Microglial Polarization is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
Microglial polarization refers to the process by which [microglia[/entities/microglia/[diseases[/entities/microglia/[diseases[/entities/microglia/[diseases--TEMP--/entities/microglia)--FIX--, including [Alzheimer's disease[/diseases/[alzheimers[/diseases/[alzheimers[/diseases/[alzheimers--TEMP--/diseases)--FIX--, [Parkinson's disease[/diseases/[parkinsons[/diseases/[parkinsons[/diseases/[parkinsons--TEMP--/diseases)--FIX--, [ALS[/diseases/[als[/diseases/[als[/diseases/[als--TEMP--/diseases)--FIX--, [Huntington's disease[/mechanisms/[huntington-pathway[/mechanisms/[huntington-pathway[/mechanisms/[huntington-pathway--TEMP--/mechanisms)--FIX--, and [multiple sclerosis[/diseases/[multiple-sclerosis[/diseases/[multiple-sclerosis[/diseases/[multiple-sclerosis--TEMP--/diseases)--FIX--, making it a major therapeutic target (Cheng et al., 2025).
The study of Microglial Polarization has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
M1-polarized [microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX-- including aggregated [amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta--TEMP--/entities)--FIX-- and [alpha-synuclein[/proteins/[alpha-synuclein[/proteins/[alpha-synuclein[/proteins/[alpha-synuclein--TEMP--/proteins)--FIX-- (Shaul et al., 2017)):
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Pro-inflammatory cytokine release: TNF-α, IL-1β, IL-6, IL-12, IL-23
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Reactive oxygen and nitrogen species: Production of superoxide, nitric oxide (via iNOS), and peroxynitrite, contributing to oxidative stress
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Chemokine secretion: CCL2, CXCL10 attracting [peripheral immune cells]
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Reduced phagocytic efficiency: Paradoxically, while M1 [microglia (Cherry et al., 2014:
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M2a (alternative activation): Induced by IL-4/IL-13; promotes tissue repair and phagocytosis
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M2b (type II activation): Regulatory phenotype with both pro- and anti-inflammatory features
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M2c (acquired deactivation): Induced by IL-10/TGF-β; promotes matrix remodeling and debris clearance
Common M2 characteristics:
- Anti-inflammatory cytokine release: IL-10, TGF-β, IL-4
- Neurotrophic factor production: BDNF, GDNF, IGF-1
- Enhanced phagocytosis: Efficient clearance of [amyloid] plaques, dead cells, and debris
- Tissue repair: Promotion of [neurogenesis[/entities/[neurogenesis[/entities/[neurogenesis[/entities/[neurogenesis--TEMP--/entities)--FIX--, remyelination, and extracellular matrix remodeling
- Resolution of inflammation: Active termination of inflammatory cascades
Key transcription factors: STAT6, STAT3, PPARγ, IRF4
Surface markers: CD206 (mannose receptor), Arg1 (arginase-1), Ym1, FIZZ1, CD163
While the M1/M2 framework provides a useful conceptual foundation, it has significant limitations that have been recognized through advanced transcriptomic profiling Ransohoff, 2016:
- Oversimplification: [microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX-- rarely adopt pure M1 or M2 states in vivo; they display mixed and intermediate phenotypes with unique gene expression profiles
- Context dependency: The same stimulus can elicit different responses depending on the microenvironment, disease stage, and brain region
- Temporal dynamics: [Microglia continuously shift phenotypes over time, not maintaining stable states (Masuda et al., 2019
