Background:The aim of the present study was to determine if the inflammation and/or immunosuppression induced by Entamoeba histolytica may contribute to amebic invasion.Material/Methods: Dexamethasone was administered three days before and three days after inoculation of hamsters with E. histolytica. Seven days alter inoculation the animals were sacrificed and the sizes of their amebic liver abscesses were determined. The number of neutrophils, macrophages, T and B cells in the peritoneum as well as the production of nitric oxide and the susceptibility to Listeria monocytogenes infection was also determined.Results: Dexamethasone treatment significantly reduced the number of T lymphocytes in thymus and spleen. The number of neutrophils, macrophages and T lymphocytes in the peritoneal exudate was also reduced as well as the production of nitric oxide and the microbicidal activity against Listeria monocytogenes. However, in the animals treated with a high dose of dexamethasone the size of the liver abscesses was significantly smaller than in the untreated animals.Conclusions: The results suggest that macrophage and T cell-mediated immunity is not relevant as a protective mechanism because tissue invasion by E. histolytica was reduced in immunosuppresed animals. On the contrary, the inflammatory process may contribute to the invasion and liver damage.

Keywords: Entamoeba histolytica - immunology, Listeria monocytogenes - immunology, Liver Abscess, Amebic - immunology, Liver Abscess, Amebic - pathology, Liver Abscess, Amebic - prevention & control, B-Lymphocytes - immunology, Cricetinae, Dexamethasone - therapeutic use, Entamoeba histolytica - immunology, Immunosuppression, Immunosuppressive Agents - therapeutic use, Listeria monocytogenes - immunology, Liver Abscess, Amebic - prevention & control, Macrophages - immunology, Mesocricetus, Neutrophils - immunology, Nitric Oxide - metabolism, Peritoneum - pathology, Spleen - immunology, T-Lymphocytes - immunology, Thymus Gland - immunology