Monocyte

Monocytes, and monocytes ( from Ancient Greek μόνος monos "alone", " only ", and ancient Greek κύτος CYTOS " cavity ", " vessel ", "shell" ), are circulating in the blood cells of the immune system and the forerunner of, inter alia, in the localized tissue macrophages as well as a portion of the dendritic cells. Your task is to destroy exogenous structures by phagocytosis and the activation of the acquired immune response via antigen presentation. The most important location for monocytes is the spleen. The monocytes are common to both specific and non-specific defense system to. Circulating monocytes have a lifespan 1-3 days prior to the differentiation and migrate into the tissues. There they live as macrophages for several more weeks to months.

Construction

With a diameter of 5-20 microns are monocytes to the largest of the white blood cells ( leukocytes) and account for about 3-8 % of the leukocyte population of. They have a characteristic (from the Greek monos, "one " ) large core of mostly bean- like shape and relatively little cytoplasm. Monocytes are not a homogeneous cell population, but are made between various subpopulations. In addition to the typical monocyte surface marker CD14, there are subpopulations, which additionally carry the marker CD16. CD14 CD16 monocytes are predictors of future cardiovascular events in dialysis patients, in patients with chronic kidney disease not on dialysis and in patients with coronary heart disease. Since no surface markers have been known, which is exclusively expressed on monocytes, combinations of surface markers to be used to identify uniquely the monocytes by flow cytometry.

Since 2010, an international consensus to distinguish three subpopulations of monocytes is:

• Classical monocytes (CD14 CD16 - )
• Intermediate monocyts (CD14 CD16 )
• Non -classical monocytes (CD14 CD16 )

Values ​​used in the identification of surface markers on monocytes of other mammals differ partly from those of humans. When rats are ED9, CD43 and CD62, CD163 used for pigs.

Development and function

In the bone marrow contained hematopoietic ( blood-forming ) stem cells can develop under the influence of certain growth factors such as GM- CSF ( granulocyte-macrophage colony - stimulating factor) and M -CSF ( macrophage colony - stimulating factor) in so-called monoblasts. Develop from them again ( " differentiated " ) merge to monocytes, which thereby leave the bone marrow and into the bloodstream. There they circulate for 1-3 days. Within this period, they migrate in contact with infection in the affected tissue. This ability monocytes have in common with neutrophils, however, take time lag (up to several days ) at the infection site a ( more detailed description: see neutrophilic granulocyte ). The main location of the monocyte is the red pulp of the spleen, from which they can be released during acute inflammation in large numbers. During the migration into the tissue itself monocytes differentiate into macrophages. Before differentiation into macrophage monocytes are able to take up exogenous intracellular structures such as micro-organisms and to destroy. Thus monocytes are capable of antigen presentation and initiating in this way the acquired immune response.

Monocytes can be stimulated in vitro with certain cytokines and differentiated into dendritic cells or macrophages.

Vesicles composed of membrane fragments of monocytes can form so-called circulating in the blood microparticles containing, inter alia, tissue factor ( engl. tissue factor ). This is mainly involved in the process of blood clotting.

Cell signaling

Components of bacterial cell walls, bacterial lipoproteins or antigen- bound antibodies activate certain " toll-like " receptors ( TLRs ), which are found on the plasma membrane of monocytes, macrophages and B cells. The activation of TLR2 and TLR4 is conducted via signal transduction into the cell interior. As a result, for example, inflammatory substances (mediators such as interleukin- 1β, interleukin-6 or tumor necrosis factor ) can be produced or introduced phagocytosis process.

Monocyte -associated diseases

Monocytes and macrophages process in natural dimensions LDL, an important part of fat metabolism. Is this, however, modified by acetylation of the protein fraction, this oxidized LDL can not be processed and accumulates in the cell interior. The resulting macrophages known as foam cells. They are related to injured blood vessels as the main cause of atherosclerosis.

An increase in monocyte number as a result of chronic inflammation or necrosis is called monocytosis.

Immunophenotype

Table is contained in the original with References for all items in PMID 22416241 (OA ).