PATHOGENESIS OF ACANTHAMOEBA-KERATITIS - CARBOHYDRATE-MEDIATED HOST-PARASITE INTERACTIONS

Acanthamoeba keratitis is a sight-threatening corneal infection. In a recent study, the saccharide mannose has been shown to inhibit the bin ding of Acanthamoeba organisms to the epithelium of the cornea (L. D, Morton, G, L. McLaughlin, and H. E, Whiteley, Infect, Immun. 59:3819-3 822, 1991). In an attempt to determine the molecular mechanism by whic h acanthamoebae adhere to the surface of the cornea, the present study was designed to determine whether Acanthamoeba castellanii derived fr om an infected human cornea (i) binds to mannose-containing glycoprote ins (mannose-GPs) of corneal epithelium and (ii) expresses one or more mannose-binding proteins, Mannose-GPs of primary cell cultures of rab bit corneal epithelium were isolated by using three different agarose- conjugated, mannose-specific lectins, By electrophoresis blot-overlay assays, S-35-labeled acanthamoebae were shown to bind to mannose-GPs o f corneal epithelium and to a neoglycoprotein, mannose-bovine serum al bumin (mannose-BSA), S-35-labeled acanthamoebae also bound to microtit er wells coated with mannose-BSA in a concentration-dependent manner. The binding of amoebae to mannose-GPs was blocked by free methyl-alpha -D-mannopyranoside. The parasites did not bind to galactose-BSA or to many other proteins lacking mannose residues, A membrane-associated ma nnose-binding protein (136 kDa) of A, castellanii was isolated by affi nity chromatography of detergent extracts of unlabeled parasites and o f cell surface biotin-labeled parasites on a rho-aminophenyl alpha-D-m annopyranoside-agarose column. The affinity purified protein of the am oeba was shown to bind specifically to mannose-BSA, In summary, a mann ose-binding protein is present on the surface membranes of Acanthamoeb a, and corneal epithelial cells express Acanthamoeba reactive GPs. One of the mechanisms of Acanthamoeba adhesion to the corneal surface may involve interactions between the mannose-binding protein of Acanthamo eba and mannose-GPs on the surface of corneal epithelium.