Role of Adherence in Cytopathogenic Mechanisms of Entamoeba Histolytica

Abstract

The enteric pathogen, Entamoeba his-tolytica, appears to cause disease by adhering to and then destroying mucosal barriers. Using an in vitro method of studying the interaction of E. histolytica with target cells (Chinese hamster ovary [CHO] and human erythrocytes [RBC]), we examined the mechanism of amebic adherence and its role in lysis of target cells. Killing and phagocytosis of target cells by amebas ceases at 40C, allowing observation of adherence. Amebas adhere to CHO cells at 40C, 78.9% formed rosettes (amebas with .3 adherent CHO cells each) at 2 h. At 37°C, cytochalasins B and D inhibit adherence of amebas to CHO cells (P < 0.0005). Amebas adhere to and kill CHO cells in media with <0.1 ,uM calcium and magnesium plus 10 mM EDTA, indicating that divalent cations are not required in the medium. Adherence of amebas to human RBC was not ABO blood group specific and showed greater adherence to human than bovine or sheep RBC (P < 0.005). Neither Fc nor complement receptors were found on amebas by standard rosette studies. The amebic adherence receptor is not trypsin (0.125%) sensitive nor inhibited by trypan blue (1 mM). N-acetyl-D-galactosamine (GALNAc) inhibited the adherence of amebas to CHO cells and human RBC (0.1 g/100 ml or 4.5 mM GALNAc, P < 0.005) by binding to a receptor on the amebic surface. GALNAc abolishes amebic cytolysis of target CHO cells (determined by "lIndium oxine release from CHO cells, P < 0.001) but not amebic phagocytosis of CHO cells. By suspend