How does Mycobacterium tuberculosis affect the lungs?

Mycobacterium tuberculosis primarily affects the lungs by exploiting their oxygen-rich environment to thrive and persist within immune cells. When inhaled, the bacteria are trapped in lung tissue, triggering an immune response where phagocytic cells surround them to form hard, nodular tubercles.12

These tubercles consist of a central core of dead cells surrounded by immune cells and connective tissue. While the body often successfully sequesters the bacteria in a latent state, the infection can reactivate years later. During active pulmonary tuberculosis, the breakdown of these tubercles releases viable bacilli, leading to extensive tissue damage, cavity formation, and scarring.21

The resulting inflammation and granuloma formation—intended to contain the pathogen—can paradoxically cause significant harm to the lung's structure. As lesions erode nearby bronchi or blood vessels, patients may experience symptoms such as persistent cough, chest pain, and hemoptysis (coughing up blood). If left untreated, the progressive destruction of lung tissue reduces the capacity for gas exchange, ultimately leading to respiratory failure.32