- In vivo complexity: M1/M2 markers defined in vitro often do not translate to in vivo microglial populations
- Species differences: Mouse M1/M2 markers do not always correspond to human microglial states (Orihuela et al., 2016)
Single-cell RNA sequencing has revealed [disease-associated microglia (DAM)[/cell-types/[neuroinflammation-microglia[/cell-types/[neuroinflammation-microglia[/cell-types/[neuroinflammation-microglia--TEMP--/cell-types)--FIX-- as a specialized microglial state that emerges in neurodegeneration Keren-Shaul et al., 2017). DAM are characterized by:
- Downregulation of homeostatic genes: P2ry12, Tmem119, Cx3cr1
- Upregulation of activation genes: [TREM2[/genes/[trem2[/genes/[trem2[/genes/[trem2--TEMP--/genes)--FIX--, Apoe, Lpl, Cst7, Spp1
- Two-stage activation:
- Stage 1 ([TREM2[/genes/[trem2[/genes/[trem2[/genes/[trem2--TEMP--/genes)--FIX--: Initial response with moderate transcriptional changes
- Stage 2 ([TREM2[/genes/[trem2[/genes/[trem2[/genes/[trem2--TEMP--/genes)--FIX--: Full DAM phenotype requiring [TREM2[/genes/[trem2[/genes/[trem2[/genes/[trem2--TEMP--/genes)--FIX-- signaling, with enhanced phagocytosis and lipid metabolism
- Enhanced lipid metabolism and phagocytic capacity
- Presence across neurodegenerative diseases: Originally identified in AD mouse models, DAM signatures are found in [ALS[/diseases/[als[/diseases/[als[/diseases/[als--TEMP--/diseases)--FIX--, [Parkinson's disease[/diseases/[parkinsons[/diseases/[parkinsons[/diseases/[parkinsons--TEMP--/diseases)--FIX--, aging, and other conditions
The DAM phenotype does not neatly fit M1 or M2 categories — it combines elements of both activation and neuroprotection, supporting the continuum model.
Large-scale single-cell profiling has identified multiple microglial subsets beyond DAM Masuda et al., 2019):
| State |
Key Markers |
Function |
Disease Context |
| Homeostatic |
P2ry12, Tmem119, Cx3cr1 |
Surveillance, synaptic pruning |
Healthy brain |
| [DAM, aging |
|
|
|
| Lipid-droplet-accumulating (LDAM) |
PLIN2, LPL |
Lipid storage, reduced phagocytosis |
Aging, AD |
A critical determinant of microglial polarization state is cellular metabolism. Metabolic reprogramming drives and sustains different functional phenotypes Cheng et al., 2025 (Microglia et al., 2022):
- Glycolytic shift: Pro-inflammatory activation switches [microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX--**: Anti-inflammatory [microglia[/entities/[microglia[/entities/[microglia[/entities/[microglia--TEMP--/entities)--FIX-- rely on mitochondrial oxidative metabolism
- Fatty acid oxidation (FAO): β-oxidation of fatty acids provides sustained ATP for phagocytosis and tissue repair
- AMPK activation: AMP-activated protein kinase promotes FAO and suppresses [NF-κB[/entities/[nf-kb[/entities/[nf-kb[/entities/[nf-kb--TEMP--/entities)--FIX---driven inflammation
- PPARγ signaling: Peroxisome proliferator-activated receptor gamma drives anti-inflammatory gene programs and lipid metabolism
- Arginase pathway: Arginine metabolism shifts from iNOS (M1) to arginase (M2), producing polyamines for tissue repair
A key pathological feature in neurodegenerative diseases is the inability of microglia to efficiently transition between metabolic states. This "metabolic inflexibility" leads to:
- Chronic reliance on glycolysis with sustained pro-inflammatory output
- Impaired phagocytic function despite activation (energy-dependent process)
- Accumulation of lipid droplets (lipid-droplet-accumulating microglia, LDAM) due to impaired lipid catabolism
