ROLE OF REACTIVE NITROGEN AND OXYGEN INTERMEDIATES IN GAMMA-INTERFERON-STIMULATED MURINE MACROPHAGE BACTERICIDAL ACTIVITY AGAINST BURKHOLDERIA-PSEUDOMALLEI

We examined the contributions of reactive nitrogen and oxygen intermed iates (RNI and ROI, respectively) in macrophage bactericidal activity against Burkholderia pseudomallei, the causative agent of melioidosis, in order to understand host defense mechanisms against infection caus ed by this bacterium. The bacteria multiplied in unstimulated murine m acrophage cell line J774.1. However, a strong dose-dependent inhibitio n of intracellular bacterial growth was observed when gamma interferon (IFN-gamma)-activated macrophages were used. The induction of bacteri cidal activity correlated well with the production of nitric oxide (NO ) by IFN-gamma-activated macrophages and was markedly suppressed by N- G-monomethyl L-arginine (L-NMMA), a competitive inhibitor of NO synthe sis. Superoxide dismutase (SOD) and catalase significantly inhibited m acrophage bactericidal activity, and the combined addition of L-NMMA, SOD, and catalase resulted in the complete inhibition of IFN-gamma-sti mulated activity. The bacteria were susceptible to the killing effects of chemically generated NO and superoxide anion in a macrophage-free system. Our results indicate that IFN-gamma-induced macrophage bacteri cidal activity against B. pseudomallei is mediated to a large extent b y RNI killing mechanisms and to a lesser extent by ROI-dependent mecha nisms.