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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 3632

Francine Marciano-Cabral, Kathy L. Zoghby, and S. Gaylen Bradley; Cytopathic Action of Naegleria fowleri Amoebae on Rat Neuroblastoma Target Cells. J.Protozool. 37(2):138-144, 1990

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The axenically cultured, weakly pathogenic Naegleria fowleri LEE and the highly pathogenic, mouse passaged N. fowleri LEEmp are cytopathic for B103 rat nerve cells in culture. Cytopathogenicity was measured by release of radiolabeled rubidium or radiolabeled chromium from B103 target cells. Cytopathogenicity was time-dependent for up to 18 hr and dependent upon amoebae effector to nerve cell target ratios of less than 1:1. Release of [51Cr] from B103 cells by either LEE or LEEmp amoebae was enhanced by addition of calcium or magnesium to medium free of these divalent cations by the ion-channel inhibitor, verapamil, or the ionophore A23187 and phorbol myristate acetate did not alter release of [51Cr] from B103 cells cocultured with the amoebae. Cycloheximide or actinomycin D impaired release of [51Cr] from B103 target cells injured by either LEE or LEEmp amoebae. Both strains of amoebae were fractionated by glass bead disruption and high speed centrifugation into membrane and soluble fractions. Each fraction was incubated with either [86Rb] or [51Cr] labeled nerve cells. The membrane fraction from LEEmp was more active than the soluble fraction in facilitating rubidium and chromium release. In contrast, the soluble fraction from LEE was more active than the membrane fraction in facilitating rubidium release from radiolabeled target cells. The sequential release of [86Rb] and [51Cr] from target cells rather than the simultaneous release of the two isotopes indicates that target cell death is due to the release of ions followed later by the release of large macromolecules. The results indicate that N. fowleri amoebae injure nerve cells by two alternate mechanisms, trogocytosis or contact-dependent lysis.