Role of myofibroblasts in pseudointima formation.

Twenty Dacron grafts (10 crimped and 10 noncrimped) were studied with light microscopy, scanning electron microscopy, and transmission electron microscopy (TEM) 1 to 10 months after insertion into the canine thoracoabdominal aorta. Fibroblast-derived pseudointima maintained a smooth luminal lining that approximated the luminal cross-sectional area of the aorta. Turbulent flow at the corrugated surface of crimped grafts was reflected by the nonuniform alignment of the luminal cells. TEM demonstrated that fibroblasts, macrophages, vasa, and nerve fibers had infiltrated the interstices of the grafts. A zone of loose connective tissues and ground substances existed between the graft surface and the pseudointima and occupied the zone between the luminal cells and the body of the pseudointima. The core of the pseudointima consisted of dense fibrous connective tissue elements and myofibroblasts arranged in a laminated pattern. The luminal cells that were seen were myofibroblasts containing microvilli rather than true endothelial cells. A gradual transition of fibroblast to myofibroblast from the graft to the lumen existed. Myofibroblasts with active rough endoplasmic reticula and Golgi complexes were responsible for formation of ground substances and extracellular matrix. Our observation strongly suggests that the cellular lining in healed Dacron prostheses is derived from modified fibroblasts or multipotential cells. These cells have the capability of transforming into endothelioid and myoblastoid cells as dictated by the functional need.