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Macrophages (abbreviated as Mφ , MΦ or MP ) (Greek: large eaters , from Greek μακρός ( makrós ) = large, φαγεῖν ( phagein ) = to eat) are a type of white blood cell of the immune system that engulfs and digests cellular debris, foreign substances, microbes, cancer cells, and anything else that does not have the type of proteins specific to 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 pre

Types edit A majority of macrophages are stationed at strategic points where microbial invasion or accumulation of foreign particles is likely to occur. These cells together as a group are known as the mononuclear phagocyte system and were previously known as the reticuloendothelial system. Each type of macrophage, determined by its location, has a specific name: Cell Name Anatomical Location Adipose tissue macrophages Adipose tissue (fat) Monocytes Bone marrow / blood Kupffer cells Liver Sinus histiocytes Lymph nodes Alveolar macrophages (dust cells) Pulmonary alveoli Tissue macrophages (histiocytes) leading to giant cells Connective tissue Microglia Central nervous system Hofbauer cells Placenta Intraglomerular mesangial cells Kidney Osteoclasts Bone Epithelioid cells Granulomas Red pulp macrophages (sinusoidal lining cells) Red pulp of spleen Peritoneal macrophages Peritoneal cavity LysoMac Peyer's patch Investigations concerning Kup

Macrophages that reside in adult healthy tissues either derive from circulating monocytes or are established before birth and then maintained during adult life independently of monocytes. By contrast, most of the macrophages that accumulate at diseased sites typically derive from circulating monocytes. When a monocyte enters damaged tissue through the endothelium of a blood vessel, a process known as leukocyte extravasation, it undergoes a series of changes to become a macrophage. Monocytes are attracted to a damaged site by chemical substances through chemotaxis, triggered by a range of stimuli including damaged cells, pathogens and cytokines released by macrophages already at the site. At some sites such as the testis, macrophages have been shown to populate the organ through proliferation. citation needed Unlike short-lived neutrophils, macrophages survive longer in the body, up to several months.

Phagocytosis edit Macrophages are professional phagocytes and are highly specialized in removal of dying or dead cells and cellular debris. This role is important in chronic inflammation, as the early stages of inflammation are dominated by neutrophils, which are ingested by macrophages if they come of age (see CD31 for a description of this process). The neutrophils are at first attracted to a site, where they perform their function and die, before they are phagocytized by the macrophages. When at the site, the first wave of neutrophils, after the process of aging and after the first 48 hours, stimulate the appearance of the macrophages whereby these macrophages will then ingest the aged neutrophils. The removal of dying cells is, to a greater extent, handled by fixed macrophages , which will stay at strategic locations such as the lungs, liver, neural tissue, bone, spleen and connective tissue, ingesting foreign materials such as pathogens and recruiting additional macrophages if nee

Due to their role in phagocytosis, macrophages are involved in many diseases of the immune system. For example, they participate in the formation of granulomas, inflammatory lesions that may be caused by a large number of diseases. Some disorders, mostly rare, of ineffective phagocytosis and macrophage function have been described, for example. As a host for intracellular pathogens edit In their role as a phagocytic immune cell macrophages are responsible for engulfing pathogens to destroy them. Some pathogens subvert this process and instead live inside the macrophage. This provides an environment in which the pathogen is hidden from the immune system and allows it to replicate. Diseases with this type of behaviour include tuberculosis (caused by Mycobacterium tuberculosis ) and leishmaniasis (caused by Leishmania species). In order to minimize the possibility of becoming the host of an intracellular bacteria, macrophages have evolved defense mechanisms such as induction of nitric ox

Though very similar in structure to tissue macrophages, intestinal macrophages have evolved specific characteristics and functions given their natural environment, which is in the digestive tract. Macrophages and intestinal macrophages have high plasticity causing their phenotype to be altered by their environments. Like macrophages, intestinal macrophages are differentiated monocytes, though intestinal macrophages have to coexist with the microbiome in the intestines. This is a challenge considering the bacteria found in the gut are not recognized as "self" and could be potential targets for phagocytosis by the macrophage. To prevent the destruction of the gut bacteria, intestinal macrophages have developed key differences compared to other macrophages. Primarily, intestinal macrophages do not induce inflammatory responses. Whereas tissue macrophages release various inflammatory cytokines, such as IL-1, IL-6 and TNF-α, intestinal macrophages do not produce or secrete inflamm

Play media An active J774 macrophage is seen taking up four conidia in a co-operative manner. The J774 cells were treated with 5 ng/ml interferon-γ one night before filming with conidia. Observations were made every 30s over a 2.5hr period. Play media Two highly active alveolar macrophages can be seen ingesting conidia. Time lapse is 30s per frame over 2.5hr.

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