Roles for the galactose-/N-acetylgalactosamine-binding lectin of Entamoeba in parasite virulence and differentiation

Entamoeba histolytica, an intestinal protozoan parasite, is a major cause of morbidity and mortality in developing countries. The pathology of the disease is caused by the colonization of the large intestine by the amoebic trophozoites and the invasion of the intestinal epithelium. Some of the trophozoites will eventually differentiate into the infectious cyst form, allowing them to be transmitted out of the bowel and into water supplies to be passed from person to person. Both the virulence of the organism and the differentiation process relies on a galactose-/N-acetylgalactosamine (GalNAc)-binding lectin that is expressed on the surface of trophozoites. The functional activity of this lectin has been shown to be involved in host cell binding, cytotoxicity, complement resistance, induction of encystation, and generation of the cyst wall. The role of the lectin in both differentiation and virulence suggests that it may be a pivotal molecule that determines the severity of the infection from a commensal state resulting from increased encystation to an invasive state. The lectin-glycan interactions that initiate these diverse processes are discussed with emphasis on comparing the binding of host ligands and the interactions involved in encystation.