[Fibronectin--its functions and roles in tissue repair].

Fibronectin is a recently characterized 4.4 X 10(5) dalton glycoprotein consisting of two probably identical 2.2 X 10(5) dalton subunits held together by disulfide linkages. It is present as a soluble fraction in plasma at about 30mg/dl and is widely distributed as an insoluble component to various tissues, in close association with fibrillar structures of connective tissue matrices, basement membranes and certain mesenchymal cells including fibroblasts and smooth muscle cells. Fibronectin binds to fibrin and collagen reversibly and crosslinks to these filamentous proteins catalyzed by the activated blood coagulation factor XII (plasma transglutaminase). Plasma fibronectin appears to be utilized at the healing wounds, thus its concentration decreases during early postoperative days. Immunofluorescence study shows that fibronectin is closely associated with newly generated fibroblasts and fibrillar structures in the early stage of wound healing, and that it diminishes in accordance with the maturation of collagen fibers. Plasma fibronectin is shown to function to remove the colloidal debris from blood via the reticuloendothelial system and to play important roles in organizing the cytoskeleton and in the migration and spreading of interstitial cells. Thus fibronectin seems to play a pivotal role in the tissue repair via a variety of biological functions.