The role of Entamoeba histolytica trogocytosis (trogo-: nibble) in the pathogenesis of amoebiasis

About This Grant

Abstract Entamoeba histolytica is a pathogenic amoeba and the causative agent of amoebiasis in humans. Despite its impact on human health, E. histolytica is dramatically understudied. Currently, the only active NIH R01 on E. histolytica is in our laboratory, and it ends in May, 2025. The species name (histo-: tissue; lytic-: dissolving) derives from the capacity to destroy host tissues. E. histolytica trophozoites (“amoebae”) invade the large intestine, causing ulceration and can enter the bloodstream. Although it is rare, amoebae that have entered the bloodstream can disseminate to other tissues (e.g., the liver, lungs, or brain), causing fatal abscesses. Little is known of the mechanisms that allow E. histolytica to evade immune detection and to disseminate upon entering the bloodstream. Amoebae possess cell-killing activity that is likely to drive tissue damage. The accepted model was that amoebae kill human cells by secreting pore-forming amoebapore A. However, there is no evidence that amoebapore A or any other amoebic proteins are trafficked to human cells. We established a new paradigm in which amoebae kill by biting off human cell fragments, termed trogocytosis (trogo-: nibble) (Ralston, et al., Nature, 2014). We subsequently found that amoebae display human cell membrane proteins after performing trogocytosis and become protected from lysis by human complement (Miller, et al., mBio 2019). Here we propose to disentangle the cell killing models and further define this novel strategy for complement evasion via trogocytosis. We will apply imaging flow cytometry, host and amoeba mutants, and a variety of host cell types to dissect the contribution of trogocytosis to immune avoidance in vitro, and we will use the mouse model of amoebiasis to extend these findings to pathogenesis in vivo. Beyond E. histolytica, trogocytosis is a burgeoning theme that has far-reaching applications to eukaryotic biology. Several microbial eukaryotes use trogocytosis to kill other cells. In multicellular eukaryotes, trogocytosis is used for cell-killing, cell-cell communication and cell-cell remodeling, with roles in the immune system, central nervous system, and during development. Therefore, an improved understanding of trogocytosis will apply both directly to the pathogenesis of amoebiasis and broadly to eukaryotic trogocytosis in general. This work is innovative and high-impact as it will dramatically transform understanding of pathogenesis. We will define a novel strategy for immune evasion, reconcile new and old models for cell killing, and explore what makes E. histolytica virulent. Moreover, these studies apply to other infections, and to trogocytosis in general.