To elucidate the mechanisms of immune-related myocardial injuries, we examined whether autoimmune myocarditis was passively transferable by use of humoral or cellular factors.

Active myocarditis was elicited in Lewis rats by immunization with human cardiac myosin fraction in complete Freund's adjuvant. This experimental myocarditis was characterized by macroscopic features such as pericardial effusion, enlargement of the heart, and gray discoloration of the cardiac surface. Histologically, extensive myocardial necrosis and numerous inflammatory cell infiltrations were observed. Interestingly, multinucleated giant cells were frequently observed in the lesions. Transfer of the disease by the humoral factor was examined by use of fresh sera and immunoglobulin fraction of pooled sera from rats with severe myocarditis, and transfer by the cellular factor was tested by use of spleen cells and lymph node cells from the diseased rats. When naive Lewis rats were given 15.75 mg of immunoglobulin fraction, no particular change was observed in the hearts. Fresh sera also could not elicit myocarditis in recipient rats. In contrast, intravenous injection of spleen cells or lymph node cells that were cultured for 3 days in the presence of 1 microgram/ml of concanavalin A elicited severe myocarditis. The macroscopic and microscopic findings of passively transferred myocarditis are essentially the same as those found in actively induced myocarditis. Multinucleated giant cells were also observed in the lesions of transferred myocarditis.

This study demonstrates direct evidence for in vivo lymphocyte-mediated myocardial injuries.