ENTAMOEBA-HISTOLYTICA MODULATES THE NITRIC-OXIDE SYNTHASE GENE AND NITRIC-OXIDE PRODUCTION BY MACROPHAGES FOR CYTOTOXICITY AGAINST AMEBAS AND TUMOR-CELLS

Nitric oxide (NO) is the major cytotoxic molecule produced by activate d macrophages for cytotoxicity against Entamoeba histolytica trophozoi tes. In the present study, we determined whether E. histolytica infect ion and soluble amoebic proteins affected macrophage cytotoxicity agai nst amoebae and tumour cells by modulating the inducible NO synthase g ene (iNOS) and NO (measured as nitrite, NO2-) and tumour necrosis fact or-alpha (TNF-alpha) production. Amoebic liver abscess-derived macroph ages [days 10, 20, 30 post-infection (p.i.)] stimulated with interfero n-gamma (IFN-gamma) and lipopolysaccharide (LPS) showed increased cyto toxicity against L929 cells (TNF-alpha-sensitive), but were refractory for killing amoebae and P815 cells (both NO-sensitive), concomitant w ith low NO2- production (< 4 mu M/10(6) cells). In contrast, peritonea l and spleen macrophages at 10 and 20 days p.i. activated with IFN-gam ma and LPS demonstrated increased killing of amoebae, and L929 and P81 5 cells concomitant with high NO2- production (> 12 mu M/10(6) cells). Pretreatment of mouse bone marrow-derived macrophages with amoebic pr oteins suppressed IFN-gamma and LPS-induced amoebicidal (33%) and tumo ricidal (44-49%) activities, with a corresponding decrease in TNF-alph a (56%) and NO (41%) production as well as TNF-alpha (41%) and iNOS (2 7%) mRNA by Northern blot analyses as compared to untreated activated controls. Inhibition of prostaglandin E(2) (PGE(2)) biosynthesis in ab scess and naive macrophages pretreated with amoebic proteins augmented IFN-gamma- and LPS-induced killing of L929 cells and TNF-alpha produc tion, but failed to increase killing of P815 cells and amoebae as well as iNOS mRNA levels or NO production. These results suggest that E. h istolytica selectively induces dysfunction of macrophage cytotoxicity by modulating iNOS mRNA expression and NO production independent from TNF-alpha and PGE(2) allowing the parasites to survive within the host by impairing host immune responses.