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Microglia subtype markers

Microglia are the immune effector cells of the central nervous system (CNS) existing in three distinct forms which serve different functional roles. Find out more about these cell types and how to use

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Last edited Mon 29 Apr 2024

Amoeboid microglia

Amoeboid microglia are associated with the developing CNS. In rats, amoeboid microglia have been shown to appear late in gestation and disappear soon after birth

These cells exhibit a round cell body, possess pseudopodia and thin filopodia-like processes and contain numerous lysosomes; all traits indicative of a motile phagocytic phenotype.

During the post-natal period, amoeboid microglia are believed to play a role in tissue histogenesis through the removal of inappropriate and superfluous axons and through the promotion of axonal migration and growth.

Ultimately, amoeboid microglia grow long crenulated processes and transform into ramified microglia found in the adult CNS.

References

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Ramified microglia

Ramified microglia are present in abundance in the brain parenchyma and constitute approximately 10–20% of the total population of glial cells in the adult.

These small round cells comprise numerous branching processes and possess little cytoplasm. In the adult brain, the resident population of ramified microglia is maintained through local cell division and through the recruitment of circulating peripheral blood monocytes.

Under physiological conditions, microglia exhibit pinocytotic activity and localized motility. It has been suggested that ramified microglia contribute to metabolite removal and to the clearance of toxic factors released from injured neurons.

A study has demonstrated that microglia have the propensity to transform into neurons, astrocytes or oligodendrocytes. Hence, ramified microglia may represent a unique population of multipotent stem cells in the adult CNS, which strongly implicates microglia in CNS repair.

References

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Reactive microglia

In response to injury or pathogen invasion, quiescent ramified microglia proliferate and transform into active 'brain macrophages' otherwise known as reactive microglia.

Microglial proliferation can be studied using antibodies raised against nuclear antigens such as Ki67 or proliferating cell nuclear antigen (PCNA) or by bromodeoxyuridine (BrdU) staining.

Reactive microglia are rod-like, devoid of branching processes, and contain numerous lysosomes and phagosomes. The reactive cell form represents a population of macrophages, which are associated with brain injury and neuroinflammation.

Following a damaging event, reactive microglia accumulate at the site of injury where they play a neuroprotective role phagocytosing damaged cells and debris.

In acute lesions the peak of microglial activation occurs 2-3 days post insult, but if the pathological stimulus persists microglial activation continues.

Reactive microglia express MHC class II antigens and other surface molecules necessary for antigen presentation including CD40, B7, and ICAM-1. Consequently, microglia are considered to be the most potent antigen-presenting cells in the CNS. Like macrophages, reactive microglia secrete inflammatory mediators, which orchestrate the cerebral immune response.

Chronic microglial activation is associated with neurological disorders including Alzheimer's disease, multiple sclerosis, and delayed neuronal death occurring after ischaemia.

In these instances, the persistent activation of microglia accompanied by the sustained secretion of inflammatory mediators is thought to have a deleterious effect on neuronal function and survival, thereby exacerbating disease processes.

References

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CD45 - microglia

A paucity of ​specific microglial-only antigens has hindered microglial identification. Markers used for the detection of microglia are also present in macrophage since both cell types exhibit the same lineage.

Microglia are often identified using flow cytometry as it enables to quantify the differences in antigen expression levels. Ramified parenchymal microglia have been demonstrated to possess the phenotype CD11b+, CD45low, whilst other CNS macrophages and peripheral macrophages exhibit the phenotype CD11b+, CD45high.

CD45 expression by microglia (mic) extracted from 5-day old rat neonates. Microglia were isolated and left in culture for 24 hours. The cells were subsequently harvested, fixed, then analyzed by flow cytometry using anti-CD45. Labeled cells are represented by the black shaded populations, whereas the unlabeled cells are depicted by the grey line (%: % of cells in M1 or M2 region, MFI: mean fluorescence intensity).

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References

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CD45 - macrophage

Microglia can also be detected immunologically using antibodies raised against macrophage-specific antigens; however, such antibodies fail to distinguish microglia from macrophages.

