A heat-labile material with cytotoxic and enterotoxic activities was isolated from axenically cultivated Entamoeba histolytica. The cytotoxin-enterotoxin was partially purified from the particulate-free supernatant of sonicated trophozoites by ammonium sulfate precipitation and gel filtration. Cytotoxic activity, assayed on monolayers of HeLa or BHK-21 cells, was restricted to proteins that eluted in the molecular weight range of 25,000--35,000 daltons. Cytotoxicity was demonstrated at protein concentrations as low as 2--4 microgram/ml, was heat-labile (75 C, 30 min), and was inhibited by specific immune IgG and by an undetermined factor in nonimmune serum. Enterotoxic activity of the partially purified toxin was demonstrated by induction of fluid secretion in ligated rabbit ileal loops. The cytotoxin-enterotoxin of E. histolytica may play an important role in the production of diarrhea and mucosal injury in amoebic colitis.

No abstract

Internalization of particulates and liquids (endocytosis) and the assymilation of ingested foodstuffs have been well documented for several free living amebae (Pelomyxa and Acanthamoeba). Less is known about these processes in the human parasitic ameba, Entamoeba histolytica.Axenically cultivated trophozoites of E. histolytica, strain HM-1:IMSS, were studied by transmission electron microscopy of thin sections and freeze-etch replicas prepared from cells incubated (5 min to 3 hr) with latex beads, erythrocytes or bacteria.Tubular channels formed by plasmalemma invagination appeared to be associated with pinocytosis (Fig. 1). These were similar to the pinocytotic channels described by Chapman-Andreson and Nilsson for Pelomyxa.