Tuberculosis
Chronic granulomatous infection with Mycobacterium tuberculosis, contained by cell-mediated immunity into a latent state in most people, but able to reactivate into active, transmissible disease when that containment fails.
First principles
TB is a battle between a slow-growing organism and cell-mediated immunity
Mycobacterium tuberculosis is inhaled as droplet nuclei and reaches the alveoli, where its thick, waxy mycolic-acid cell wall resists killing by macrophages. Rather than being cleared, the organism survives inside macrophages, and the immune system's response is to wall it off in a granuloma (a structured collection of macrophages, epithelioid cells and lymphocytes) rather than eradicate it. This produces the central fact of TB biology: most infections become latent, not active, because containment, not clearance, is the usual outcome.
Educational content pending clinical review. Not medical advice.