was linked with the effects of cardiac myosin on CD14 + monocytes, TLR2, and heart failure. Persistent heart failure was associated with high percentages of IL-17–producing T cells and IL-17–promoting cytokines, and the myocarditis/DCM phenotype included significantly low percentages of FOXP3 + Tregs, which may contribute to disease severity. We demonstrate a potentially novel mechanism in human myocarditis/DCM in which TLR2 peptide ligands from human cardiac myosin stimulated exaggerated Th17-related cytokines including TGF-β, IL-6, and IL-23 from myocarditic CD14 + monocytes in vitro, and an anti-TLR2 antibody abrogated the cytokine response. Our translational study explains how an immune phenotype may be initiated by cardiac myosin TLR ligand stimulation of monocytes to generate Th17-promoting cytokines and development of pathogenic Th17 cells in human myocarditis and heart failure, and provides a rationale for targeting IL-17A as a therapeutic option.