title: The tumor necrosis factor alpha-stimulating region of galactose-inhibitable lectin of Entamoeba histolytica activates gamma interferon-primed macrophages for amebicidal activity mediated by nitric oxide.
abstract: Entamoeba histolytica adheres via galactose-lectin (Gal-lectin) to human colonic mucins and intestinal epithelial cells as a prerequisite to amebic invasion. Native Gal-lectin is a protective antigen in the gerbil model of amebiasis. Amino acids 596 to 1082 of Gal-lectin mediate E. histolytica adherence to target cells and stimulate tumor necrosis factor alpha (TNF-alpha) production by naive murine bone marrow macrophages (BMM). Resistance to amebiasis requires an effective cell-mediated immune response against E. histolytica trophozoites mediated by nitric oxide (NO) released from activated macrophages. Herein, we determine whether the TNF-alpha-stimulating region of Gal-lectin can activate gamma interferon (IFN-gamma)-primed BMM for NO production and amebicidal activity. Native Gal-lectin (100 to 500 ng/ml) stimulated TNF-alpha and inducible nitric oxide synthase (iNOS) mRNA expression in IFN-gamma-primed BMM as did lipopolysaccharide (100 ng/ml). Primed BMM produced TNF-alpha and NO in response to Gal-lectin in a dose-dependent manner. Antilectin monoclonal antibody IG7, which recognizes a domain (amino acids 596 to 818) of the TNF-alpha mRNA-stimulating region of Gal-lectin, specifically inhibited TNF-alpha and iNOS mRNA induction and TNF-alpha and NO production by primed BMM in response to Gal-lectin (100 ng/ml). Simultaneous treatment of BMM with IFN-gamma and Gal-lectin (100 ng/ml) activated the cells to kill E. histolytica trophozoites, whereas IFN-gamma treatment alone had no effect. In the presence of monoclonal antibody 1G7 or aminoguanidine (an iNOS inhibitor), NO production and amebicidal activity were inhibited >80%. These results suggest that the TNF-alpha-stimulating region of native Gal-lectin is a potent stimulus of IFN-gamma-primed BMM for NO production, which is essential for host defense against amebiasis.
authors.affiliation: Institute of Parasitology of McGill University, Macdonald Campus, Quebec, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Séguin
authors.forename: B J
authors.initials: BJ
authors.lastname: Mann
authors.forename: K
authors.initials: K
authors.lastname: Keller
authors.forename: K
authors.initials: K
authors.lastname: Chadee
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D001853:Bone Marrow / Q000276:immunology*; D004748:Entamoeba histolytica / Q000276:immunology*; D004749:Entamoebiasis / Q000276:immunology; D005260:Female; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000494:pharmacology*; D037102:Lectins / Q000494:pharmacology*; D008264:Macrophages / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009569:Nitric Oxide / Q000096:biosynthesis / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D015800:Protozoan Proteins / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D000911:Antibodies, Monoclonal; D037102:Lectins; D015800:Protozoan Proteins; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; C078014:N-acetylgalactosamine inhibitable lectin 35-kDa subunit, Entamoeba histolytica; D009569:Nitric Oxide; D007371:Interferon-gamma; D019001:Nitric Oxide Synthase