Editing Monocyte (section)

==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.<ref>{{cite journal |last1=Ziegler-Heitbrock|first1=H W Loems|last2=Passlick |first2=Bernward |last3=Flieger|first3=Dimitri |title= The Monoclonal Antimonocyte Antibody My4 Stains B Lymphocytes and Two Distinct Monocyte Subsets in Human Peripheral Blood. |journal=Hybridoma |date=December 1988 |volume=7 |issue=6 |pages=521–527 |doi= 10.1089/hyb.1988.7.521|pmid= 2466760 }}</ref><ref>{{cite journal |last1=Passlick|first1=Bernward |last2=Flieger|first2=Dimitri |last3= Ziegler-Heitbrock |first3=H W Loems |title= Characterization of a human monocyte subpopulation coexpressing CD14 and CD16 antigens. |journal=Blood |date=November 1989 |volume=74 |issue=7 |pages=2527–2534 |doi= 10.1182/blood.V74.7.2527.2527 |pmid= 2478233 |doi-access=free }}</ref> Today, three types of monocytes are recognized in human blood:<ref>{{cite journal |last1=Ziegler-Heitbrock |first1=Loems |last2=Ancuta |first2=Petronela |last3=Crowe |first3=Suzanne |last4=Dalod |first4=Marc |last5=Grau |first5=Veronika |last6=Hart |first6=Derek N. |last7=Leenen |first7=Pieter J. M. |last8=Liu |first8=Yong-Jun |last9=MacPherson |first9=Gordon |last10=Randolph |first10=Gwendalyn J. |last11=Scherberich |first11=Juergen |last12=Schmitz |first12=Juergen |last13=Shortman |first13=Ken |last14=Sozzani |first14=Silvano |last15=Strobl |first15=Herbert |last16=Zembala |first16=Marek |last17=Austyn |first17=Jonathan M. |last18=Lutz |first18=Manfred B. |title=Nomenclature of monocytes and dendritic cells in blood |journal=Blood |date=21 October 2010 |volume=116 |issue=16 |pages=e74–e80 |doi=10.1182/blood-2010-02-258558 |pmid=20628149 |hdl=11379/41075 |s2cid=1570404 |hdl-access=free }}</ref>
# The classical monocyte is characterized by high level expression of the [[CD14]] cell surface receptor (CD14<sup>++</sup> CD16<sup>−</sup> monocyte)
# The non-classical monocyte shows low level expression of [[CD14]] and additional co-expression of the [[CD16]] receptor (CD14<sup>+</sup>CD16<sup>++</sup> monocyte).<ref>{{cite journal |last1=Ziegler-Heitbrock |first1=Loems |date=March 2007 |title=The CD14+ CD16+ blood monocytes: their role in infection and inflammation |journal=[[Journal of Leukocyte Biology]] |volume=81 |issue=3 |pages=584–592 |doi=10.1189/jlb.0806510 |pmid=17135573 |doi-access=free |s2cid=31534841}}</ref>
# The intermediate monocyte expresses high levels of [[CD14]] and low levels of [[CD16]] (CD14<sup>++</sup>CD16<sup>+</sup> 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.<ref name="ReferenceA">{{cite journal |last1=Hofer |first1=Thomas P. |last2=Zawada |first2=Adam M. |last3=Frankenberger |first3=Marion |last4=Skokann |first4=Kerstin |last5=Satzl |first5=Anna A. |last6=Gesierich |first6=Wolfgang |last7=Schuberth |first7=Madeleine |last8=Levin |first8=Johannes |last9=Danek |first9=Adrian |last10=Rotter |first10=Björn |last11=Heine |first11=Gunnar H. |last12=Ziegler-Heitbrock |first12=Loems |title=slan-defined subsets of CD16-positive monocytes: impact of granulomatous inflammation and M-CSF receptor mutation |journal=Blood |date=10 December 2015 |volume=126 |issue=24 |pages=2601–2610 |doi=10.1182/blood-2015-06-651331 |pmid=26443621 |doi-access=free }}</ref><ref>{{cite journal |last1=Hofer |first1=Thomas P. |last2=van de Loosdrecht |first2=Arjan A. |last3=Stahl-Hennig |first3=Christiane |last4=Cassatella |first4=Marco A. |last5=Ziegler-Heitbrock |first5=Loems |date=13 September 2019 |title=6-Sulfo LacNAc (Slan) as a Marker for Non-classical Monocytes |journal=[[Frontiers in Immunology]] |volume=10 |pages=2052 |doi=10.3389/fimmu.2019.02052 |pmc=6753898 |pmid=31572354 |doi-access=free}}</ref>

