TB bacteria infecting macrophages. Coloured scanning electron micrograph (SEM) of Mycobacterium tuberculosis bacteria (pink) invading macrophage white blood cells (green). Macrophages are cells of the body’s immune system that phagocytose and destroy pathogens, dead cells and cellular debris. TB infection begins when the mycobacteria reach the pulmonary alveoli in the lungs, where they invade and replicate within the endosomes of alveolar macrophages.
Credit: SCIENCE PHOTO LIBRARY