Microbes and microbial toxins: Paradigms for microbial-mucosal interactions - VI. Entamoeba histolytica: parasite-host interactions

The protozoan intestinal parasite Entamoeba histolytica remains a significa nt cause of morbidity and mortality worldwide. E. histolytica causes two ma jor clinical syndromes, amebic colitis and amebic liver abscess. Recent adv ances in the development of in vitro and in vivo models of disease, new gen etic approaches, the identification of key E. histolytica virulence factors , and the recognition of crucial elements of the host response to infection have led to significant insights into the pathogenesis of amebic infection . E. histolytica virulence factors include 1) a surface galactose binding l ectin that mediates E. histolytica binding to host cells and may contribute to amebic resistance to complement, 2) amebapores, small peptides capable of lysing cells, which may play a role in killing intestinal epithelial cel ls, hepatocytes, and host defense cells, and 3) a family of secreted cystei ne proteinases that play a key role in E. histolytica tissue invasion, evas ion of host defenses, and parasite induction of gut inflammation. Amebae ca n both lyse host cells and induce their suicide through programmed cell dea th. The host response is also an important factor in the outcome of infecti on, and neutrophils may play a key role in contributing to the tissue damag e seen in amebiasis and in controlling amebic infection.