Cigarette Smoke Increases Susceptibility to Tuberculosis—Evidence From In Vivo and In Vitro Models

Background. Cigarette smoke (CS) exposure is an epidemiological risk factor for tuberculosis, although the biological basis has not been elucidated. Methods. We exposed C57BL/6 mice to CS for 14 weeks and examined their ability to control an aerosol infection of Mycobacterium tuberculosis Erdman. Results. CS-exposed mice had more M. tuberculosis isolated from the lungs and spleens after 14 and 30 d, compared with control mice. The CS-exposed mice had worse lung lesions and less lung and splenic macrophages and dendritic cells (DCs) producing interleukin12 and tumor necrosis factor α (TNF-α). There were significantly more interleukin 10–producing macrophages and DCs in the spleens of infected CS-exposed mice than in non-CS-exposed controls. CS-exposed mice also showed a diminished influx of interferon γ–producing and TNF-α-producing CD4+ and CD8+ effector and memory T cells into the lungs and spleens. There was a trend toward an increased number of viable intracellular M. tuberculosis in macrophages isolated from humans who smoke compared with nonsmokers. THP-1 human macrophages and primary human alveolar macrophages exposed to CS extract, nicotine, or acrolein showed an increased burden of intracellular M. tuberculosis. Conclusion. CS suppresses the protective immune response to M. tuberculosis in mice, human THP-1 cells, and primary human alveolar macrophages.