CD45 expression by microglia (mic) extracted from 5-day old rat neonates. Microglia were isolated and left in culture for 24 hours. The cells were subsequently harvested, fixed, then analyzed by flow cytometry using anti-CD45. Labeled cells are represented by the black shaded populations, whereas the unlabeled cells are depicted by the grey line.

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CD11b

The OX-42 antibody recognizes the CR3 complement receptor (CD11b/CD18) expressed by rat or mouse microglia. Clone F4/80 binds a 60 kDa glycoprotein on murine ramified microglia.

CD11b expression by microglia (mic) extracted from 5-day old rat neonates. Microglia were isolated and left in culture for 24 hours. The cells were subsequently harvested, fixed, then analyzed by flow cytometry using the OX-42 antibody. Labeled cells are represented by the black shaded populations, whereas unlabeled cells are depicted by the grey line (%: % of cells in M1 or M2 region, MFI: mean fluorescence intensity).​

References

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CD68 - microglia

CD68 is a lysosomal protein and can be used to stain microglia.

CD68 expression by microglia (mic). Cells were extracted from 5-day old rat neonates. Microglia were isolated and left in culture for 24 hours. The cells were subsequently harvested, fixed then analyzed by flow cytometry using anti-CD68 (ED-1) antibodies. Labeled cells are represented by the black shaded populations, whereas the unlabeled cells are depicted by the grey line (%: % of cells in M1 or M2 region, MFI: mean fluorescence intensity).

References

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CD68 - macrophage

High levels of CD68 expression are associated with macrophages and activated microglia, while low levels of expression are associated with quiescent ramified microglia.

Expression of CD68 by peritoneal macrophages.

References

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Silver carbonate staining technique

Identification of microglia can also be achieved using Rio Hortega's original silver carbonate staining technique.

References

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Lectin staining

Lectins are carbohydrate-binding proteins that label microglia through the recognition of glycoproteins containing terminal alpha-D-galactose residues.

References

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Vimentin

Gene names:

VIM

Vimentin is an intermediate filament protein, whose expression is upregulated during the epithelial-to-mesenchymal transition of NE cells to radial glia and persists until astrocyte development.

Rhesus monkey brain tissue sections stained with anti-vimentin (ab92547).

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Low-density lipoprotein

Alternative names:

LDL

Microglia cells can be identified using acetylated low-density lipoprotein (LDL) conjugated to a fluorescent tag, which enables the labeling of LDL receptors.

References

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References

Amoeboid microglia

Dalmau, I., , et al. Development of microglia in the prenatal rat hippocampus. J. Comp. Neurol. 377 ,70-84 (1997)

Innocenti, G.M.,, Clarke, S.,, Koppell, H. Transitory macrophages in the white matter of the developing visual cortex. II. Development and relations with axonal pathways. Dev. Brain Res. 11 ,55-66 (1983)

Kaur, C.,, Ling, E.A. Study of the transformation of amoeboid microglial cells into microglia labelled with the isolectin Griffonia simplicifolia in postnatal rats. Acta. Anat (Basel). 142 ,118-125 (1991)

Ling, E.A. Transformation of monocytes into amoeboid microglia and into microglia in the corpus callosum of postnatal rats, as shown by labelling monocytes by carbon particles. J. Anat. 128 ,847-858 (1979)

Ling E. A.,, Penney D.,, Lebond C. P. Use of carbon labelling to demonstrate the role of blood monocytes as precursors of the ‘amoeboid cells’ present in the corpus collosum of postnatal rats J. Comp. Neurol. 193 ,631-657 (1980)

Marin-Teva, J.L.,, et al. Microglia promote the death of developing purkinje cells. Neuron 41 ,535-547 (2004)

Polazzi, E.,, Contestabile, A. Reciprocal interactions between microglia and neurons: from survival to neuropathology. Rev. Neurosci. 13 ,221-242 (2004)

Ramified microglia

Banati, R. Neuropathological imaging: in vivo detection of glial activation as a measure of disease and adaptive change in the brain. Brit. Med. Bul. 65 ,121-131 (2003)

