Structure




Typesedit

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 Kupffer cells are hampered because in humans, Kupffer cells are only accessible for immunohistochemical analysis from biopsies or autopsies. From rats and mice, they are difficult to isolate, and after purification, only approximately 5 million cells can be obtained from one mouse.

Macrophages can express paracrine functions within organs that are specific to the function of that organ. In the testis, for example, macrophages have been shown to be able to interact with Leydig cells by secreting 25-hydroxycholesterol, an oxysterol that can be converted to testosterone by neighbouring Leydig cells. Also, testicular macrophages may participate in creating an immune privileged environment in the testis, and in mediating infertility during inflammation of the testis.

Cardiac resident macrophages participate in electrical conduction via gap junction communication with cardiac myocytes.

Macrophages can be classified on basis of the fundamental function and activation. According to this grouping there are classically-activated (M1) macrophages, wound-healing macrophages (also known as alternatively-activated (M2) macrophages), and regulatory macrophages (Mregs).

Comments

Post a Comment

Popular posts from this blog

Macrophage

Image
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
Read more

Clinical significance

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
Read more

Function

Image
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
Read more