Direct and High-Throughput Assays for Human Cell Killing through Trogocytosis by Entamoeba histolytica

Abstract

Entamoeba histolytica is a microbial eukaryote and causative agent of the diarrheal disease amoebiasis. Pathogenesis is associated with profound damage to human tissues, and treatment options are limited. We discovered that amoebae attack and kill human cells through a cell-nibbling process that we named trogocytosis (trogo-: nibble). Trogocytosis is likely to underlie tissue damage during infection and it represents a potential target for therapeutic intervention, although the mechanism is still unknown. Assays in current use to analyze trogocytosis by amoebae have not been amenable to studying different types of human cells, or to high-throughput analysis. Here, we developed two complementary assays to measure trogocytosis by quantifying human cell viability, both of which can be used for suspension and adherent cells. The first assay uses CellTiterGlo, a luminescent readout for cellular ATP levels, as a proxy for cell viability. We found that the CellTiterGlo signal is proportional to the quantity of viable cells, and can be used to detect death of human cells after co-incubation with amoebae. We established a second assay that is microscopy-based and uses two fluorescent stains to directly differentiate live and dead human cells. Both assays are simple and inexpensive, can be used with suspension and adherent human cell types, and are amenable to high-throughput approaches. These new assays are tools to improve understanding of amoebiasis pathogenesis.