Therapeutic implications of immune mechanisms in myocarditis

Myocarditis and idiopathic dilated cardiomyopathy

Idiopathic dilated cardiomyopathy (IDC) accounts for 25% of cases of heart failure in the United States. Understanding the relationship between an inciting event or agent and the development of IDC has progressed only recently. Once IDC has developed, treatment is palliative and little can be done to alter the natural course of the disease. Active myocarditis, a suspected precursor of IDC, is myocardial inflammation and injury without ischemia. The disease ranges from a self-limited flulike illness to one of serious consequence with arrhythmias, heart failure, or death. Many agents have been associated with myocarditis, and the clinical manifestations depend on an interplay between the inciting agent and the host response. The development of a murine model and the expanded use of endomyocardial biopsy using the Dallas criteria have increased our understanding of myocarditis and its sequelae. Therapy consists of managing symptoms using conventional medical regimens for heart failure. Immunosuppressive therapy should be reserved for patients with biopsy-proven disease who have failed conventional therapy. Continued deterioration warrants ventricular assistance and consideration of cardiac transplantation.

Effect of immunostimulant therapy on acute viral myocarditis in an animal model

The effect of immunostimulant therapy on acute viral myocarditis, which was induced with encephalomyocarditis virus, was investigated in 4-week-old male BALB/c mice. In vitro, peritoneal exudate cells and spleen cells from mice that were pretreated with a synthetic immunoactivating peptide, FK565 (heptanoyl-gamma-D-glutamyl-(L)-meso-diaminopimelyl-(D)-alan ine), significantly inhibited the multiplication of encephalomyocarditis virus in BALB/c 3T3 cells compared with peritoneal exudate cells and spleen cells from untreated mice (6.14 +/- 0.21 log10 plaque-forming units (pfu) per milliliter, control: 6.59 +/- 0.03, p less than 0.05; 3.55 +/- 0.23, control: 5.64 +/- 0.09, p less than 0.01, respectively), although FK565 did not inhibit viral replication directly. The mice were inoculated intraperitoneally with 100 pfu of encephalomyocarditis virus. FK565 (1 mg/kg/day), which was administered 1 day before or simultaneously with virus inoculation, effectively inhibited myocardial viral replication (2.77 +/- 0.17 log10 pfu/mg, 2.46 +/- 0.35, log10 pfu/mg, respectively, control: 3.33 +/- 0.26, p less than 0.025) and increased survival (70% and 60%, respectively, control: 20%, p less than 0.01). Histopathologic findings were scored on a scale of 0 to 4. Treatment with 1 mg/kg/day of FK565 that was started 1 day before virus inoculation was most effective in reducing the inflammatory response (1.2 +/- 0.63, control: 2.0 +/- 0.81, p less than 0.05) and myocardial necrosis (1.2 +/- 0.42, control: 2.0 +/- 1.00, p less than 0.025). The present study suggests that immunostimulant therapy improves the course of viral myocarditis during the virus-mediated phase.(ABSTRACT TRUNCATED AT 250 WORDS)