Cysteine proteinase activity is required for survival of the parasite in experimental acute amoebic liver abscesses in hamsters

Abstract

Axenic trophozoites ofEntamoeba histolyticastrain HM1-IMSS grownin vitroin the presence of E-64, a potent irreversible inhibitor of cysteine proteinases, preserved their viability, their rate of replication, their resistance to complement, their haemolytic capacity and their ability to destroy target cells, despite complete inhibition of total cysteine proteinase activity. On the other hand, their erythrophagocytic capacity and their ability to decrease TER of MDCK cells was partially decreased. The same trophozoites injected into the portal vein of hamsters receiving a maintaining dose of E-64 failed to cause tissue damage and were rapidly eliminated. Our results suggest that amoebic cysteine proteinase activity is not required for amoebic functions inin vitroconditions, but that it becomes necessary for survival of trophozoites inin vivoconditions, whatever other role (if any) it may play in the parasite's virulence.