Surface properties of Entamoeba: increased rates of human erythrocyte phagocytosis in pathogenic strains.

Abstract

Amebiasis is one of the most frequent protozoan infections of man, because an estimated 10% of the world population is affected (1). The disease is caused by Entamoeba histolytica, the only Entamoeba known to be pathogenic for humans. The motile form or trophozoite can live in the intestinal lumen as a harmless commensal, but occasionally, and for unknown reasons, it can invade the colonic mucosa giving rise to amebic dysentery and subsequently to liver abscesses (2). In addition to E. histolytica, nonpathogenic Entamoeba species like Entamoeba coli, and Entamoeba hartmanni may inhabit the human intestine. The reasons for the different behavior of pathogenic and nonpathogenic Entamoeba are not known.Basic structural or biochemical differences which could account for the erratic invasive behavior of Entamoeba have not been found (3, 4). However, pathogenic strains of E. histolytica differ from strains isolated from asymptomatic carriers and other nonpathogenic Entamoeba in certain surface properties, such as the susceptibility to agglutinate with the plant lectin concanavalin A, and the lack of surface charge (5, 6).Another surface property characteristic of Entamoeba is the ability to phagocytize a variety of particulate material including starch grains, bacteria, various protozoa, inert polyestyrene beads, and erythrocytes (7-16). More than 100 yr ago Lesh (LiSsch) (17) demonstrated that amebas in stool samples from human dysentery contained erythrocytes. Since then, it has been claimed repeatedly that invasive strains of E. histolytica are the only intestinal amebas of humans able to ingest erythrocytes. Erythrophagocytosis has been traditionally considered as one of the most important criteria in identifying pathogenic E. histolytica trophozoites, as a perusal of texts on human protozoology will reveal (1, 18-25) with few exceptions (2).In view of the importance given to the presence of ingested erythrocytes for the identification of invasive E. histolytica, the lack of systematic comparative studies is striking. On one hand, Entamoeba other than E. histolytica have occasionally been shown to engulf erythrocytes both in vivo and in vitro (16,26,27). On the other hand, studies on E. moshkovskii (the only free-living Entamoeba known) are contradictory, because it has been reported to be able (28) or unable (29) to phagocytize erythrocytes. Shaffer and Ansfield (30) studied the erythrophagocytosis in a number of E. histolytica strains without specifying their virulence.In continuation of our studies on the surface properties of Entamoebae (5, 6) we have

Laboratory Diagnostic Techniques for Entamoeba Species

“…The specificity of this finding was further reduced when it was demonstrated that in some patients E. dispar also contains RBCs (80). In vitro studies have also confirmed the ability of E. dispar to ingest RBCs (191). In one study, the specificity of E. histolytica/E.…”

VH3 Gene Usage in Neutralizing Human Antibodies Specific for theEntamoeba histolyticaGal/GalNAc Lectin Heavy Subunit

“…Erythrophagocytosis of E. histolytica was assayed as previously described (47). Briefly, trophozoites (10 4 cells) of HM-1:IMSS were exposed to 100 g of each Fab at 37°C for 30 min and then washed with ice-cold PBS.…”

Apoptotic Killing and Phagocytosis of Host Cells by the ParasiteEntamoeba histolytica

“…Amebic cytotoxicity and phagocytic ability both correlate with parasite virulence (21,23,24,26,31,35). Indeed, the observation of ingested host cells is the only characteristic on light microscopy that distinguishes E. histolytica from the nonpathogenic intestinal commensal organism Entamoeba dispar (16).…”