Their role is to phagocytose (engulf and then digest) cellular debris and pathogens either as stationary or as mobile cells. They also stimulate lymphocytes and other immune cells to respond to the pathogen,
When a monocyte enters damaged tissue through the wall of a blood vessel it changes to become a macrophage. Monocytes are attracted to a damaged site by chemical substances, triggered by a range of stimuli. At some sites such as the testis, macrophages have been shown to populate the organ through proliferation.
Unlike short-lived neutrophils, macrophages survive longer in the body, up to several months.
- Greek: big eaters, from makros "large" + phagein "eat"; abbr. MΦ
- Human macrophages are about 21 micrometres in diameter.Krombach F, Münzing S, Allmeling AM, Gerlach JT, Behr J, Dörger M (1997). "Cell size of alveolar macrophages: an interspecies comparison". Environ. Health Perspect. 105 Suppl 5: 1261–3. doi:10.2307/3433544. PMC 1470168. PMID 9400735. http://jstor.org/stable/3433544.