Macrophages are a type of white blood cell that play an integral part in the immune system with the role of phagocytosing foreign antigens, such as bacteria. They are formed in response to an infection or accumulating damaged or dead cells. Macrophages have pivotal functions in homeostasis and many physiological processes beyond innate immunity, including metabolic function, clearance of cellular debris, tissue repair, and remodeling. Some of the key functions of macrophages are:

• Phagocytosis: Macrophages ingest and degrade dead cells, debris, tumor cells, and foreign materials. They play a role in destroying infectious organisms that enter the body, clearing cellular debris, and wound healing.

• Immune response: Macrophages have a defensive function against pathogens such as microbes. They are able to present antigens to other immune cells, such as T-cells, for further destruction.

• Tissue homeostasis: Macrophages promote homeostasis by responding to internal and external changes within the body, not only as phagocytes, but also through trophic, regulatory, and repair functions. They also play an important role in forming granulomas, which are aggregations of macrophages that function in walling off an infection.

• Waste disposal: Macrophages play an important role in the disposal of internal waste materials. They clear out debris and dead cells.

• Tissue repair: Macrophages have a role in tissue repair and remodeling. They also mediate repair through an anti-inflammatory response.

Macrophages are found in almost all organs in the body, including the liver, brain, bones, and lungs, and they have specific functions in each organ.