Low susceptibility of trophozoites of virulent Entamoeba histolytica to cellular and antibody-dependent cellular cytotoxicity by guinea-pig effector cells.

Cytotoxic potentialities of lymphocytes and macrophages were determined against trophozoites of virulent and avirulent sublines of Entamoeba histolytica in vitro. Guinea-pigs were immunized with antigens of both sublines to obtain stimulated effector cells and antiamoebic antibodies. Trophozoites of an avirulent/attenuated subline of E. histolytica (NIH200) were significantly more susceptible to killing by lymphocytes and macrophages through cellular and antibody-dependent cellular cytotoxic mechanisms. The resistance of virulent trophozoites to killing was attributed to their higher phagocytic ability and virulence characteristics. Electron microscopic studies of the interactions showed that contact between the effector cells and the trophozoites was essential for the cytolytic event which resulted in disintegration of the trophozoites. Antigens of trophozoites of the virulence subline of E. histolytica (NIH200 V) were effective in inducing cytotoxicity against both virulent and avirulent trophozoites: however, the reverse was not true.