The immunohistochemical composition of the human corneal basement membrane

Frozen sections of human cornea and conjunctiva were stained by immunofluorescence and immunoperoxidase methods with a panel of antibodies against various basement membrane (BM) and extracellular matrix proteins to study the composition of the human corneal BM. Laminin (Ln) immunoreactivity was detected in the BMs of the blood vessels and conjunctival, limbal, and corneal epithelia by using a polyclonal antiserum and monoclonal antibodies (MAbs) against Ln chains alpha 1, beta 1, and gamma 1, but in the cornea the reaction with MAbs against alpha 1, beta 1, and gamma 1 chains was clearly weaker than in the other BMs and in some sections totally absent. Immunoreactivity to Ln alpha 2 chain was detected only in the BM of the limbus, whereas Ln beta 2 chain was detected in the BMs of blood vessels and that of conjunctival and limbal epithelia. Ln-5 and Ln alpha 3 and beta 3 chains were seen in the BMs of the corneal, limbal, and conjunctival epithelia coaligning the integrin beta 4. Immunoreactivity for collagen type IV was lacking in the BM of the corneal epithelium, but present in the BMs of the limbal and conjunctival epithelia as well as in the vascular BM. Collagen type VII immunoreactivity was seen in the BM areas of the corneal, limbal, and conjunctival epithelia. BMs of corneal, limbal, conjunctival, and vascular epithelia expressed fibronectin (Fn), including extradomain A cellular Fn and oncofetal cellular Fn isoforms, all lacking, however, extradomain B cellular Fn. The present results give new information on the Ln chain distribution and show that the BM of the corneal epithelium differs from that of surrounding epithelia by the lack of collagen type IV.