- Progressive loss of neuroprotective capacity over disease course
- [NF-κB[/entities/[nf-kb[/entities/[nf-kb[/entities/[nf-kb--TEMP--/entities)--FIX-- pathway: Central transcription factor for M1 genes; activated by [TLR4[/entities/[tlr4[/entities/[tlr4[/entities/[tlr4--TEMP--/entities)--FIX--, TNF receptors, and [NLRP3[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome--TEMP--/mechanisms)--FIX-- inflammasome]
- JAK-STAT1 axis: IFN-γ signaling through STAT1 drives M1 gene expression (iNOS, MHCII)
- MAPK cascades: p38, ERK, and JNK pathways amplify inflammatory signaling
- [NLRP3[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome--TEMP--/mechanisms)--FIX-- inflammasome]: Assembles in response to DAMPs; drives IL-1β and IL-18 maturation via [caspase]-1 activation, promoting [pyroptosis[/mechanisms/[pyroptosis[/mechanisms/[pyroptosis[/mechanisms/[pyroptosis--TEMP--/mechanisms)--FIX--
- [STING[/entities/[sting-pathway[/entities/[sting-pathway[/entities/[sting-pathway--TEMP--/entities)--FIX-- pathway]: Cytosolic DNA sensing activates type I interferon responses
- HMGB1-[RAGE[/proteins/[rage[/proteins/[rage[/proteins/[rage--TEMP--/proteins)--FIX-- axis: High-mobility group box 1 protein binding to [RAGE[/proteins/[rage[/proteins/[rage[/proteins/[rage--TEMP--/proteins)--FIX-- receptor] promotes pro-inflammatory polarization
- [TREM2[/genes/[trem2[/genes/[trem2[/genes/[trem2--TEMP--/genes)--FIX-- signaling: Triggering receptor expressed on myeloid cells 2 promotes DAM phenotype, enhances phagocytosis and metabolic fitness via PLCγ2
- PPARγ activation: Nuclear receptor that antagonizes [NF-κB[/entities/[nf-kb[/entities/[nf-kb[/entities/[nf-kb--TEMP--/entities)--FIX-- and promotes anti-inflammatory gene expression
- IL-4/IL-13–STAT6 axis: Canonical M2 induction pathway
- AMPK/[mTOR[/mechanisms/[mtor-neurodegeneration[/mechanisms/[mtor-neurodegeneration[/mechanisms/[mtor-neurodegeneration--TEMP--/mechanisms)--FIX-- axis: AMPK suppresses [mTOR[/mechanisms/[mtor-neurodegeneration[/mechanisms/[mtor-neurodegeneration[/mechanisms/[mtor-neurodegeneration--TEMP--/mechanisms)--FIX---driven glycolysis, favoring OXPHOS and anti-inflammatory phenotype
- TGF-β/SMAD signaling: Promotes microglial quiescence and homeostatic functions
- Wnt/β-catenin pathway: Supports microglial homeostasis and anti-inflammatory responses
- CD200-CD200R axis: Neuronal CD200 engagement of microglial CD200R maintains quiescent state
In [Alzheimer's disease[/diseases/[alzheimers[/diseases/[alzheimers[/diseases/[alzheimers--TEMP--/diseases)--FIX--, microglial polarization evolves over disease stages Wang et al., 2015):
- Early disease: [Microglia/microglial phagocytosis). [TREM2[/genes/[trem2[/genes/[trem2[/genes/[trem2--TEMP--/genes)--FIX---dependent DAM cluster around plaques.
- Disease progression: Chronic exposure to [Aβ[/entities/[amyloid-beta[/entities/[amyloid-beta[/entities/[amyloid-beta--TEMP--/entities)--FIX-- and tau] aggregates drives a shift toward pro-inflammatory states. [NF-κB[/entities/[nf-kb[/entities/[nf-kb[/entities/[nf-kb--TEMP--/entities)--FIX-- and [NLRP3[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome--TEMP--/mechanisms)--FIX-- inflammasome activation dominate.
- Late disease: [microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX-- become dystrophic with impaired phagocytosis, metabolic dysfunction, and [cellular senescence[/mechanisms/[cellular-senescence[/mechanisms/[cellular-senescence[/mechanisms/[cellular-senescence--TEMP--/mechanisms)--FIX--. They release neurotoxic factors without effectively clearing pathology.
