Entamoeba histolytica: mechanism of surface receptor capping

Binding of antibodies to the surface of the parasitic protozoan Entamoeba histolytica induces capping and release of antigen-antibody complexes, in a process that may be an effective means of evading the host immune response. To analyze the mechanism of capping in E. histolytica trophozoites, optimal conditions were determined for cap induction by sera from patients with amebic liver abscess, by polyclonal anti-amebic antibodies, and by concanavalin A. Cocapping of actin and myosin was documented by immunofluorescent staining of capped amebas using phalloidin, monoclonal anti-actin antibodies, and polyclonal anti-myosin antibodies. Immunoblots confirmed the presence of actin and myosin in isolated caps. These observations demonstrate that amebic cytoskeletal components participate in E. histolytica capping of surface receptors.