Animation showing the response of a macrophage (purple) to invading foreign particles (brown) which have entered the body through a skin wound. Macrophages are part of the body's innate immune defence, they are large cells of irregular shape which phagocytose (ingest) bacteria, debris or other foreign materials. Initially the macrophage adheres to the particle before forming pseudopods which engulf it. The engulfed particle is then broken down and destroyed.