Artwork of a macrophage blood cell phagocyting some green, rod-shaped bacteria. Macrophages derive from monocytes (white blood cells) and are long-lived potent phagocytic cells which are able to engulf and digest foreign material. They are present throughout the connective tissue and around the basement membrane of small blood vessels. They are also highly concentrated in the lungs and liver where they filter off foreign material. Once activated, macrophages are able to ingest the bacteria inside their main body where they are destroyed by small particles called lysosomes.