Myosin-induced acute myocarditis is a T cell-mediated disease

The heart is a target organ in several autoimmune diseases, and therefore it is important to understand more about the effector cells involved in immune-mediated mechanisms of myocardial cell death. Because immune T lymphocytes are central to many immune responses, we wanted to study the role of T cells in causing cardiac specific inflammation. We used purified mouse cardiac myosin to cause acute myocarditis in mice. The adoptive transfer of purified T cells from C.B-17 mice with active myocarditis to SCID recipients successfully transferred the disease into SCID hosts. In contrast, transfer of serum with high-titer antimyosin antibodies to SCID hosts did not cause myocarditis. Using mAb to deplete A/J mice of CD4⁺ T cells, we showed that these mice were protected against the induction of myocarditis. Depletion of CD8⁺ T cells reduced the severity of inflammation but did not prevent induction of myocarditis. We were also able to prevent the induction of myocarditis using major histocompatibility class II protein-binding, nonimmunogenic, competitor peptides. These blocking studies also indicated that in H-2^k mice, myocarditis is an I-A^k-restricted disease, and provided further evidence that CD4⁺ T cells are critical to the induction of disease. Together, these studies provide direct evidence that myosin-induced myocarditis is a T cell-mediated disease.