Macrophages in a mouse liver
Found in practically all tissues, macrophages (in blue) are the hungry cells of the immune system. They gobble up dying cells and harmful pathogens like bacteria to ensure tissues are happy and healthy. When a tissue is damaged, young macrophages are recruited by the bucket-load to the site of injury where they mature to speed up wound repair and eat trespassing bacteria. Some bacteria, like the one responsible for tuberculosis, can survive even after being eaten, eventually killing the macrophage and accelerating its spread within the tissue.
Image by Hendrik Herrmann.