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Cytopathogenicity of Entamoeba histolytica
Abstract:
The lesions induced in man by Entamoeba histolytica are characterized by massive tissue injury in the absence of major local signs of a host immune response. The amoeba damages surrounding cells preferentially by contact-mediated cytolysis. Recently, a presumptive aetiological factor underlying this process has been identified. It is a protein, amoebapore, capable of spontaneous incorporation into host cell membranes. Therein it induces high conductance ion-channels which rapidly collapse the cellular transmembrane potential and lead to a prelytic state. Amoebapore is present within the amoeba in a highly aggregated state in a small, dense particle. It is shed into the medium in a particulate form by a stimulus-mediated process. Release is enhanced by addition of concanavalin A, lipopolysaccharide or the calcium ionophore A23187. Surface-labelling of intact amoeba, followed by fractionation of the homogenate in self-generating Percoll gradients, identified two labelled fractions, the plasma membrane and a particulate fraction sedimenting in the region of intracellular particulate amoebapore. This latter fraction appears to be material in the process of exocytosis. A highly immunogenic surface lipid has been identified and shown to be involved in the rapid surface redistribution of immune complexes, their shedding and endocytosis. The relevance of these findings to the immunoprophylaxis of amoebiasis is discussed.
Insights
Entamoeba histolytica causes tissue damage via amoebapore protein, which forms ion channels in host cells. This protein is released in particles, potentially aiding in immunoprophylaxis strategies for amoebiasis.
Area of Science:
- Cell biology
- Immunology
- Parasitology
Background:
- Entamoeba histolytica induces significant tissue injury with minimal host immune response.
- Cell damage is primarily mediated by contact-dependent cytolysis.
- A protein, amoebapore, has been identified as a key factor in this cytolysis.
Purpose of the Study:
- To investigate the mechanism of cell damage by Entamoeba histolytica.
- To characterize the role and release of amoebapore.
- To explore the involvement of surface lipids in immune complex dynamics.
Main Methods:
- Studied amoebapore's ability to form ion channels in cell membranes.
- Investigated stimulus-mediated release of amoebapore in particulate form.
- Utilized surface labeling and Percoll gradient fractionation to identify cellular fractions involved in amoebapore release.
- Identified and analyzed a surface lipid's role in immune complex behavior.
Main Results:
- Amoebapore spontaneously incorporates into host cell membranes, forming ion channels that disrupt transmembrane potential.
- Amoebapore is stored in aggregated particles and released via exocytosis, enhanced by specific stimuli (concanavalin A, LPS, A23187).
- A highly immunogenic surface lipid facilitates immune complex redistribution, shedding, and endocytosis.
Conclusions:
- Amoebapore is a critical virulence factor responsible for Entamoeba histolytica-induced cytolysis.
- Understanding amoebapore release mechanisms and surface lipid interactions is crucial for developing immunoprophylaxis against amoebiasis.