FIGURE 3.

Pathophysiology of pulmonary TB. Upon entering the respiratory tract and lungs of the host, Mtb incites an innate immune response and is engulfed by pivotal immune cells such as macrophages and dendritic cells. Subsequently, Mtb replicates within these cells as more immune cells are recruited to the site of infection. Whilst it is possible for the host to completely eliminate Mtb at this stage, the formation of solid granulomas is often prompted. These granulomas are composed of foam cells derived from macrophages, as well as a multitude of necrotic immune cells, culminating in caseous granulomas that eventually rupture and release bacteria, giving way to the subsequent development of active TB. Ultimately, these Mtb bacteria are released as infectious aerosol droplets, reinstating a new cycle of infection. The elements in the figure were drawn using BioRender online tool (https://biorender.com).