WordNet

a type of granular leukocyte that functions in the ingestion of bacteria

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/11/09 13:39:00」(JST)

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3D Rendering of a Monocyte

Monocytes are a type of white blood cell.They are the largest of all leucocytes. They are part of the innate immune system of vertebrates including all mammals (humans included), birds, reptiles, and fish. They are amoeboid in shape, having clear cytoplasm. Monocytes have bean-shaped nuclei and constitute 2-10% of all leucocytes in the human body. Monocytes play multiple roles in immune function. Such roles include: (1) replenishing resident macrophages and dendritic cells under normal states, and (2) in response to inflammation signals, monocytes can move quickly (approx. 8–12 hours) to sites of infection in the tissues and divide/differentiate into macrophages and dendritic cells to elicit an immune response. Half of them are stored in the spleen.^[1] Monocytes are usually identified in stained smears by their large kidney shaped or notched nucleus.These change into macrophages after entering into the tissue spaces.

Physiology[edit]

Monocytes are produced by the bone marrow from hematopoietic stem cell precursors called monoblasts. Monocytes circulate in the bloodstream for about one to three days and then typically move into tissues throughout the body. They constitute between three to eight percent of the leukocytes in the blood. Half of them are stored as a reserve in the spleen in clusters in the red pulp's Cords of Billroth.^[1] In the tissues, monocytes mature into different types of macrophages at different anatomical locations. Monocytes are the largest corpuscles in the blood.

Monocytes which migrate from the bloodstream to other tissues will then differentiate into tissue resident macrophages or dendritic cells. Macrophages are responsible for protecting tissues from foreign substances, but are also suspected to be important in the formation of important organs like the heart and brain. They are cells that possess a large smooth nucleus, a large area of cytoplasm, and many internal vesicles for processing foreign material.

Monocytes and their macrophage and dendritic-cell progeny serve three main functions in the immune system. These are phagocytosis, antigen presentation, and cytokine production. Phagocytosis is the process of uptake of microbes and particles followed by digestion and destruction of this material. Monocytes can perform phagocytosis using intermediary (opsonising) proteins such as antibodies or complement that coat the pathogen, as well as by binding to the microbe directly via pattern-recognition receptors that recognize pathogens. Monocytes are also capable of killing infected host cells via antibody, termed antibody-mediated cellular cytotoxicity. Vacuolization may be present in a cell that has recently phagocytized foreign matter.

Microbial fragments that remain after such digestion can serve as antigen. The fragments can be incorporated into MHC molecules and then traffic to the cell surface of monocytes (and macrophages and dendritic cells). This process is called antigen presentation and it leads to activation of T lymphocytes, which then mount a specific immune response against the antigen.

Other microbial products can directly activate monocytes and this leads to production of pro-inflammatory and with some delay of anti-inflammatory cytokines. Typical cytokines produced by monocytes are TNF, IL-1, and IL-12.

Monocyte subpopulations[edit]

There are at least three types of monocytes in human blood:^[2]

a) the classical monocyte is characterized by high level expression of the CD14 cell surface receptor (CD14++ CD16- monocyte)

b) the non-classical monocyte shows low level expression of CD14 and with additional co-expression of the CD16 receptor (CD14+CD16++ monocyte).^[3]

c) the intermediate monocyte with high level expression of CD14 and low level expression of CD16 (CD14++CD16+ monocytes).

There appears to be a developmental relationship in that the classical monocytes develop into the intermediate monocytes to then become the non-classical CD14+CD16++ monocytes. Hence the non-classical monocytes may represent a more mature version. After stimulation with microbial products the CD14+CD16++ monocytes produce high amounts of pro-inflammatory cytokines like tumor necrosis factor and interleukin-12. Said et al. showed that activated monocytes express high levels of PD-1 which might explain the higher expression of PD-1 in CD14+CD16++ monocytes as compared to CD14++CD16- monocytes. Triggering monocytes-expressed PD-1 by its ligand PD-L1 induces IL-10 production which activates CD4 Th2 cells and inhibits CD4 Th1 cell function.^[4]

Diagnostic use[edit]

A scanning electron microscope (SEM) image of normal circulating human blood. One can see red blood cells, several knobby white blood cells including lymphocytes, a monocyte, a neutrophil, and many small disc-shaped platelets.

