Fig. 4.

Schematic representation of different outcomes and states after MTB infection of the host. The first outcome is active tuberculosis (ATB), where granulomas rupture allowing MTB to multiply in large numbers and enter the alveoli and surrounding tissues, causing the development of ATB. This condition commonly occurs in individuals with a weakened immune system, such as those with HIV infection or receiving immunosuppressive therapy, or in people with impaired immune function due to other reasons. The second outcome is TB elimination, which occurs when the immune response is sufficient to clear the MTB infection. The third outcome is an intermediate state, where MTB becomes dormant and stops replicating when the host can restrain its virulence or when MTB loads are low, leading to an LTBI, incipient TB, or subclinical TB, that may reactivate when the immune system becomes impaired. The upper part of this figure is a modification of Fig. 1 by Drain et al. [128], 2018. MTB Mycobacterium tuberculosis, TB tuberculosis, LTBI latent tuberculosis infection, ALF airway lining fluid