FIG. 1.

Ability of catalase C-10 to inhibit antimycobacterial effects of IFN-γ- and LPS-activated J774.16 macrophages is associated with suppression of RNI production. Catalase C-10 (2,600 U/ml) was added to macrophage cultures 4 h prior to infection with M. tuberculosis Erdman. Macrophages (1.5 × 10⁵ cells per well in 96-well tissue culture plates) were primed with IFN-γ (250 U/ml) for 12 to 16 h. Supernatants were then removed and replaced with culture medium containing LPS (1 μg/ml) and M. tuberculosis Erdman (multiplicity of infection of 5 to 10:1) with or without catalase. Cultures were pulsed with [5,6-³H]uracil (specific activity, 34 Ci/mmol; New England Nuclear) at 24 h postinfection. After 16 to 24 h, cells and supernatants were assayed for [³H]uracil incorporation and NO₂⁻ content, respectively. Uninfected macrophages incorporated 1,500 to 4,000 cpm of [³H]uracil. Incorporation of label by nonactivated infected macrophages was in the range of 8,000 to 10,000 cpm. Nucleic acid synthesis by mycobacteria was measured as [³H]uracil incorporation by cultures with organisms minus that by control cultures (dcpm). The inhibitory effect of activated macrophages on mycobacteria was measured as percent suppression of [³H]uracil incorporation and expressed as follows: 100 × [1 − (dcpm for stimulated macrophages/dcpm for unstimulated macrophages)]. Data shown represent those of two independent experiments. SOD, superoxide dismutase. Error bars indicate standard errors. Asterisks indicate a P value of <0.05 (one-way analysis of variance; controls were samples without addition of scavenger).