السل

Tuberculosis is a chronic respiratory infection caused by Mycobacterium tuberculosis and spread through airborne droplet nuclei that carry the pathogen.

In the lungs, alveolar macrophages engulf the bacteria but can not destroy them.

The infected macrophages cross the alveolar epithelium, carrying the bacteria to the lung tissue.

As the bacteria multiply inside the macrophages, some of the macrophages die, releasing the bacteria into the lung tissue.

This causes an inflammatory response, drawing immune cells to the infection site.

Over time, these immune cells surround the infected area, creating a tight cluster called a granuloma that walls off the bacteria to contain the infection.

Inside the granuloma, most bacteria remain dormant. As a result, the host enters a clinically asymptomatic, noninfectious latent state.

If immunity is weakened by factors such as malnutrition or aging, these granulomas can break down and release the bacteria.

The bacteria then rapidly multiply in the lung tissue, causing inflammation and active symptomatic tuberculosis.