https://www.sciencedaily.com/releases/2020/11/201124122925.htm > TB is a disease caused by the bacterium Mycobacterium tuberculosis (M. tuberculosis) and most often affects the lungs. The model reveals that respiratory system cells, called alveolar epithelial cells, play an essential role in controlling early TB infection. They do this by producing a substance called surfactant -- a mixture of molecules (lipids and proteins) that reduce the surface tension where air and liquid meet in the lung. > These findings add to our understanding of what happens during early TB infection, and may explain in part why those who smoke or have compromised surfactant functionality have a higher risk of contracting primary or recurrent infection.