EFFECT OF INCREASING INTRAVESICULAR PH ON NITRITE PRODUCTION AND LEISHMANICIDAL ACTIVITY OF ACTIVATED MACROPHAGES

We examined the effect of bafilomycin A(1) (BAF), an inhibitor of vacu olar-type H+-ATPases, on macrophage activation (measured as increased nitrite production and leishmanicidal activity) induced by interferon gamma alone or together with lipopolysaccharide or tumour necrosis fac tor alpha. BAF increased intravesicular pH and enhanced nitrite releas e by activated macrophages; however, the NO concentration necessary to kill parasites was higher in BAF-exposed than control macrophages, su ggesting that microbicidal nitrogen derivatives were less active at al kaline pH. Antibody to tumour necrosis factor alpha inhibited BAF-indu ced nitrite production in interferon-activated cultures. To determine if enhanced NO synthesis was related to vesicular alkalinization, macr ophages were incubated with the lysosomotropic bases NH4Cl and methyla mine. These agents also increased intravesicular pH and nitrite produc tion. Nitrite production was correlated with enhanced NO synthase acti vity in cytosolic extracts of the activated cells.