Role of cysteine proteinases of Entamoeba histolytica on the cytopathogenicity of axenic trophozoites on rat and hamster hepatocytes in vitro.

The role of amebic cysteine proteinase(s) on the in vitro cytotoxic and cytolytic effects of axenic trophozoites of a virulent strain (HM-1) of Entamoeba histolytica has been studied using freshly isolated rat and hamster hepatocytes as target cells. The cytotoxic effect was defined as cell killing without loss of cell structure and the cytolytic effect as cell disintegration. Incubation experiments of axenic trophozoites with rat or hamster liver cells in the presence and absence of bovine serum, of several proteinase inhibitors, and of galactose, galactosamine, and cysteine, at various ameba:liver cell ratios, different temperatures, and for several time periods, suggest that amebic cysteine proteinase is not involved in the cytotoxic effect but is essential for the cytolytic effect. This suggestion is supported by additional observations made with Transwell chambers, which effectively prevent contact between amebas and target cells, and by experiments with a fraction of an extract of lysed amebas that contained most of their cysteine proteinase activity.