Monocyte

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Monocytes
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Monocyte
blood smear surrounded by red blood cells
Details
SystemImmune system
Identifiers
MeSHD009000
THH2.00.04.1.02010
FMA62864
Anatomical terms of microanatomy]
3D rendering of a monocyte

Monocytes are a type of leukocyte or white blood cell. They are the largest type of leukocyte in blood and can differentiate into macrophages and monocyte-derived dendritic cells. As a part of the vertebrate innate immune system monocytes also influence adaptive immune responses and exert tissue repair functions. There are at least three subclasses of monocytes in human blood based on their phenotypic receptors.

Structure

Monocytes are

peripheral blood.[2][3] Monocytes are mononuclear cells and the ellipsoidal nucleus is often lobulated/indented, causing a bean-shaped or kidney-shaped appearance.[4]
Monocytes compose 2% to 10% of all leukocytes in the human body.

Development

Comparison of monoblast, promonocyte and monocyte.

Monocytes are produced by the

hematopoietic stem cells.[5] Monocytes circulate in the bloodstream for about one to three days and then typically migrate into tissues throughout the body where they differentiate into macrophages and dendritic cells
.

Subpopulations

In humans

The first clear description of monocyte subsets by flow cytometry dates back to the late 1980s, when a population of CD16-positive monocytes was described.[6][7] Today, three types of monocytes are recognized in human blood:[8]

  1. The classical monocyte is characterized by high level expression of the CD14 cell surface receptor (CD14++ CD16− monocyte)
  2. The non-classical monocyte shows low level expression of CD14 and additional co-expression of the CD16 receptor (CD14+CD16++ monocyte).[9]
  3. The intermediate monocyte expresses high levels of CD14 and low levels of CD16 (CD14++CD16+ monocytes).

While in humans the level of CD14 expression can be used to differentiate non-classical and intermediate monocytes, the slan (6-Sulfo LacNAc) cell surface marker was shown to give an unequivocal separation of the two cell types.[10][11]

Ghattas et al. state that the "intermediate" monocyte population is likely to be a unique subpopulation of monocytes, as opposed to a developmental step, due to their comparatively high expression of surface receptors involved in reparative processes (including

Tie-2) as well as evidence that the "intermediate" subset is specifically enriched in the bone marrow.[12]

In mice

In mice, monocytes can be divided in two subpopulations. Inflammatory monocytes (

Ly6Clow, PD-L1pos), which are equivalent to human non-classical CD14+ CD16+ monocytes. Resident monocytes have the ability to patrol along the endothelium wall in the steady state and under inflammatory conditions.[13][14][15][16]

Function

Monocytes are mechanically active cells

antibody-dependent cell-mediated cytotoxicity. Vacuolization
may be present in a cell that has recently phagocytized foreign matter.

Differentiation into other effector cells

Monocytes can migrate into tissues and replenish resident

vesicles for processing foreign material. Although they can be derived from monocytes, a large proportion is already formed prenatally in the yolk sac and foetal liver.[18]

In vitro, monocytes can differentiate into

granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin 4.[19] Such monocyte-derived cells do, however, retain the signature of monocytes in their transcriptome and they cluster with monocytes and not with bona fide dendritic cells.[20]

Specific functions of monocyte subpopulations

Aside from their differentiation capacity, monocytes can also directly regulate immune responses. As explained before, they are able to perform phagocytosis. Cells of the classical subpopulation are the most efficient phagocytes and can additionally secrete inflammation-stimulating factors. The intermediate subpopulation is important for

Th1 cell function.[23]
Many factors produced by other cells can regulate the
N-Formylmethionine leucyl-phenylalanine and other N-formylated oligopeptides which are made by bacteria and activate the formyl peptide receptor 1.[24]
Other microbial products can directly activate monocytes and this leads to production of pro-inflammatory and, with some delay, of anti-inflammatory
IL-12
.

Clinical significance

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 percentage of monocytes among all white blood cells or as absolute numbers. Both may be useful, but these cells became valid diagnostic tools only when monocyte subsets are determined. Monocytic cells may contribute to the severity and disease progression in COVID-19 patients.[25]

Monocytosis

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:

A high count of CD14+CD16++ monocytes is found in severe infection (sepsis).[30]

In the field of atherosclerosis, high numbers of the CD14++CD16+ intermediate monocytes were shown to be predictive of cardiovascular events in populations at risk.[31][32]

CMML is characterized by a persistent monocyte count of > 1000/microL of blood. Analysis of monocyte subsets has demonstrated predominance of classical monocytes and absence of CD14lowCD16+ monocytes.[33][34] The absence of non-classical monocytes can assist in diagnosis of the disease and the use of slan as a marker can improve specificity.[35]

Monocytopenia

Monocytopenia is a form of leukopenia associated with a deficiency of monocytes. A very low count of these cells is found after therapy with immuno-suppressive glucocorticoids.[36]

Also, non-classical slan+ monocytes are strongly reduced in patients with hereditary diffuse leukoencephalopathy with spheroids, a neurologic disease associated with mutations in the macrophage colony-stimulating factor receptor gene.[10]

Blood content

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

See also

Further reading

  • Jakubzick, C. V., Randolph, G. J., & Henson, P. M. (2017). Monocyte differentiation and antigen-presenting functions. In:
    doi:10.1038/nri.2017.28

References

  1. PMID 4107019
    .
  2. ^ Palmer L, Briggs C, McFadden S, et al. ICSH recommendations for the standardization of nomenclature and grading of peripheral blood cell morphological features. Int J Lab Hematol. 2015;37(3):287-303. doi:10.1111/ijlh.12327
  3. ^ Steve, Paxton; Michelle, Peckham; Adele, Knibbs (28 April 2018). "The Leeds Histology Guide". leeds.ac.uk. Archived from the original on 11 October 2017. Retrieved 28 April 2018.
  4. ^ Zini, G. How I investigate difficult cells at the optical microscope. Int J Lab Hematol. 2021; 43: 346– 353. https://doi.org/10.1111/ijlh.13437
  5. PMID 35265979
    .
  6. PMID 2466760
    .
  7. PMID 2478233
    .
  8. S2CID 1570404
    .
  9. S2CID 31534841
    .
  10. ^
    PMID 26443621
    .
  11. PMID 31572354
    .
  12. PMID 23973684
    .
  13. PMID 23582326
    .
  14. S2CID 46067303
    .
  15. PMID 27482114
    .
  16. S2CID 195259881
    .
  17. PMID 34988399
    .
  18. Springer Spektrum, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-56004-4_1
  19. PMID 7629501
    .
  20. PMID 18218067
    .
  21. ^ Wong, K. L. et al. Gene expression profiling reveals the defining features of the classical, intermediate, and nonclassical human monocyte subsets. Blood 118, e16-31, doi:10.1182/blood-2010-12-326355 (2011)
  22. PMID 26085686
    .
  23. PMID 20208540
    .
  24. S2CID 23499393
    .
  25. PMID 32801787
    .
  26. PMID 32316750
    .
  27. PMID 24952646
    .
  28. PMID 17200719
    .
  29. doi:10.1016/j.immuni.2023.03.013. {{cite journal}}: Cite journal requires |journal= (help
    )
  30. PMID 7693040
    .
  31. PMID 18160960
    .
  32. PMID 22999728
    .
  33. S2CID 22571555
    .
  34. PMID 25852055
    .
  35. S2CID 199663779
    .
  36. PMID 9649222
    .

External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Monocyte&oldid=1210338844"