Macrophage

A type of white blood that ingests (takes in) foreign material. Macrophages are key players in the immune response to foreign invaders such as infectious microorganisms. Blood monocytes migrate into the tissues of the body and there differentiate (evolve) into macrophages. Macrophages help destroy bacteria, protozoa, and tumor cells. They also release substances that stimulate other cells of the immune system. And they are involved in antigen presentation. To do this, they carry the antigen on their surface and present it to a T cells.

* * *

Any mononuclear, actively phagocytic cell arising from monocytic stem cells in the bone marrow; these cells are widely distributed in the body and vary in morphology and motility, though most are large, long-lived cells with a nearly round nucleus and have abundant endocytic vacuoles, lysosomes, and phagolysosomes. Phagocytic activity is typically mediated by serum recognition factors, including certain immunoglobulins and components of the complement system, but also may be nonspecific for some inert materials and bacteria, as in the case of alveolar macrophages; macrophages also are involved in both the production of antibodies and in cell-mediated immune responses, participate in presenting antigens to lymphocytes, and secrete a variety of immunoregulatory molecules. SYN: macrophagocyte, rhagiocrine cell. [macro- + G. phago, to eat]

- activated m. a mature m., in an active metabolic state, that is cytotoxic to tumor/target cells, usually following exposure to certain cytokines. SYN: armed m..

- alveolar m. a vigorously phagocytic m. on the epithelial surface of lung alveoli where it ingests inhaled particulate matter. SYN: coniophage, dust cell.

- armed m. SYN: activated m..

- fixed m. a relatively immotile m. found in connective tissue, lymph node s, spleen, and bone marrow. SYN: resting wandering cell.

- free m. an actively motile m. typically found in sites of inflammation.

- Hansemann m. obsolete term for large histiocytes with abundant cytoplasm that may contain Michaelis-Gutmann bodies and one or several nuclei; described in lesions of malacoplakia.

- inflammatory m. a m. found at sites of inflammation.

- tangible body m. a m. that specializes in phagocytosis of lymphoid cells.

* * *

mac·ro·phage 'mak-rə-.fāj, -.fäzh n a phagocytic tissue cell of the immune system that may be fixed or freely motile, is derived from a monocyte, functions in the destruction of foreign antigens (as bacteria and viruses), and serves as an antigen-presenting cell see HISTIOCYTE, mononuclear phagocyte system

mac·ro·phag·ic .mak-rə-'faj-ik adj

* * *

n.

a large scavenger cell (a phagocyte) present in connective tissue and many major organs and tissues, including the bone marrow, spleen, lymph node, liver (see Kupffer cells), and the central nervous system (see microglia). They are closely related to monocyte. Fixed macrophages (histiocytes) are stationary within connective tissue; free macrophages wander between cells and aggregate at focal sites of infection, where they remove bacteria or other foreign bodies from blood or tissues. See also reticuloendothelial system.

* * *

mac·ro·phage (makґro-fāj″) [macro- + -phage] any of the many forms of mononuclear phagocytes found in tissues. They arise from hematopoietic stem cells in the bone marrow, which develop according to the stages of the monocytic series until they are monocytes; these then enter the blood, circulate for about 40 hours, and subsequently enter tissues, where they increase in size, phagocytic activity, and lysosomal enzyme content to become macrophages. Two types, fixed macrophages and free macrophages (qq.v.) are distinguished. Their morphology varies among different tissues and between normal and pathologic states, and not all macrophages can be identified by morphology alone. However, most are large cells with a round or indented nucleus, a well-developed Golgi apparatus, abundant endocytotic vacuoles, lysosomes, and phagolysosomes, and a plasma membrane covered with ruffles or microvilli. Their functions include nonspecific phagocytosis and pinocytosis, specific phagocytosis of opsonized microorganisms (mediated by Fc receptors and complement receptors); killing of ingested microorganisms; digestion and presentation of antigens to T and B lymphocytes; and secretion of many different products, including enzymes (lysozyme, collagenases, elastase), acid hydrolases, several complement components and coagulation factors, prostaglandins and leukotrienes, and regulatory molecules such as interferon and interleukin-1. Cells now recognized as macrophages include (in normal tissue) interdigitating cells, Kupffer cells, Langerhans cells, microglial cells, osteoclasts, and type A synovial cells, and (in inflamed tissues) epithelioid cells and Langerhans-type and foreign-body–type giant cells. Called also histiocyte and macrophagocyte.