A monocyte count is part of a complete blood count and is expressed either as a ratio of monocytes to the total number of white blood cells counted, or by absolute numbers. Both may be useful in determining or refuting a possible diagnosis.

Monocytosis[edit]

Monocytosis is the state of excess monocytes in the peripheral blood. It may be indicative of various disease states. Examples of processes that can increase a monocyte count include:

chronic inflammation
stress response
Cushing's syndrome (hyperadrenocorticism)
immune-mediated disease
pyogranulomatous disease
necrosis
red cell regeneration
Viral Fever
sarcoidosis

A high count of CD14+CD16++ monocytes is found in severe infection (sepsis)^[5] and a very low count of these cells is found after therapy with immuno-suppressive glucocorticoids^[6]

Monocytopenia[edit]

Monocytopenia is a form of leukopenia associated with a deficiency of monocytes.

Dendritic cells[edit]

Monocytes can be used to generate dendritic cells in vitro by adding cytokines like Granulocyte Monocyte Colony Stimulating Factor (GMCSF) and IL-4.^[7]

Blood content[edit]

Reference ranges for blood tests of white blood cells, comparing monocyte amount (shown in green) with other cells.

References[edit]

^ ^a ^b Swirski FK, Nahrendorf M, Etzrodt M, Wildgruber M, Cortez-Retamozo V, Panizzi P, Figueiredo J-L, Kohler RH, Chudnovskiy A, Waterman P, Aikawa E, Mempel TR, Libby P, Weissleder R, Pittet MJ. (2009). Identification of Splenic Reservoir Monocytes and Their Deployment to Inflammatory Sites. Science, 325: 612-616. doi:10.1126/science.1175202 PMID 19644120
^ Ziegler-Heitbrock, L et al (2010): Nomenclature of monocytes and dendritic cells in blood. Blood,116 (16): e74-e80. doi:10.1182/blood-2010-02-258558 PMID 20628149
^ Ziegler-Heitbrock, L: The CD14+ CD16+ Blood Monocytes: their Role in Infection and Inflammation, Review. J Leukocyte Biology, 81:584, 2007 doi:10.1189/jlb.0806510 PMID 17135573
^ Elias A. Said et al. 2009, PD-1 Induced IL10 Production by Monocytes Impairs T-cell Activation in a Reversible Fashion. Nature Medicine. 2010; 452-9.
^ Fingerle, G., Pforte, A., Passlick, B., Blumenstein, M., Ströbel, M., Ziegler-Heitbrock, H.W.L.: The novel subset of CD14+ CD16+ blood monocytes is expanded in sepsis patients. Blood, 82: 3170-3176, 1993 PMID 7693040
^ Fingerle-Rowson, G., Angstwurm, M., Andreesen, R., Ziegler-Heitbrock, H.W.L.:Selective depletion of CD14+ CD16+ monocytes by glucocorticoid therapy.Clin. Exp. Immunol., 112: 501-506, 1998 doi:10.1046/j.1365-2249.1998.00617.x PMID 9649222
^ Sallusto F, Cella M, Danieli C, Lanzavecchia A (1995). "Dendritic cells use macropinocytosis and the mannose receptor to concentrate macromolecules in the major histocompatibility complex class II compartment: downregulation by cytokines and bacterial products". J. Exp. Med. 182 (2): 389–400. doi:10.1084/jem.182.2.389. PMC 2192110. PMID 7629501.

External links[edit]

BU Histology Learning System: 01702ooa
Human Monocytes - Prof. Dr. Ziegler-Heitbrock
Circulation of Body Fluids

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English Journal

Palmitate-Stimulated Monocytes Induce Adhesion Molecule Expression in Endothelial Cells via IL-1 Signaling Pathway.

