Vitronectin (Vn) is a multifunctional plasma
glycoprotein produced by hepatocytes. Vn has been studied extensively as a
cell adhesion molecule. However, its localization in the hepatic extracellular matrix has received relatively little attention. Cryosections of 5 normal liver samples and of 20 specimens showing posthepatitic
cirrhosis were stained by the
avidin-
biotin complex method with a well-characterized
monoclonal antibody to Vn. The extent and intensity of immunostaining were assessed semiquantitatively (0, no staining; 1+, weak focal staining; 2+, strong focal staining; 3+, strong diffuse staining).
Paraffin sections from the same samples were stained with Masson trichrome (MT) and Shikata
orcein (Or) methods. Frozen samples from selected cases were analyzed by Western blotting. In the normal liver, 3+ staining was limited to portal vessels. The portal tract connective tissue showed minimal staining (0 to 1+). Cirrhotic septa showed strong staining (2+). Septa lacking significant
inflammation and composed of dense connective tissue, as indicated by MT and Or stains, showed the strongest Vn reactions (3+). Immunoblotting data strongly correlated with Vn increase in cirrhotic livers. Vn immunoreactivity is markedly increased in the cirrhotic liver matrix, regardless of the documented decrease in plasma Vn. Binding to
collagen,
elastin, and
proteoglycans is the current favored mechanism of Vn deposition in tissues. Previous studies in cirrhotic patients showed increased affinity of plasma Vn to
collagen. Vn is also increased in aged skin, associated with dermal elastic fibers. In other tissues, Vn deposition reflects chronicity of injury. Therefore, Vn immunoreactivity in liver can be considered a marker of
fibrosis, especially of chronic/mature
fibrosis, paralleling previous observations on enhanced
orcein staining of cirrhotic septa. Immunolabeling of biopsy specimens with Vn and
tenascin, a marker of ongoing remodeling or recently formed fibrous tissue, could be diagnostically helpful.