A large white blood cell , derived from monocytes (a subclass of Mononuclear Leukocytes ). Properties include phagocytosis and antigen presentation to T-cells . Macrophages contain granules or packets of chemicals and enzymes (such as IL1 ) which serve the purpose of ingesting and destroying microbes, antigens and other foreign substances.

Macrophages are not found in the bloodstream but at locations where body organs interface with the environment or the bloodstream. For example, in the lungs, spleen , bone marrow and liver. Similar cells in the blood are the monocytes .