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. 2022 Jan 19;27:100300. doi: 10.1016/j.jctube.2022.100300

Fig. 1.

Fig. 1

Seven Steps in the Pathophysiology of Active Tuberculosis. This figure demonstrates the pathophysiology of active tuberculosis. These steps are aerosolization, macrophage phagocytosis, phagolysosome blockage and replication, TH1 response, granuloma formation, clinical manifestations, and transmission. A) Aerosolization is the beginning and the end of the cycle of tuberculosis pathophysiology. Aerosolization occurs when a person with active tuberculosis forcefully expires through actions such as coughing. B) A susceptible person who breathes in the aerosolized Mycobacterium tuberculosis and droplets small enough to reach the alveolar sacs (shown in the first magnification) will encounter macrophages, dendritic cells, and monocytes. The macrophages will phagocytose the bacteria (shown in the second magnification) and attempt to destroy the invader. Dendritic cells will migrate to lymph nodes to activate T-helper cells. C) M. tuberculosis prevents the phagolysosome fusion, avoids destruction, begins replicating, and releases DNA, RNA, proteases, and lipids. Additionally, the macrophages will release cytokines and vascular endothelial growth factor (VEGF). The VEGF will trigger angiogenesis and increase vascularization to the lesion. The cytokines will initiate the innate response and recruit natural killer (NK) cells, dendritic cells (DC), neutrophils, and macrophages in different forms. D) The T-helper cell response will involve the migration of TH1, Tregs, and B cells primed in the germinal center. These cells will combine to form the granuloma (E). The granuloma is a prison to wall off the bacteria from spreading systemically. F) Later, or present, immunocompromisation prevents the granuloma from containing the bacteria. The bacteria will spread and multiply in multiple clinical manifestations. G) During this phase, the bacteria can be aerosolized by the original susceptible, now infected, host, and begin the cycle anew. Adapted from “Granuloma”, by BioRender.com (2021). Retrieved from https://app.biorender.com/biorender-templates.