Myocardial uptake of antimyosin monoclonal antibody in a murine model of viral myocarditis.

The myocardial uptake of 125I- and 131I-antimyosin monoclonal antibody Fab in experimental myocarditis in BALB/c mice induced by encephalomyocarditis virus was studied. The biodistribution of 125I-antimyosin demonstrated that the highest ratio of radioactivity appears in the heart of infected mice on day 14 (the ratio of percent dose per gram for the organ to percent dose per milliliter for blood; 9.75 +/- 2.79 vs. 1.27 +/- 0.78 at 24 hours in inoculated mice vs. control mice). There was no statistically significant difference between the mean activity ratios of tissues other than the heart in control and inoculated mice. The uptake ratio for the heart increased significantly 3 days after virus inoculation and reached a maximum on day 14 when myocardial lesions were most extensive and prominent. The uptake ratio decreased significantly, but it still remained high compared with controls on day 28 when cellular infiltration had decreased and fibrosis was evident. The scintigraphic images obtained with 131I-antimyosin monoclonal antibody clearly demonstrated that visualization of the heart in experimental myocarditis was possible 24 hours after administration of radiotracer, and localized activity was still observed in the 48-hour image. We conclude that antimyosin monoclonal antibodies localize selectively in the heart from the acute to subacute stage of viral myocarditis. These findings indicate that antimyosin scintigraphy is a reliable noninvasive method for the evaluation of patients suspected of having myocarditis.