Macrophage

Article By:

Oakley, Oliver R. Department of Biological Sciences, Eastern Kentucky University, Richmond, Kentucky.

Last reviewed:August 2021

DOI:https://doi.org/10.1036/1097-8542.395760

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• Macrophages, published November 2015:Download PDF Get Adobe Acrobat Reader

Large phagocytic cells that detect, engulf, and destroy foreign particles, microbes, and other pathogens, as well as cellular debris. The immune system consists of many different types of cells, with each type having a unique function. In particular, macrophages (Fig. 1) are essential components of immune responses. Specifically, macrophages are scavengers; in fact, the term macrophage literally means “big eater,” which is an apt description of the action of a macrophage. Macrophages patrol the body's tissues, looking for foreign substances, cellular debris, and typically anything that is where it should not be. This includes pathogens, such as viruses, fungi, and bacteria. Macrophages are motile cells and are able to crawl along surfaces toward their target. Once foreign substances are detected by a macrophage, the substances are internalized by the macrophage through a process called phagocytosis and destroyed by complex enzymatic degradation. Moreover, macrophages are unique immune cells; they are the only cells of the immune system that are not found in the bloodstream. Instead, an inactive precursor cell, called a monocyte, circulates in the bloodstream and responds to chemical signals while flowing through tissues. In tissues that are experiencing a threat, such as a bacterial infection, the monocyte exits the bloodstream and enters the tissue. As the monocyte enters the tissue, it changes (differentiates) into a macrophage. See also: Blood; Cell (biology); Cell biology; Cellular immunology; Immunology; Infection; Pathogen; Phagocytosis

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