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Infect. Immun., Feb 1997, 439-445, Vol 65, No. 2
Z Yang, Z Cao and N Panjwani
Acanthamoeba keratitis is a sight-threatening corneal infection. In a
recent study, the saccharide mannose has been shown to inhibit the binding
of Acanthamoeba organisms to the epithelium of the cornea (L. D. Morton, G.
L. McLaughlin, and H. E. Whiteley, Infect. Immun. 59:3819- 3822, 1991). In
an attempt to determine the molecular mechanism by which acanthamoebae
adhere to the surface of the cornea, the present study was designed to
determine whether Acanthamoeba castellanii derived from an infected human
cornea (i) binds to mannose-containing glycoproteins (mannose-GPs) of
corneal epithelium and (ii) expresses one or more mannose-binding proteins.
Mannose-GPs of primary cell cultures of rabbit corneal epithelium were
isolated by using three different agarose-conjugated, mannose-specific
lectins. By electrophoresis blot-overlay assays, 35S-labeled acanthamoebae
were shown to bind to mannose-GPs of corneal epithelium and to a
neoglycoprotein, mannose-bovine serum albumin (mannose-BSA). 35S- labeled
acanthamoebae also bound to microtiter 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 mannose-binding protein (136 kDa) of A. castellanii was
isolated by affinity chromatography of detergent extracts of unlabeled
parasites and of cell surface biotin- labeled parasites on a p-aminophenyl
alpha-D-mannopyranoside-agarose column. The affinity-purified protein of
the amoeba was shown to bind specifically to mannose-BSA. In summary, a
mannose-binding protein is present on the surface membranes of
Acanthamoeba, 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
Acanthamoeba and mannose-GPs on the surface of corneal epithelium.
Copyright © 1997, American Society for Microbiology
Pathogenesis of Acanthamoeba keratitis: carbohydrate-mediated host- parasite interactions
The New England Eye Center, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
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