Potential role of the adventitia in arteritis and atherosclerosis.

The role of the adventitia in vascular lesion formation has been largely ignored despite numerous studies which have suggested its potential importance. Adventitial reactions are common in atherosclerosis as well as arteritis. Experimental hypercholesterolemia in pigs and non-human primates stimulates the accumulation of inflammatory cells in the arterial adventitia. The extent of adventitial inflammation associated with human atherosclerotic plaques is correlated with the severity of intimal disease. Adventitial reactions also occur after balloon angioplasty. Our studies indicate that the major site of cell proliferation after angioplasty of porcine coronary arteries is the adventitia and not the medial wall. These cells have been identified as myofibroblasts on the basis of differential staining with smooth muscle specific antibodies and a role for these cells in arterial remodeling associated with angioplasty and late lumen loss is postulated. Evidence from pulse studies with bromodeoxyuridine suggests that adventitial myofibroblasts have the capacity to migrate into the forming intimal lesion after angioplasty and may be a major component of the neointima. Additional work will have to be directed at a more detailed examination of the response of adventitial cells to balloon injury and in the setting of atherosclerosis and arteritis to determine what role these cells might play vascular lesion development.