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

Entamoeba histolytica adheres via galactose-lectin (Gal-lectin) to hum an colonic mucins and intestinal epithelial cells as a prerequisite to amebic invasion. Native Gal-lectin is a protective antigen in the ger bil 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 macrop hages (BMM), Resistance to amebiasis requires an effective cell-mediat ed immune response against E. histolytica trophozoites mediated bg nit ric oxide (NO) released from activated macrophages. Herein, we determi ne whether the TNF-alpha-stimulating region or Gal-lectin can activate gamma interferon (IFN-gamma)-primed BMM for NO production and amebici dal activity. Native Gal-lectin (100 to 500 ng/ml) stimulated TNF-alph a and inducible nitric oxide synthase (iNOS) mRNA expression in IFN-ga mma-primed BMM as did lipopolysaccharide (100 ng/ml). Primed BMM produ ced TNF-alpha and NO in response to Gal-lectin in a dose-dependent man ner. Antilectin monoclonal antibody 1G7, which recognizes a domain (am ino acids 596 to 818) of the TNF-alpha mRNA-stimulating region of Gal- lectin, specifically inhibited TNF-alpha and iNOS mRNA induction and T NF-alpha and NO production by primed BMM in response to Gal-lectin (10 0 ng/ml). Simultaneous treatment of BMM with IFN-gamma and Gal-lectin (100 ng/ml) activated the cells to kill E. histolytica trophozoites, w hereas IFN-gamma treatment alone had no effect. In the presence of mon oclonal antibody 1G7 or aminoguanidine (an iNOS inhibitor), NO product ion and amebicidal activity were inhibited >80%. These results suggest that the TNF-alpha-stimulating region of native Gal-lectin is a poten t stimulus of IFN-gamma-primed BMM for NO production, which is essenti al for host defense against amebiasis.