T cells in acute and chronic myocarditis: from diagnosis to treatment

Myocarditis refers to infiltration of immune cells into the heart causing inflammation and cardiomyocyte damage. Clinically, myocarditis can be acute or chronic. While the clinical and pathological syndrome of myocarditis has been recognized for more than a century, newer aetiologies for myocarditis have emerged in the past decade. These include myocarditis associated with immune checkpoint inhibitors, or myocarditis linked to chronic inflammatory and genetic diseases. With the emergence of immune checkpoint inhibitor-associated myocarditis, the breakdown of T cell tolerance has been recognized as a key mechanism in disease development. The main focus of this review is to integrate existing models of myocarditis into an overarching immunological concept. Through the lens of loss of immune tolerance, this review focuses on diagnosis and treatment of myocarditis. Starting from acute myocarditis as paradigmatic inflammatory condition of the heart, this review outlines future research frontiers for myocardial inflammatory disease including new approaches to diagnosis and treatment.