BackgroundTumor necrosis factor-α (TNF-α) has been reported to have an antiviral effect in vitro; however, its in vivo effect remains to be clarified.Methods and ResultsTo investigate the role of TNF-α in viral myocarditis using a murine model induced by encephalomyocarditis virus (EMCV), we evaluated (1) plasma TNF-α levels by enzyme-linked immunosorbent assay (ELISA), (2) the effect of recombinant human TNF-α for its possible antiviral effect in vivo, and (3) the effect of anti-murine TNF-α monoclonal antibody (mAb) in vivo. Four-week-old DBA/2 mice were inoculated intraperitoneally with EMCV (day 0). Mice were injected intravenously daily with 1,μg of TNF-α or 2×103units of anti–TNF-α mAb starting on day -1, day 0, or day 1 until day 2 (TNF-α study) or day 4 (anti-TNF-α mAb study). A portion of the mice were killed on day 5 (protocol 1); their hearts were removed, and plaque assays were performed to demonstrate the myocardial virus content. The remaining mice were killed on day 14 (protocol 2); myocardial lesions were examined histopathologically in terms of severity, and their survival rates were determined. Plasma TNF-α concentration was elevated in the blood of infected mice compared with uninfected mice 3, 5, and 7 days after virus inoculation. The myocardial virus content was higher in the TNF-α–treated group than in the control group. Histopathological analysis revealed that myocardial necrosis and cellular infiltration were more prominent in the TNF-α group than in the control group. The anti-TNF-α mAb improved survival and myocardial lesions when its treatment was started 1 day before virus inoculation. However, it showed no therapeutic effect when administered simultaneously with the inoculation or on day 1.ConclusionsTNF-α may play an important role in the very early stage of the immune response, and anti-TNF-α mAb may prevent the early pathway of acute viral myocarditis.