The disease most commonly thought of as tuberculosis is a secondary disease caused by reactivation of organisms that were not eliminated and remained latent after the primary infection.
Primary infections are generally asymptomatic.
In the primary infection, inhaled organisms in the lower lobes are ingested by pulmonary macrophages. The organisms multiply intracellularly, both in the pulmonary macrophages and in the non-resident macrophages that collect in the area. The infected cells migrate through the lymphatics to the hilar lymph nodes and then seed areas of high oxygen tension, e.g., upper lobes of the lungs, base of the brain, and epiphyses of the long bones. Inflammation will be present at the primary site of infection and in the hilar lymph nodes. These are healed lesions that occur when immunocompetant lymphocytes encounter M. tuberculosis-containing macrophages.