We examined the effect of bafilomycin A1 (BAF), an inhibitor of vacuolar-type H(+)-ATPases, on macrophages activation (measured as increased nitrite production and leishmanicidal activity) induced by interferon gamma alone or together with lipopolysaccharide or tumour necrosis factor alpha. BAF increased intravesicular pH and enhanced nitrite release by activated macrophages; however, the NO concentration necessary to kill parasites was higher in BAF-exposed than control macrophages, suggesting that microbicidal nitrogen derivatives were less active at alkaline pH. Antibody to tumour necrosis factor alpha inhibited BAF-induced nitrite production in interferon-activated cultures. To determine if enhanced NO synthesis was related to vesicular alkalinization, macrophages were incubated with the lysosomotropic bases NH4Cl and methylamine. These agents also increased intravesicular pH and nitrite production. Nitrite production was correlated with enhanced NO synthase activity in cytosolic extracts of the activated cells.

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