Human amniotic membrane, like corneal epithelial basement membrane, manifests the alpha5 chain of type IV collagen

PURPOSE: To reexamine whether the alpha5 chain of type IV (alpha5[IV]) collagen, thought to be absent, is in fact present in human amniotic membrane. METHODS: Cryosections of human amniotic membrane obtained at Cesarean section were immunohistochemically examined for the presence of alpha5(IV), with or without inclusion of the denaturing step. Amniotic membrane was digested with collagenase to release the noncollagenous NC1 domain from the alpha-chain. The NC1 domain of alpha5(IV) was then assayed on Western blot analysis. Identical experiments were performed with human corneas and conjunctivae obtained from an American eye bank. RESULTS: The basement membrane of denatured samples of amniotic membrane and cornea stained positive for alpha5(IV). Without the denaturing step, only corneal samples were positive. With or without denaturing, conjunctival epithelium did not stain. Western blot analysis detected NC1 domains of alpha5(IV) in amniotic membrane and corneal samples. CONCLUSIONS: The basement membrane of amniotic membrane resembles that of corneal epithelium but not conjunctiva. Amniotic membrane may be an excellent substrate for corneal epithelial cells.