Fibronectin in the lung

Reviews of the structure and function of the fibronectins are given elsewhere in this volume. This chapter will provide an overview of fibronectin in the lung. Fibronectin functions in the lung in three separate, interacting compartments: the pulmonary parenchymal interstitium, the intravascular space of the pulmonary vascular bed, and the epithelial surface lining the airspaces of the lung. By virtue of its multiple binding sites, fibronectin can mediate a variety of interactions between cells and components of the extracellular milieu. As in other organs, a variety of roles have been suggested for fibronectin in the pulmonary parenchyma including the organization of extracellular matrix and the regulation of cellular recruitment, proliferation and differentiation both during normal development and during repair processes following injury. Fibronectin present in the vascular lumen, by virtue of its activity as an opsonin, protects the lung from microembolic injury. In addition, plasma fibronectin may be an important determinant of lung vascular membrane integrity, particularly at times of stress. Fibronectin present on the epithelial surface of the lung appears to aid in host defense against bacterial infection. Fibronectin, therefore, is likely involved in a number of diverse pathologic conditions affecting the lung.