REACTIVE NITROGEN INTERMEDIATES IMPLICATED IN THE INHIBITION OF ENCEPHALITOZOON-CUNICULI (PHYLUM MICROSPORA) REPLICATION IN MURINE PERITONEAL-MACROPHAGES

Encephalitozoon cuniculi (phylum microspora) is a protozoan parasite t hat can replicate within parasitophorous vacuoles in macrophages. Thio glycollate-elicited BALB/c peritoneal macrophages treated with murine recombinant interferon-gamma (rIFN-gamma; 100 u/ml) in combination wit h lipopolysaccharide (LPS; 10 ng/ml) for 24 h killed E. cuniculi as de termined by significant reductions in the number of parasites and perc ent of infected macrophages 48 h later compared with cultures treated with medium only. Treatment of the elicited macrophages with murine rI FN-gamma (10 u/ml or 100 u/ml) only, resulted in microbistatic activit y. Significantly higher levels of nitrite (NO2) were detected in super natants from macrophage cultures treated with rIFN-gamma (10 u/ml or 1 00 u/ml) which induced microbistatic macrophage activity as well as fr om macrophage cultures treated with LPS + rIFN- when compared with lev els of nitrite detected in supernatants of infected ariginine analogue , N-3 monomethyl-L-arginine (NMMA) at concentrations of 50, 100 or 250 uM significantly inhibited nitrite synthesis and prevented microspori dia killing. Addition of exogenous L-arginine at concentrations of 5 m m or 10 mm reversed the NMMA-induced inhibition of parasite killing. T hese results indicate that reactive nitrogen intermediates contribute to the killing of E. cuniculi by LPS + rIFN-gamma-activated murine per itoneal macrophages in vitro.