In vivo programmed cell death of Entamoeba histolytica trophozoites in a hamster model of amoebic liver abscess

Abstract

Entamoebahistolyticatrophozoites can induce host cell apoptosis, which correlates with the virulence of the parasite. This phenomenon has been seen during the resolution of an inflammatory response and the survival of the parasites. Other studies have shown thatE. histolyticatrophozoites undergo programmed cell death (PCD)in vitro, but how this process occurs within the mammalian host cell remains unclear. Here, we studied the PCD ofE. histolyticatrophozoites as part of anin vivoevent related to the inflammatory reaction and the host–parasite interaction. Morphological study of amoebic liver abscesses showed only a fewE. histolyticatrophozoites with peroxidase-positive nuclei identified by terminal deoxynucleotidyltransferase enzyme-mediated dUTP nick end labelling (TUNEL). To better understand PCD following the interaction between amoebae and inflammatory cells, we designed a novelin vivomodel using a dialysis bag containingE. histolyticatrophozoites, which was surgically placed inside the peritoneal cavity of a hamster and left to interact with the host’s exudate components. Amoebae collected from bags were then examined by TUNEL assay, fluorescence-activated cell sorting (FACS) and transmission electron microscopy. Nuclear condensation and DNA fragmentation ofE. histolyticatrophozoites were observed after exposure to peritoneal exudates, which were mainly composed of neutrophils and macrophages. Our results suggest that production of nitric oxide by inflammatory cells could be involved in PCD of trophozoites. In this modifiedin vivosystem, PCD appears to play a prominent role in the host–parasite interaction and parasite cell death.