Mononuclear Phagocyte System

Abstract

The mononuclear phagocyte system is part of the innate immune system and comprises dendritic cells (DCs), monocytes and macrophages, which fulfil a range of tasks essential for homeostasis and immunity. Macrophages and DCs were originally thought to be variations of monocytes, but recent evidence has defined the distinct origins of macrophages, monocytes and DCs. Mononuclear phagocytes are functionally specialised and play a critical role in all phases of the immune response. They detect and phagocytose pathogens, recruit cells, initiate adaptive immunity by presenting antigens to T cells and coordinate the resolution of inflammation and wound healing. Macrophages have additional vital functions in tissue development and homeostasis.

Key Concepts

  • Mononuclear phagocytes (dendritic cells, monocytes and macrophages) are a diverse group of cells with a wide range of functions essential for maintaining organism integrity.
  • Macrophages are tissue resident, play a central role in homeostasis, perform tissue‐specific functions and orchestrate immune responses.
  • Dendritic cells are specialised antigen‐presenting cells with superior ability to initiate immune responses.
  • Monocytes are circulating leucocytes that can enter the tissue and have important roles in phagocytosis, inflammation and wound healing.
  • Mononuclear phagocytes coordinate innate and adaptive immune response.

Keywords: macrophage; monocyte; dendritic cell; mononuclear phagocyte; phagocytosis; Kupffer cell; Langerhans cell; osteoclast; microglial cell

Figure 1. Mononuclear phagocyte populations. The self‐maintaining haematopoietic stem cells (HSCs) in the bone marrow give rise to common monocyte progenitors (cMoPs) and common DC precursor (CDP). CDPs differentiate into either conventional (cDC) or plasmacytoid (pDC) dendritic cells. Monocytes can further differentiate into monocyte‐derived cells, macrophages and DCs under certain conditions. Macrophages originally present in tissues have embryonic origin and maintain themselves.
Figure 2. Functional properties of mononuclear phagocyte populations. Abbreviations: cDC, conventional DC; pDC, plasmacytoid DC.
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Further Reading

Biswas SK and Mantovani A (2014) Macrophages: Biology and Role in the Pathology of Diseases. New York: Springer‐Verlag.

Murphy K and Weaver C (2014) Janeway's Immunobiology. New York: Garland Science.

Segura E (2016) Review of mouse and human dendritic cell subsets. In: Segura E and Onai N (eds) Dendritic Cell Protocols, pp. 3–15. New York: Springer.

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Vegh, Peter, Fletcher, James, Dixon, David, and Haniffa, Muzlifah(May 2017) Mononuclear Phagocyte System. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001217.pub2]