Macrophage bacteria video animation. A macrophage is specialised cell called a phagocyte which is responsible for detecting and distroying harmful bacteria and organisms. Macrophages are formed through the differentiation of monocytes (white blood cells). When tissue gets damaged or there is an infection, the monocytes leave the bloodstream and enter the affected tissue or organ and undergo a series of changes to become macrophages. Free medical stock videos from animation company Polymime.