![Ruptured infected macrophages (in green) and mycobacteria (in magenta) growing extracellularly](https://www2.mrc-lmb.cam.ac.uk/wordpress/wp-content/uploads/Ruptured-infected-macrophages-and-mycobacteria-150x150.jpg)
Macrophages are a critical part of our immune system. They patrol our tissues, and when they encounter debris or invaders such as bacteria and parasites, they engulf the particles and destroy them. But if, in the course of tuberculosis, these infected macrophages die through a process called necrosis, in which the cells burst open, then the engulfed bacteria are released back into the extracellular environment where they can grow unrestricted.