35] Galactose-specific adhesion mechanisms of Entamoeba histolytica: Model for study of enteric pathogens

Abstract

This chapter discusses the evidence indicating that adhesion of Entamoeba histolytica is mediated by a galactose-inhibitable lectin and presents a method used to analyze the subunit structure of the adhesion protein. These investigations serve as a model to approach lectin–carbohydrate interactions of other pathogenic microorganisms. Adhesion to intestinal mucins, epithelium, and neutrophils is essential to the pathogenicity of E. histolytica. Initial efforts to characterize the nature of amebic adhesion focused on cell–cell interactions between amebic trophozoites and various target cells. The rosetting assay is described in the chapter in which Chinese hamster ovary (CHO) cells are bound by E. histolytica trophozoites and rosettes quantified in a hemacytometer chamber. Using the assay adhesion and contact-dependent cytolysis of CHO cells by trophozoites is shown to be completely blocked by millimolar concentrations of galactose and N-acetylgalactosamine (GalNAc), but not by other oligosaccharides, including N-acetylglucosamine, glucose, or mannose. In addition to adhesion, cell-contact dependent cytolysis has also been shown to be dependent on the galactose-inhibitable lectin using two different strategies. In the first, galactose or GalNAc is shown to inhibit amebic lysis of CHO cells completely. In the second approach, amebic binding and cytolysis of CHO cell glycosylation mutants are compared using cell-sorter methodology.