Booth, P.L.,, Thomas, W.E. Evidence for motility and pinocytosis in ramified microglia in tissue culture. Brain Res. 548 ,163-171 (1991)

Fetler, L.,, Amigorena, S. Brain under surveillance the microglia patrol. Science 309 ,392-393 (2005)

Lawson, L. J.,, Perry, V. H.,, Gordon, S. Turnover of resident microglia in the normal adult mouse brain. Neurosci. 48 ,405-415 (1992)

Thomas, W.E. Brain macrophages: evaluation of microglia and their functions. Brain Res. 17 ,61-74 (1992)

Vaughan, D. W.,, Peters, A. Neuroglial cells in the cerebral cortex of rats from young adult to old age: an electron microscopy study. J. Neurocytol. 3 ,405-429 (1974)

Yokoyama, A.,, Yang, L.,, et al. Microglia, a potent source of neurons, astrocytes and oligodendrocytes. Glia 45 ,96-104 (2004)

Reactive microglia

Kreutzberg, G.W. Microglia: a sensor for pathological events in the CNS. Trends Neurosci 19 ,312-318 (1996)

Stence, N.,, Waite, M.,, Dailey E. Dynamics of microglial-activation: a confocal time-lapse analysis in hippocampal slices. Glia 33 ,256-266 (2001)

Schluter, C.,, Duchrow M.,, et al. The cell proliferation-associated antigen of antibody ki-67: a very large, ubiquitous nuclear protein with numerous repeated elements, representing a new kind of cell cycle maintaining proteins. J. Cell. Biol. 123 ,513-522 (1993)

Bellver-Landete, V.,, Bretheau F.,, et al. Microglia are an essential component of the neuroprotective scar that forms after spinal cord injury. Nat. Commun. 10 (518), (2019)

Tam, W.,, Ma, C. Bipolar/rod-shaped microglia are proliferating microglia with distinct M1/M2 phenotypes. Sci. Rep. 4 (7279), (2015)

Askew, K.,, Kaizhen L.,, et al. Coupled proliferation and apoptosis maintain the rapid turnover of microglia in the adult brain. Cell Rep. 4 ,391-405 (2017)

Kawabori, M.,, Yenari, M.A. The role of the microglia in acute CNS injury. Metab Brain Dis. 30 ,381-392 (2015)

Donat, C.K.,, Scott G.,, et al. Microglial activation in traumatic brain injury. Front Aging Neurosci. 9 , (2017)

Aloisi, F.,, Ria, F.,, et al. Microglia are more efficient than astrocytes in antigen processing and in Th1 but not Th2 cell activation. J. Immunol. 160 ,4671-4680 (1998)

Benveniste, E.N.,, Nguyen, V. T.,, O'Keefe, G.M. Immunological aspects of microglia: relevance to Alzheimer’s disease. Neurochem. Internat. 39 ,381-391 (2001)

Navarro V.,, Sanchez-Mejias E.,, et al. Microglia in Alzheimer's Disease: Activated, Dysfunctional or Degenerative. Front Aging Neurosci. 10 , (2018)

Regen, F.,, Hellmann-Regen, J.,, et al. Neuroinflammation and Alzheimer's disease: implications for microglial activation. Curr Alzheimer Res. 14 ,1140-1148 (2017)

Luo C.,, Chongdong J.,, et al. The role of microglia in multiple sclerosis. Neuropsychiatr. Dis. Treat. 13 ,1661-1667 (2017)

Calabrese, M.,, Magliozzi R.,, et al. Exploring the origins of grey matter damage in multiple sclerosis. Nat Rev Neurosci. 16 ,147-158 (2015)

Tikka T. M.,, Koistinaho J. E. Minocycline provides neuroprotection against N-methyl-D-aspartate neurotoxicity by inhibiting microglia. J. Immunol. (166),7527-7533 (2001)

Lees G.J. The possible contribution of microglia and macrophages to delayed neuronal death after ischaemia. J. Neurol. Sci. 114 ,119-122 (1993)