Macrophages are needed in the progression of tuberculosis into lung cancer.

Although the association of tuberculosis (TB) and the development of lung carcinoma (LC) has been acknowledged, the underlying mechanism remains not clarified. Since sustained and repeated local inflammation and tissue remodeling have been suggested to be responsible for the high incidence of developing CL from TB, we hypothesize that macrophages may play a critical role in the process. To prove it, we induced TB in mice by injection of virulent Mycobacterium tuberculosis (MTB). Then the mice were allotted into two groups. One group received weekly tail vein injection of 20 μg saporin-conjugated antibody against the pan-macrophage surface marker CD11b to eliminate macrophages, while the other group received injection of control IgG in the same frequency. Six months later, the development of LC was determined by histology. We found that the occurrence of LC in TB mice that received macrophage depletion was significantly lower than those in control TB mice without macrophage intervention. These data suggest that macrophages may promote the progression of TB into LC.