Key findings:
- HK2 deficiency paradoxically enhances amyloid clearance by shifting microglia to lipid-derived ATP production
- Histone H4 lactylation creates a positive feedback loop amplifying glycolysis and inflammatory gene expression
- Reduced [TREM2[/genes/[trem2[/genes/[trem2[/genes/[trem2--TEMP--/genes)--FIX-- signaling compromises metabolic fitness and phagocytic capacity
- [Complement-mediated synapse loss[/mechanisms/[complement-mediated-synapse-loss[/mechanisms/[complement-mediated-synapse-loss[/mechanisms/[complement-mediated-synapse-loss--TEMP--/mechanisms)--FIX-- is driven by M1-polarized microglia
In [Parkinson's disease[/diseases/[parkinsons[/diseases/[parkinsons[/diseases/[parkinsons--TEMP--/diseases)--FIX-- Tang & Le, 2016):
- [alpha-synuclein[/proteins/[alpha-synuclein[/proteins/[alpha-synuclein[/proteins/[alpha-synuclein--TEMP--/proteins)--FIX-- and TLR2, driving glycolytic reprogramming and pro-inflammatory activation
- [Inflammasome] activation in response to α-synuclein fibrils promotes IL-1β release
- Iron dysregulation in the substantia nigra exacerbates oxidative stress and M1 polarization
- [LRRK2[/genes/[lrrk2[/genes/[lrrk2[/genes/[lrrk2--TEMP--/genes)--FIX-- mutations affect microglial inflammatory responses and polarization dynamics
- DJ-1 deficiency impairs anti-inflammatory microglial function
In [ALS[/diseases/[als[/diseases/[als[/diseases/[als--TEMP--/diseases)--FIX--:
- Early disease stages show M2-dominant microglial responses that are neuroprotective
- As disease progresses, a dramatic shift to M1 polarization occurs, accelerating [motor neuron] degeneration
- [SOD1/proteins/sod1 mutations drive microglial inflammatory activation
- [TDP-43[/entities/[tdp-43[/entities/[tdp-43[/entities/[tdp-43--TEMP--/entities)--FIX-- pathology affects microglial function through altered RNA metabolism
- [C9orf72[/genes/[c9orf72[/genes/[c9orf72[/genes/[c9orf72--TEMP--/genes)--FIX-- repeat expansions cause microglial dysfunction and abnormal inflammatory responses
In [MS]:
- M1 microglia contribute to [demyelination[/mechanisms/[demyelination[/mechanisms/[demyelination[/mechanisms/[demyelination--TEMP--/mechanisms)--FIX-- through release of inflammatory mediators and reactive oxygen species
- M2 microglia promote remyelination by clearing myelin debris and releasing growth factors
- White matter-associated microglia represent a specialized population involved in myelin homeostasis
- The balance between M1 and M2 states determines disease relapse vs. remission phases
In [Huntington's disease[/mechanisms/[huntington-pathway[/mechanisms/[huntington-pathway[/mechanisms/[huntington-pathway--TEMP--/mechanisms)--FIX--:
- Mutant [huntingtin[/proteins/[huntingtin[/proteins/[huntingtin[/proteins/[huntingtin--TEMP--/proteins)--FIX-- protein] causes cell-autonomous microglial activation
- Activated microglia appear years before symptom onset
- Both pro-inflammatory and anti-inflammatory pathways are dysregulated
- [Kynurenine pathway[/mechanisms/[kynurenine-pathway[/mechanisms/[kynurenine-pathway[/mechanisms/[kynurenine-pathway--TEMP--/mechanisms)--FIX-- metabolites from activated microglia contribute to excitotoxicity
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PPARγ agonists: Pioglitazone and rosiglitazone shift microglia toward M2 phenotype; clinical trials in AD have shown mixed results but biomarker improvements Mandrekar-Colucci et al., 2012
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AMPK activators: Metformin and AICAR suppress glycolytic inflammatory activation and promote anti-inflammatory metabolism
