The life cycle of M. tuberculosis

The infection is initiated when Mtb bacilli, present in exhaled droplets or nuclei, are inhaled and phagocytosed by resident alveolar macrophages. The resulting proinflammatory response triggers the infected cells to invade the subtending epithelium. This response also leads to the recruitment of monocytes from the circulation, as well as extensive neovascularization of the infection site. The macrophages form the granulomas along with epithelioid cells, multinucleate giant cells, and foamy cells filled with lipid droplets, a fibrous cuff of extracellular matrix material may form. Progression toward disease is characterized by the loss of vascularization, increased necrosis, and the accumulation of caseum in the granuloma centre.