Macrophage (synonym: histiocyte)
Chapter: 2
The most mature form of the mononuclear phagocyte lineage. Its immediate precursor is the monocyte, which is found in the circulation. Macrophages have a wide variety of functions, ranging from the scavenging and degradation of dead tissue and effete cells, through antigen presentation for lymphocytes, to activation for host defense against bacteria, parasites, and tumor cells. The functions of mature macrophages are directed by microenvironmental signals that are encountered by monocytes when they emerge from vessels and begin maturing into macrophages. Your text distinguishes between macrophages and histiocytes, based on prior phagocytic activity (macrophage) of lack thereof (histiocyte). This is an artificial distinction that should not (and is not by most) be used. Macrophages are characteristically found at sites of chronic inflammation and can become specialized in granulomatous inflammatory responses to form epithelioid cells and multinucleated giant cells.