What is "macrophage"

macrophage \mac"ro*phage\, n. A large phagocyte.

1890, from macro- + -phage.

n. (context immunology cytology English) A white blood cell that phagocytizes necrotic cell debris and foreign material, including viruses, bacteria, and tattoo ink. It presents foreign antigens on MHC II to lymphocytes. Part of the innate immune system.

n. a large phagocyte; some are fixed and other circulate in the blood stream

Macrophages (, from Greek μακρος (makros) = large, φαγειν (phagein) = to eat) are a type of white blood cell that engulfs and digests cellular debris, foreign substances, microbes, cancer cells, and anything else that does not have the types of proteins specific of healthy body cells on its surface in a process called phagocytosis. These large phagocytes are found in essentially all tissues, where they patrol for potential pathogens by amoeboid movement. They take various forms (with various names) throughout the body (e.g., histiocytes, Kupffer cells, alveolar macrophages, microglia, and others), but all are part of the mononuclear phagocyte system. Besides phagocytosis, they play a critical role in nonspecific defense ( innate immunity) and also help initiate specific defense mechanisms ( adaptive immunity) by recruiting other immune cells such as lymphocytes. For example, they are important as antigen presenters to T cells. In humans, dysfunctional macrophages cause severe diseases such as chronic granulomatous disease that result in frequent infections.

Beyond increasing inflammation and stimulating the immune system, macrophages also play an important anti-inflammatory role and can decrease immune reactions through the release of cytokines. Macrophages that encourage inflammation are called M1 macrophages, whereas those that decrease inflammation and encourage tissue repair are called M2 macrophages. This difference is reflected in their metabolism; M1 macrophages have the unique ability to metabolize arginine to the "killer" molecule nitric oxide, whereas rodent M2 macrophages have the unique ability to metabolize arginine to the "repair" molecule ornithine.

Human macrophages are about in diameter and are produced by the differentiation of monocytes in tissues. They can be identified using flow cytometry or immunohistochemical staining by their specific expression of proteins such as CD14, CD40, CD11b, CD64, F4/80 (mice)/ EMR1 (human), lysozyme M, MAC-1/MAC-3 and CD68.

Macrophages were first discovered by Élie Metchnikoff, a Russian zoologist, in 1884.

The terms "macrophage" and "microphage" are used in ecology to describe heterotrophs that consume food in two different ways. Both macrophages and microphages "ingest solid food and may process it through some sort of alimentary canal." However, a macrophage "handles food items singly, while a microphage handles food items in bulk without manipulating them individually." Microphages include suspension feeders, and often incidentally digest low-quality food items.

Another category of heterotrophs based on feeding mechanism, known as " osmotrophs," is made up of organisms (primarily fungi and bacteria) that absorb organism matter directly across their cell membranes.

The terms "macrophage" and "microphage" were originally used in this sense by Jordan and Hirsch (1927; cited in Yonge 1928). Although they have been used in ecology texts as recently as 2002, the terms macrophage and microphage today are primarily used to describe two different types of white blood cells in the vertebrate immune system.