What is the pathogenesis of tuberculosis?
Pathogenesis of Tuberculosis (TB) Tuberculosis is caused by the bacterium Mycobacterium tuberculosis . Its pathogenesis is primarily based on the host immune response to the infection, which leads to the formation of granulomas — a hallmark of TB. The bacteria can persist in a latent state or cause active disease, depending on the host’s immunity. Step-by-Step Pathogenesis 1. Inhalation of Bacilli Infection begins when M. tuberculosis is inhaled in airborne droplets. The bacilli reach the alveoli of the lungs. 2. Phagocytosis by Alveolar Macrophages Alveolar macrophages engulf the bacilli. M. tuberculosis inhibits phagosome-lysosome fusion , allowing it to survive and replicate inside the macrophage. 3. Immune Activation (within 2–3 weeks) Infected macrophages release cytokines (e.g., IL-12) and present TB antigens to CD4+ T-helper cells (Th1) . Th1 cells release interferon-gamma (IFN-γ) , activating macrophages to kill ingested bacilli. 4. Granuloma F...