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 [[vascular endothelial growth factor]] receptors type 1 and 2, [[CXCR4]], and [[Tie-2]]) as well as evidence that the "intermediate" subset is specifically enriched in the bone marrow.<ref>{{cite journal |last1=Ghattas |first1=Angie |last2=Griffiths |first2=Helen R. |last3=Devitt |first3=Andrew |last4=Lip |first4=Gregory Y.H. |last5=Shantsila |first5=Eduard |date=October 2013 |title=Monocytes in Coronary Artery Disease and Atherosclerosis |journal=[[Journal of the American College of Cardiology]] |volume=62 |issue=17 |pages=1541–1551 |doi=10.1016/j.jacc.2013.07.043 |pmid=23973684 |doi-access=free}}</ref>

===In mice===
In mice, monocytes can be divided in two subpopulations. Inflammatory monocytes ([[CX3CR1]]<sup>low</sup>, [[CCR2]]<sup>pos</sup>, [[Ly6C]]<sup>high</sup>, [[PD-L1]]<sup>neg</sup>), which are equivalent to human classical CD14<sup>++</sup> CD16<sup>−</sup> monocytes and resident monocytes ([[CX3CR1]]<sup>high</sup>, [[CCR2]]<sup>neg</sup>, [[Ly6C]]<sup>low</sup>, [[PD-L1]]<sup>pos</sup>), which are equivalent to human non-classical CD14<sup>+</sup> CD16<sup>+</sup> monocytes. Resident monocytes have the ability to patrol along the endothelium wall in the steady state and under inflammatory conditions.<ref>{{cite journal |last1=Carlin |first1=Leo M. |last2=Stamatiades |first2=Efstathios G. |last3=Auffray |first3=Cedric |last4=Hanna |first4=Richard N. |last5=Glover |first5=Leanne |last6=Vizcay-Barrena |first6=Gema |last7=Hedrick |first7=Catherine C. |last8=Cook |first8=H. Terence |last9=Diebold |first9=Sandra |last10=Geissmann |first10=Frederic |title=Nr4a1-Dependent Ly6Clow Monocytes Monitor Endothelial Cells and Orchestrate Their Disposal |journal=Cell |date=April 2013 |volume=153 |issue=2 |pages=362–375 |doi=10.1016/j.cell.2013.03.010 |pmid=23582326 |pmc=3898614 }}</ref><ref>{{cite journal |last1=Auffray |first1=Cedric |last2=Fogg |first2=Darin |last3=Garfa |first3=Meriem |last4=Elain |first4=Gaelle |last5=Join-Lambert |first5=Olivier |last6=Kayal |first6=Samer |last7=Sarnacki |first7=Sabine |last8=Cumano |first8=Ana |last9=Lauvau |first9=Gregoire |last10=Geissmann |first10=Frederic |title=Monitoring of Blood Vessels and Tissues by a Population of Monocytes with Patrolling Behavior |journal=Science |date=3 August 2007 |volume=317 |issue=5838 |pages=666–670 |doi=10.1126/science.1142883 |pmid=17673663 |bibcode=2007Sci...317..666A |s2cid=46067303 }}</ref><ref>{{cite journal |last1=Imhof |first1=Beat A. |last2=Jemelin |first2=Stephane |last3=Ballet |first3=Romain |last4=Vesin |first4=Christian |last5=Schapira |first5=Marc |last6=Karaca |first6=Melis |last7=Emre |first7=Yalin |date=16 August 2016 |title=CCN1/CYR61-mediated meticulous patrolling by Ly6C low monocytes fuels vascular inflammation |journal=[[Proceedings of the National Academy of Sciences]] |volume=113 |issue=33 |pages=E4847–E4856 |doi=10.1073/pnas.1607710113 |pmc=4995973 |pmid=27482114 |bibcode=2016PNAS..113E4847I |doi-access=free}}</ref><ref>{{cite journal |last1=Bianchini |first1=Mariaelvy |last2=Duchêne |first2=Johan |last3=Santovito |first3=Donato |last4=Schloss |first4=Maximilian J. |last5=Evrard |first5=Maximilien |last6=Winkels |first6=Holger |last7=Aslani |first7=Maria |last8=Mohanta |first8=Sarajo K. |last9=Horckmans |first9=Michael |last10=Blanchet |first10=Xavier |last11=Lacy |first11=Michael |date=21 June 2019 |title=PD-L1 expression on nonclassical monocytes reveals their origin and immunoregulatory function |journal=[[Science Immunology]] |volume=4 |issue=36 |pages=eaar3054 |doi=10.1126/sciimmunol.aar3054 |pmid=31227596 |doi-access=free |last12=von Hundelshausen |first12=Philipp |last13=Atzler |first13=Dorothee |last14=Habenicht |first14=Andreas |last15=Gerdes |first15=Norbert |last16=Pelisek |first16=Jaroslav |last17=Ng |first17=Lai Guan |last18=Steffens |first18=Sabine |last19=Weber |first19=Christian |last20=Megens |first20=Remco T. A. |s2cid=195259881}}</ref>