title: Entamoeba histolytica: mechanism of decrease of virulence of axenic cultures maintained for prolonged periods.
abstract: Intraportal injection of non-virulent E. histolytica (derived from prolonged axenic culture of virulent E. histolytica) strain HM1-IMSS in normal hamsters results in no liver lesions and disappearance of the parasites 48-72 h after injection. Viability of non-virulent E. histolytica after 2 h of in vitro incubation in either fresh or decomplemented hamster serum is the same as control virulent E. histolytica (50-90%). In hamsters made leukopenic, or both leukopenic+hypocomplementemic, or hypocomplementemic+sephadex microspheres (to produce focal liver ischemia) intraportally injected non-virulent E. histolytica cause no lesions and disappear after 24 h. In addition, neither hypocomplementemia nor immunosuppression with cyclosporin A prolonged the survival of non-virulent E. histolytica. Methyl prednisolone treatment of hamsters resulted in survival of large numbers of non-virulent E. histolytica in the liver, with little inflammation and minimal tissue damage, for up to 7 days. Inflammatory cells (macrophages) would appear to be chiefly responsible for elimination of non-virulent E. histolytica. Parallel experiments with E. dispar suggest a different mechanism for its non-pathogenicity.
authors.affiliation: Department of Experimental Medicine, National Autonomous University of México Medical School, Mexico. olivosa@yahoo.com
authors.forename: Alfonso
authors.initials: A
authors.lastname: Olivos
authors.forename: Espiridión
authors.initials: E
authors.lastname: Ramos
authors.forename: Mario
authors.initials: M
authors.lastname: Nequiz
authors.forename: Carlos
authors.initials: C
authors.lastname: Barba
authors.forename: Eusebio
authors.initials: E
authors.lastname: Tello
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Castañón
authors.forename: Augusto
authors.initials: A
authors.lastname: González
authors.forename: Rubén D
authors.initials: RD
authors.lastname: Martínez
authors.forename: Irmgard
authors.initials: I
authors.lastname: Montfort
authors.forename: Ruy
authors.initials: R
authors.lastname: Pérez-Tamayo
mesh_terms: D000818:Animals; D006224:Cricetinae; D016572:Cyclosporine / Q000276:immunology; D004748:Entamoeba histolytica / Q000472:pathogenicity*; D005938:Glucocorticoids / Q000494:pharmacology; D007165:Immunosuppression Therapy; D007166:Immunosuppressive Agents / Q000276:immunology; D007970:Leukopenia / Q000276:immunology / Q000469:parasitology; D008099:Liver / Q000469:parasitology / Q000473:pathology; D008101:Liver Abscess, Amebic / Q000276:immunology / Q000469:parasitology* / Q000473:pathology; D008297:Male; D008647:Mesocricetus; D008775:Methylprednisolone / Q000494:pharmacology; D014774:Virulence
chemical_list: D005938:Glucocorticoids; D007166:Immunosuppressive Agents; D016572:Cyclosporine; D008775:Methylprednisolone