ABSTRACT
PURPOSE: Toxoplasma gondii is an intracellular protozoan parasite and the most common cause of infectious uveitis. This study was conducted to evaluate the in vitro effect of tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma in rat retinal cells infected with T. gondii. METHODS: Rat retinal cells, retinal pigment epithelial (RPE) cells, and retinal Müller glial (RMG) cells were in vitro infected with T. gondii RH strain tachyzoites. Cultured cells were stimulated with various concentrations of TNF-alpha and IFN-gamma. The effect of TNF-alpha and IFN-gamma in T. gondii invasion and replication between retinal cells was determined through two different methods: measuring [(3)H]-uracil incorporation and counting infected cells by microscopic examination. RESULTS: Infection by T. gondii was lesser within RPE cells than within RMG cells. IFN-gamma significantly inhibits [(3)H]-uracil incorporation in RMG and RPE cells (respectively, 35%, 83%, and 87% inhibition at 0.1, 1, and 10 ng/mL for RMG cells and 0%, 30%, and 75% for RPE cells). TNF-alpha significantly inhibits [(3)H]-uracil incorporation in RPE cells (23% and 38% inhibition at 1 and 10 ng/mL), but not in RMG cells. These results were confirmed by confocal microscopic data. The percentage of infected cells decreased from 20% to 7% after IFN-gamma stimulation. CONCLUSIONS: Both cytokines IFN-gamma and TNF-alpha inhibited T. gondii replication in the RPE cells, whereas only IFN-gamma had an anti-Toxoplasma activity within the RMG cells. The differences in cytokine response may be the reason that RPE cells are less efficiently infected by T. gondii than are RMG cells.
Subject(s)
Connective Tissue Cells/parasitology , Interferon-gamma/pharmacology , Retina/cytology , Retinal Pigment Epithelium/parasitology , Toxoplasma/drug effects , Toxoplasma/physiology , Tumor Necrosis Factor-alpha/pharmacology , Animals , Cells, Cultured , Connective Tissue Cells/drug effects , Connective Tissue Cells/metabolism , Fluorescent Antibody Technique, Indirect , Microscopy, Confocal , Microscopy, Fluorescence , Nitric Oxide/metabolism , Rats , Rats, Inbred Lew , Recombinant Proteins , Retinal Pigment Epithelium/drug effects , Retinal Pigment Epithelium/metabolism , Uracil/metabolismABSTRACT
The proteasome, a large non-lysosomal multi-subunit protease complex, is ubiquitous in eukaryotic cells. In protozoan parasites, the proteasome is involved in cell differentiation and replication, and could therefore be a promising therapeutic target. This article reviews the present knowledge of proteasomes in protozoan parasites of medical importance such as Giardia, Entamoeba, Leishmania, Trypanosoma, Plasmodium and Toxoplasma spp.
Subject(s)
Cysteine Endopeptidases/physiology , Eukaryota/enzymology , Multienzyme Complexes/physiology , Protease Inhibitors/therapeutic use , Protozoan Infections/parasitology , Animals , Antiprotozoal Agents , Cysteine Endopeptidases/chemistry , Cysteine Endopeptidases/ultrastructure , Entamoeba/enzymology , Entamoeba/physiology , Eukaryota/physiology , Giardia/enzymology , Giardia/physiology , Leishmania/enzymology , Leishmania/physiology , Multienzyme Complexes/chemistry , Multienzyme Complexes/ultrastructure , Plasmodium/enzymology , Plasmodium/physiology , Proteasome Endopeptidase Complex , Toxoplasma/enzymology , Toxoplasma/physiology , Trypanosoma/enzymology , Trypanosoma/physiologyABSTRACT
We examined the in vitro effect of increasing gliotoxin concentrations on the infectivity of Toxoplasma gondii for NIH-3T3 murine fibroblasts and on Toxoplasma chymotrypsin-like activity, which is specific to the proteasome. Parasite penetration of host cells was not modified by a high gliotoxin concentration (1 microM), but replication was markedly decreased (approximately 50% inhibition by 0.5 microM gliotoxin). Gliotoxin reduced the chymotrypsin-like activity of the Toxoplasma proteasome, but five times less potently than in HeLa cells.
