Matrix metalloproteinases in the pathogenesis of viral heart disease.

Matrix metalloproteinases (MMPs) are enzymes that digest the extracellular matrix and regulate the immune response by cleavage of chemokines and cytokines into products with altered activities. Matrix metalloproteinase expression in viral heart disease has been linked to the onset of myocarditis and the long-term sequelae associated with this illness. However, MMPs are also expressed as a functional part of the immune response, and it was recently shown that MMP-9 is a beneficial part of the antiviral immune response in viral myocarditis. In this review, we will attempt to reconcile the studies that claim MMPs inflict damage in viral myocarditis with those studies that report a protective role for MMPs in this cardiac disease.