Fig. 1

Immunopathogenesis of tuberculosis. Infection occurs when Mtb enters the lung through the respiratory tract and then arrives in the alveolar space, where it faces macrophages residing in the alveolar space. Suppose this part of the immune system fails to kill Mtb. In that case, this bacteria attacks the interstitial tissue of the lung, which either infects the lung epithelial cells directly or is transmitted to the lung parenchymal tissue through the infected macrophages. Afterward, DCs or inflammatory monocytes lead to the transfer of Mtb to the lymph nodes of the lung for priming of T cells. The alliance of these events triggers the recruitment of immune cells, including B and T cells, to the lung parenchyma, resulting in granuloma formation. When the bacterial mass becomes too high, the granuloma can no longer control the infection, so the bacteria spread to other tissues, including the brain. At this stage, the bacteria can enter the bloodstream or re-enter the respiratory tract to be finally released. At this time, the infected host can transmit the infection to others, which is called active tuberculosis (Pai et al. 2016). Mtb: Mycobacterium tuberculosis; DCs: dendritic cells