LECTIN-BINDING IN THE ANTERIOR SEGMENT OF THE BOVINE EYE

Eleven different fluorescent lectin-conjugates were used to reveal the location of carbohydrate residues in frozen sections of the anterior segment of bovine eyes. The lectins were specific for the following fi ve major carbohydrate groups: (1) glucose/mannose group (Concanavalin A (Con A)); (2) N-acetylglucosamine group (wheat germ agglutinin (WGA) ); (3) galactose/N-acetylgalactosamine group (Dolichos biflorus agglut inin (DBA), Helix pomatia agglutinin (HPA), Helix aspersa agglutinin ( HAA), Psophocarpus tetragonolobus agglutinin (PTA), Griffonia simplici folia agglutinin-I-B-4; (GSA-I-B-4), Artocarpus integrifolia agglutini n (JAC), peanut agglutinin (PNA) and Ricinus communis agglutinin (RCA- I)); (4) L-fucose group (Ulex europaeus agglutinin (UEA-I)); (5) siali c acid group (wheat germ agglutinin (WGA)). All the studied lectins ex cept UEA-I reacted widely with different structures and the results su ggest that there are distinct patterns of expression of carbohydrate r esidues in the anterior segment of the bovine eye. UEA-I bound only to epithelial structures. Some of the lectins reacted very intensely wit h apical cell surfaces of conjunctival and corneal epithelia suggestin g a different glycosylation at the glycocalyx of the epithelia. Also, the binding patterns of conjunctival and corneal epithelia differed wi th some of the lectins: PNA and RCA-I did not bind at all, and GSA-I-B -4 bound only very weakly to the epithelium of the cornea, whereas the y bound to the epithelium of the conjunctiva. In addition, HPA, HAA, P NA and WGA did not bind to the corneal basement membrane, but bound to the conjunctiva and vascular basement membranes. This suggests that c orneal basement membrane is somehow different from other basement memb ranes. Lectins with the same carbohydrate specificity (DBA, HPA, HAA a nd PTA) reacted with the sections almost identically, but some differe nces were noticed: DBA did not bind to the basement membrane of the co njunctiva and the sclera and did bind to the basement membrane of the cornea, whereas other lectins with same carbohydrate specificities rea cted vice versa. Also, the binding of PTA to the trabecular meshwork w as negligible, whereas other lectins with the same carbohydrate specif icities reacted with the trabecular meshwork. GSA-I-B-4 reacted avidly with the endothelium of blood vessels and did not bind to the stroma, so that it made blood vessels very prominent and it might be used as an endothelial marker. This lectin also reacted avidly with the cornea l endothelium. Therefore, GSA-I-B-4 appears to be a specific marker in bovine tissues for both blood vessel and corneal endothelium cells.