Immunolocalization of entactin, a sulfated basement membrane component, in rodent tissues, and comparison with GP-2 (laminin).

Entactin is a sulfated glycoprotein in the extracellular basement membrane like matrix produced by M1536-B3 cells, a mouse endodermal line derived from an embryonal carcinoma. It has a molecular weight of 158,000 and is chemically and immunologically distinguishable from GP-2 (laminin) and fibronectin. Antibodies produced against entactin and GP-2 react with subepithelial and vascular basement membranes in rat lung, liver, spleen, and kidney and mouse placenta and kidney when examined by light microscopy. Both antibodies yield staining around the marginal sinus of the white pulp of the spleen. Antientactin reacts with basement membrane and mesangium in rat glomeruli, and anti-GP2 does not. Ultrastructurally, staining in kidneys is strongest at epithelial or endothelial cell membranes bordering basement membranes, with only moderate staining of the basement membrane proper. Intracellular staining is not present. The location of entactin suggests that it has a role in the interaction of cells with extracellular matrix, possibly in adhesion. Lack of intracellular staining suggests that the tissues studied are not actively producing entactin or GP-2 and that these substances may be fairly stable in adult organisms.