Monocytes and their Markers

Overview

Monocytes are derived from common myeloid progenitors which develop from hematopoietic stem cells in the bone marrow. Monocytes migrate from the bone marrow to circulate in the blood and lymphatic system (Geissmann et al. 2010). In response to various stimuli monocytes can leave the blood and penetrate the surrounding tissue. Within the local tissue environment they can differentiate in to macrophages and some types of dendritic cells (DCs). The cellular fate of monocytes is determined by their exposure to a number of growth factors and cytokines including GM-CSF, IL-4 and M-CSF.

Studies have shown different subtypes of monocytes as discerned by the expression or lack of expression of certain phenotypic markers. The exact role of these different monocyte subtypes (termed as classical and non-classical) is not known, however it’s clear that rather than just being a precursor cell, monocytes have effector functions enabling them to take up pathogens and debris and produce pro-inflammatory mediators (Geissmann et al. 2010). The exact functions of monocytes are likely to be determined by the external stimuli (Auffray et al. 2009). 

For in-depth information regarding monocyte lineage, development and characterisation of monocyte subtypes read the monocyte mini-review.

Monocyte Markers

The exact markers expressed by the monocyte will depend upon the subtype of monocyte and the external stimuli, however monocytes often lack lineage markers for T cells, B cells, NK cells and DC cells, such as: NK1.1, CD90, CD45R and CD11c (Geissmann et al. 2003). The table below shows some of the key monocyte markers for humans and mouse.

Key monocyte markers:

Table constructed using data from Geissmann F et al. 2003.

References:

• Geissmann F. et al. (2003). Blood Monocytes Consist of Two Principal Subsets with Distinct Migratory Properties.
  Immunity. 19:71-82.
• Auffray et al. (2009). Blood monocytes: development, heterogeneity, and relationship with dendritic cells.
  Annu Rev Immunol. 27:669-692.
• Geissmann F et al. (2010). Development of monocytes, macrophages and dendritic cells.
  Science. 327(5966):656-661.