Shikama Y1, Aki N, Hata A, Nishimura M, Oyadomari S, Funaki M.
Journal of cellular physiology.J Cell Physiol.2015 Mar;230(3):732-42. doi: 10.1002/jcp.24797.
Increased intake of saturated fatty acids (SFAs), such as palmitate (Pal), is linked to a higher risk of type 2 diabetes and cardiovascular disease. Although recent studies have investigated the direct effects of SFAs on inflammatory responses in vascular endothelial cells, it remains unknown whethe
PMID 25201247

Fibronectin peptides as potential regulators of hepatic fibrosis through apoptosis of hepatic stellate cells.

Mòdol T1, Brice N, Ruiz de Galarreta M, García Garzón A, Iraburu MJ, Martínez-Irujo JJ, López-Zabalza MJ.
Journal of cellular physiology.J Cell Physiol.2015 Mar;230(3):546-53. doi: 10.1002/jcp.24714.
The turnover of extracellular matrix (ECM) components can generate signals that regulate several cellular functions such as proliferation, differentiation, and apoptosis. During liver injury, matrix metalloproteases (MMPs) production is enhanced and increased levels of peptides derived from extracel
PMID 24976518

Honeybee apisimin and plant arabinogalactans in honey costimulate monocytes.

Gannabathula S1, Krissansen GW2, Skinner M3, Steinhorn G4, Schlothauer R5.
Food chemistry.Food Chem.2015 Feb 1;168:34-40. doi: 10.1016/j.foodchem.2014.07.007. Epub 2014 Jul 9.
Here we determined whether immunostimulatory plant-derived arabinogalactan proteins (AGPs) and the honeybee-derived protein apisimin are present in varieties of New Zealand honey. Apisimin is a protein of unknown function secreted from the glands of honeybees into Royal Jelly, forming a complex with
PMID 25172680

Japanese Journal

Robust and Highly-Efficient Differentiation of Functional Monocytic Cells from Human Pluripotent Stem Cells under Serum- and Feeder Cell-Free Conditions.

Yanagimachi Masakatsu D,Niwa Akira,Tanaka Takayuki,Honda-Ozaki Fumiko,Nishimoto Seiko,Murata Yuuki,Yasumi Takahiro,Ito Jun,Tomida Shota,Oshima Koichi,Asaka Isao,Goto Hiroaki,Heike Toshio,Nakahata Tatsutoshi,Saito Megumu K
PloS one 8(4), 2013-04-03
… Monocytic lineage cells (monocytes, macrophages and dendritic cells) play important roles in immune responses and are involved in various pathological conditions. … This method produced 1.3×10(6)±0.3×10(6) floating monocytes from approximately 30 clusters of ESCs/iPSCs 5-6 times per course of differentiation. … Such monocytes could be differentiated into functional macrophages and dendritic cells. …
NAID 120005244458

A Novel Nrf2-Mediated Antioxidative and Antiinflammatory Mechanism through Ferroportin 1 Induction : A Potential Cytoprotective Mechanism against Ischemia-Reperfusion Injuries

Harada Nobuhiko,Matsuura Shin,Kanayama Masaya,Yoshida Aruto,Itoh Ken
弘前医学 64(Supplement), S74-S80, 2013-04-02
… It is previously reported that LPS suppresses Fpn1 mRNA expression, which leads to iron retention in monocytes and macrophages. …
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Mechanism of Fcγ Receptor-Mediated Trogocytosis-Based False-Positive Results in Flow Cytometry

Masuda Sakiko,Iwasaki Sari,Tomaru Utano,Sato Juri,Kawakami Ai,Ichijo Kana,Sogo Sayuri,Baba Tomohisa,Katsumata Kazuaki,Kasahara Masanori,Ishizu Akihiro
PLoS One 7(12), e52918, 2012-12-27
… Although this method has many virtues, our recent study has demonstrated false-positive results when surface markers of monocytes were examined by this method due to the phenomenon called Fcγ receptor (FcγR)-mediated trogocytosis. … In the present study, similar FcγR-mediated trogocytosis-based false-positive results have been demonstrated when granulocytes were focused on instead of monocytes. …
NAID 120005183187

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