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[mTOR[/mechanisms/[mtor-neurodegeneration[/mechanisms/[mtor-neurodegeneration[/mechanisms/[mtor-neurodegeneration--TEMP--/mechanisms)--FIX-- inhibitors: Rapamycin reduces inflammatory signaling and promotes autophagy, shifting microglial phenotype
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[TREM2[/genes/[trem2[/genes/[trem2[/genes/[trem2--TEMP--/genes)--FIX-- agonists: Antibodies and small molecules that enhance [TREM2[/genes/[trem2[/genes/[trem2[/genes/[trem2--TEMP--/genes)--FIX-- signaling promote DAM transition and phagocytic function; multiple candidates in clinical development
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[NLRP3[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome--TEMP--/mechanisms)--FIX-- inhibitors: MCC950 and other [NLRP3[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome[/mechanisms/[nlrp3-inflammasome--TEMP--/mechanisms)--FIX-- inflammasome inhibitors reduce IL-1β-driven neuroinflammation [4]
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JAK inhibitors: Baricitinib and tofacitinib reduce STAT1-mediated M1 polarization; being investigated in neuroinflammatory conditions
-
P2X7 receptor antagonists: Block purinergic signaling that drives microglial activation and inflammasome assembly
Several natural compounds modulate microglial polarization:
- Resveratrol: Activates PGC-1α and SIRT1, promoting anti-inflammatory phenotype
- Curcumin: Inhibits [NF-κB[/entities/[nf-kb[/entities/[nf-kb[/entities/[nf-kb--TEMP--/entities)--FIX-- and promotes PPARγ activity
- Quercetin: Shifts microglial phenotype by suppressing M1 markers
- Cyanidin-3-O-glucoside: Regulates M1/M2 balance via PPARγ pathway
- Omega-3 fatty acids: DHA and EPA promote resolution of inflammation
- [Vagus nerve stimulation[/treatments/[vagus-nerve-stimulation[/treatments/[vagus-nerve-stimulation[/treatments/[vagus-nerve-stimulation--TEMP--/treatments)--FIX--: Activates the cholinergic anti-inflammatory pathway, shifting microglia from M1 to M2 phenotype via α7 nicotinic receptor signaling
- [Transcranial magnetic stimulation[/treatments/[transcranial-magnetic-stimulation[/treatments/[transcranial-magnetic-stimulation[/treatments/[transcranial-magnetic-stimulation--TEMP--/treatments)--FIX--: Modulates microglial activation state in targeted brain regions
- [Deep brain stimulation[/treatments/[deep-brain-stimulation[/treatments/[deep-brain-stimulation[/treatments/[deep-brain-stimulation--TEMP--/treatments)--FIX--: May influence local microglial phenotype through electrical modulation
- Metabolic reprogramming: Targeting microglial metabolism to restore metabolic flexibility — e.g., ketogenic diet approaches that alter microglial lipid profiles and morphology Cheng et al., 2025
- [Nanomedicine[/[treatments[/[treatments[/[treatments[/treatments: Nanoparticle-based drug delivery systems targeting microglia for polarization modulation
- Gene therapy: [CRISPR[/treatments/[crispr-gene-editing[/treatments/[crispr-gene-editing[/treatments/[crispr-gene-editing--TEMP--/treatments)--FIX---based approaches to modify microglial gene expression
- CAR-microglia: Engineered chimeric antigen receptor microglia for targeted clearance of pathological proteins
- Exosome-based therapy: [Extracellular vesicles[/mechanisms/[extracellular-vesicles[/mechanisms/[extracellular-vesicles[/mechanisms/[extracellular-vesicles--TEMP--/mechanisms)--FIX-- loaded with anti-inflammatory cargo to reprogram microglial phenotype
