A pathogenic mechanism of chronic ongoing myocarditis

To clarify the pathogenetic mechanism of chronic ongoing myocarditis, we produced Coxsackievirus B3-induced myocarditis in A/J mice and immunopathologically examined the microcirculation in the chronic phase of myocarditis. Forty-two 3-week-old A/J mice were inoculated intraperitoneally with Coxsackievirus B3 (Nancy strain) 2 x 10(4) PFU (plaque-forming units) and sacrificed 7, 14, 21, 50, 90, or 120 days later. To evaluate myocardial microcirculation, 18 of the hearts were perfused from the thoracic aorta with warm 2% gelatin/carbon solution. The remaining hearts were quickly frozen for immunologic analysis with an enzyme immunostaining assay using monoclonal antibodies against CD4, CD8, macrophages, intercellular adhesion molecule-1 (ICAM-1) and major histocompatibility complex class I or II. The presence of viral RNA genome in the myocardium at 40, 50, or 60 days after inoculation was evaluated using the polymerase chain reaction. The lesions in chronic ongoing myocarditis consisted of myocardial damage, myocardial calcification, interstitial fibrosis, and infiltration of mononuclear cells. These infiltrated lymphocytes were predominantly CD4+ T cells. Furthermore, microvascular abnormalities, including dilatation, tortuosity, constriction, and abrupt termination, were observed around the lesions. There was marked infiltration by mononuclear cells around the microvessels. ICAM-1 was strongly expressed in the endothelial cells of the vessels. Coxsackie B3 viral genome was not detected in the myocardium of mice with chronic ongoing myocarditis in each stage examined. These results suggest that an autoimmune mechanism is involved in the persistent inflammation seen in chronic ongoing myocarditis.