Figure 5.

Nicotine induces T regulatory cells (Tregs) to produce transforming growth factor (TGF)-β, and nicotine-exposed Tregs impair macrophage activity against MTB infection. (A) Tregs isolated from FoxP3-EGFP reporter mice were incubated in medium alone or medium containing 0.1 and 1 μg/ml nicotine for 6 and 24 hours, and TGF-β levels measured in the supernatant. *P < 0.05, **P < 0.01, ***P < 0.001 compared with respective controls. (B) BMM from FoxP3-EGFP mice were cultured alone or cocultured with unexposed or nicotine-exposed Tregs at a ratio of 100 BMM:1 Tregs, and then infected with MTB. Intracellular MTB was quantified at 1 hour and 2 and 4 days after infection. (C) IL-10 concentration in the supernatant and (D) arginase activity—calculated from the urea assay—in whole-cell lysates were measured in the MTB-infected cell cultures. (E) Nitric oxide (NO₂⁻) concentration was measured in the supernatant of LPS + IFN-γ–stimulated BMM, MTB-infected BMM, MTB-infected BMM + unexposed Tregs, and MTB-infected BMM + nicotine-exposed Tregs. *P < 0.05, **P < 0.01 compared with BMM alone infected with MTB. Data shown are the mean (±SEM) of three independent experiments.