- Primary microglial cultures: From mouse brain tissue; stimulated with LPS/IFN-γ (M1) or IL-4/IL-13 (M2)
- BV-2 and HMC3 cell lines: Immortalized microglial cell lines for high-throughput screening
- iPSC-derived microglia: Human patient-derived microglia-like cells for disease modeling
- Single-cell RNA sequencing (scRNA-seq): Gold standard for characterizing microglial heterogeneity in vivo
- Spatial transcriptomics: Maps microglial states to specific brain regions and pathological features
- TSPO-PET imaging: Translocator protein PET tracers (11C-PK11195, 18F-DPA-714) detect activated microglia in living patients
- Flow cytometry/CyTOF: Multi-parameter analysis of surface markers and intracellular signaling
- Morphological analysis: Quantification of microglial branching, soma size, and process dynamics via two-photon microscopy
- [Crispr Gene Editing[/treatments/[crispr-gene-editing[/treatments/[crispr-gene-editing[/treatments/[crispr-gene-editing--TEMP--/treatments)--FIX--
- [Deep Brain Stimulation[/treatments/[deep-brain-stimulation[/treatments/[deep-brain-stimulation[/treatments/[deep-brain-stimulation--TEMP--/treatments)--FIX--
- [Transcranial Magnetic Stimulation[/treatments/[transcranial-magnetic-stimulation[/treatments/[transcranial-magnetic-stimulation[/treatments/[transcranial-magnetic-stimulation--TEMP--/treatments)--FIX--
- [Vagus Nerve Stimulation[/treatments/[vagus-nerve-stimulation[/treatments/[vagus-nerve-stimulation[/treatments/[vagus-nerve-stimulation--TEMP--/treatments)--FIX--
- [All Mechanisms[/[mechanisms[/[mechanisms[/[mechanisms[/mechanisms
- Orihuela R, et al. (2016). Microglial M1/M2 polarization and metabolic states. Frontiers in Cellular Neuroscience, 10, 136. . [DOI
- Cherry JD, et al. (2014). neuroinflammation and M2 microglia: the good, the bad, and the inflamed. Journal of neuroinflammation, 11, 98. . [DOI
- Ransohoff RM. (2016). A polarizing question: do M1 and M2 microglia exist? Nature Neuroscience, 19(8), 987-991. . [DOI
- Keren-Shaul H, et al. (2017). A unique microglia type associated with restricting development of Alzheimer's Disease. Cell, 169(7), 1276-1290. . [DOI
- Masuda T, et al. (2019). Spatial and temporal heterogeneity of mouse and human microglia at single-cell resolution. Nature, 566, 388-392. . [DOI
- Cheng J, et al. (2025). Decoding microglial polarization and metabolic reprogramming in neurodegenerative diseases. Aging and Disease. . [DOI
- Wang W-Y, et al. (2015). Role of pro-inflammatory cytokines released from microglia in Alzheimer's Disease. Annals of Translational Medicine, 3(10), 136. . [DOI
- Tang Y & Le W. (2016). Differential roles of M1 and M2 microglia in neurodegenerative diseases. Molecular Neurobiology, 53(2), 1181-1194. . [DOI
- Mandrekar-Colucci S, et al. (2012). Mechanisms underlying the rapid peroxisome proliferator-activated receptor-γ-mediated amyloid clearance and reversal of cognitive deficits in a murine model of Alzheimer's Disease. Journal of Neuroscience, 32(30), 10117-10128. . [DOI
- [PMC (2022). [microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX--
- [PMC (2018). Editorial: Microglial polarization in the pathogenesis and therapeutics of neurodegenerative diseases. PMC, PMC5976752. PMC)
- PLOS Biology (2025). Disease-associated microglia in neurodegenerative diseases: Friend or foe? PLOS Biology. . [DOI
🔴 Low Confidence
| Dimension |
Score |
| Supporting Studies |
12 references |
| Replication |
0% |
| Effect Sizes |
25% |
| Contradicting Evidence |
33% |
| Mechanistic Completeness |
50% |
Overall Confidence: 39%