title: The interaction of human T-lymphocytes and Entamoeba histolytica: killing of virulent amoebae by lectin-dependent lymphocytes.
abstract: Clinical and experimental studies indicate that following invasive disease due to Entamoeba histolytica, development of human cell-mediated immune mechanisms may provide protective immunity. Activated, human monocyte-derived macrophages in vitro can kill virulent axaenic amoebic trophozoites. This study describes the interaction of lectin-stimulated T-lymphocytes and E. histolytica trophozoites (virulent strain HM1-IMSS). Amoebae progressively killed unstimulated nonimmune T-lymphocytes over 18 h incubation with no effect on amoebic viability. T-lymphocytes, stimulated with phytohaemagglutinin (PHA), were progressively cytotoxic for virulent HMI amoebae over 18 h incubation, but were also reduced in viability themselves. Lymphocyte cytotoxicity for amoebae was absent if PHA was removed before or added only during the assay. PHA-stimulated T-lymphocytes killed amoebae at cell ratios of lymphocytes to amoebae as low as 50:1 and cytotoxicity was antibody-independent. PHA-stimulated T-lymphocytes, depleted of T8-bearing cells by complement-mediated lysis, were unable to kill amoebae. Adherence of PHA-stimulated T-lymphocytes to amoebae was greater than with unstimulated T-lymphocytes. Inhibition of the amoebic adherence lectin with N-acetyl-D-galactosamine decreased lymphocyte-amoebic adherence and resulted in increased lymphocyte amoebicidal activity and lymphocyte survival. Suspension of amoebae with or without adherent PHA-stimulated T-lymphocytes in a 10% dextran solution indicated that cytotoxicity was contact dependent. In summary, PHA-stimulated T-lymphocytes of the T8-phenotype can kill virulent axaenic E. histolytica trophozoites through a contact-dependent, antibody-independent mechanism.
mesh_terms: D000818:Animals; D002448:Cell Adhesion / Q000187:drug effects; D002470:Cell Survival; D003165:Complement System Proteins / Q000276:immunology; D003602:Cytotoxicity, Immunologic; D003911:Dextrans / Q000494:pharmacology; D004748:Entamoeba histolytica / Q000276:immunology / Q000502:physiology*; D006801:Humans; D008213:Lymphocyte Activation / Q000187:drug effects; D010835:Phytohemagglutinins / Q000494:pharmacology*; D013602:T-Lymphocytes, Cytotoxic / Q000187:drug effects / Q000276:immunology*
chemical_list: D003911:Dextrans; D010835:Phytohemagglutinins; D003165:Complement System Proteins