Serum-independent and serum-dependent cytoadherence in the interaction of Entamoebahistolytica with mammalian target cells

Abstract

Entamoeba histolytica kills target cells'only on direct contact, suggesting that trophozoite-mediated cytolysis is initiated by the contact between trophozoites and target cells. We have shown that adherence between E. histolytica and target cells (polymorphonuclear granulocytes, erythrocytes, Chinese hamster ovary cells, human colon carcinoma cells) was inhibited by specific carbohydrates, and adherence between E. histolytica and polymorphonuclear granulocytes (PMN) was enhanced by preincubation of the trophozoites with serum. Inhibition of adherence clearly paralleled inhibition of cytolysis and phagocytosis of target cells. Cytolysis of PMN, however, was not increased by preincubation of the trophozoites with serum. These results suggest that the effector functions of trophozoites are only dependent on carbohydrate-specific adherence mechanisms mediated by the amoebic Gal/GalNAc-binding lectin. E. histolytica trophozoites themselves can be killed by PMN, depending on the virulence of the trophozoites. PMN could not kill E. histolytica trophozoites more effectively when the adherence was enhanced by preincubation of the trophozoites with serum or when adherence was only mediated by serumdependent mechanisms.