Abstract
Acanthamoeba keratitis is a vision-threatening corneal infection. The mannose-binding protein of Acanthamoeba is thought to mediate adhesion of parasites to host cells. We characterized the amoeba lectin with respect to its carbohydrate binding properties and the role in amoeba-induced cytopathic effect (CPE). Sugar inhibition assays revealed that the amoeba lectin has the highest affinity for alpha-Man and Man(alpha1-3)Man units. In vitro cytopathic assays indicated that mannose-based saccharides which inhibit amoeba adhesion to corneal epithelial cells were also potent inhibitors of amoeba-induced CPE. Another major finding was that N-acetyl-D-glucosamine (GlcNAc) which does not inhibit adhesion of amoeba to host cells is also an inhibitor of amoeba-induced CPE. The Acanthamoebae are thought to produce CPE by secreting cytotoxic proteinases. By zymography, one metalloproteinase and three serine proteinases were detected in the conditioned media obtained after incubating amoebae with the host cells. The addition of free alpha-Man and GlcNAc to the co-culture media inhibited the secretion of the metalloproteinase and serine proteinases, respectively. In summary, we have shown that the lectin-mediated adhesion of the Acanthamoeba to host cells is a prerequisite for the amoeba-induced cytolysis of target cells and have implicated a contact-dependent metalloproteinase in the cytopathogenic mechanisms of Acanthamoeba.
Highlights
Acanthamoeba keratitis is a painful, vision-threatening corneal infection
It is believed that minor corneal surface injury caused by contact lens wear or other noxious agents and exposure to contaminated solutions, including lens care products and tap water, are two major factors in the pathogenesis of the keratitis
We show that the Acanthamoeba lectin binds ␣-Man and ␣1–3-D-mannobiose with highest affinity and that the lectinmediated adhesion of the amoeba to host cells is a prerequisite for the amoeba-induced cytolysis of target cells
Summary
Acanthamoeba keratitis is a painful, vision-threatening corneal infection. It is caused by parasites of the genus Acanthamoeba [1, 2]. It is believed that minor corneal surface injury caused by contact lens wear or other noxious agents and exposure to contaminated solutions, including lens care products and tap water, are two major factors in the pathogenesis of the keratitis. The adhesion of the parasite to the host cells is thought to be a critical first step in the pathogenesis of infection [3,4,5]. We show that the Acanthamoeba lectin binds ␣-Man and ␣1–3-D-mannobiose with highest affinity and that the lectinmediated adhesion of the amoeba to host cells is a prerequisite for the amoeba-induced cytolysis of target cells
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