ROLE OF CARBOHYDRATE-MEDIATED ADHERENCE IN CYTOPATHOGENIC MECHANISMS OF ACANTHAMOEBA

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 r espect to its carbohydrate binding properties and the role in amoeba-i nduced cytopathic effect (CPE), Sugar inhibition assays revealed that the amoeba lectin has the highest affinity for alpha-Man and Man(alpha 1-3)Man units. In vitro cytopathic assays indicated that mannose-base d saccharides which inhibit amoeba adhesion to corneal epithelial cell s were also potent inhibitors of amoeba-induced CPE, Another major fin ding was that N-acetyl-D-glucosamine (GlcNAc) which does not inhibit a dhesion of amoeba to host cells is also an inhibitor of amoeba-induced CPE. The Acanthamoebae are thought to produce CPE by secreting cytoto xic proteinases. By zymography, one metalloproteinase and three serine proteinases were detected in the conditioned media obtained after inc ubating amoebae with the host cells. The addition of free alpha-Man an d GlcNAc to the co-culture media inhibited the secretion of the metall oproteinase and serine proteinases, respectively. In summary, we have shown that the lectin-mediated adhesion of the Acanthamoeba to host ce lls is a prerequisite for the amoeba-induced cytolysis of target cells and have implicated a contact-dependent metalloproteinase in the cyto pathogenic mechanisms of Acanthamoeba.