Beyond Activation: Characterizing Microglial Functional Phenotypes

In the paper

“Even though IBA1 is often characterized as a typical microglial activation marker [8,9,10], it cannot be used to distinguish between functional microglial phenotypes [2].”

What the sources say

• Supported

  In “Microglia in human brains,” the paper says IBA-1 identifies all microglia and is not useful for identifying their immune phenotype or polarity. This directly supports the attributed claim. (LLM, conf=0.95)

  cites [2] Walker, 2015, Immune phenotypes of microglia in human neurodegenerative disease: Challenges to detecting mi-croglial polarization in human brains, Alzheimers Res. Ther. source

In the paper

“Following the transient occlusion of the middle cerebral artery (MCA) in rats, the IBA1 staining density and intensity were strongly increased in the ischemic core and the ischemic border zone, compared to the non-affected hemisphere [13].”

What the sources say

• Supported

  The Results section, “Vascular and glial alterations in relation to the ischemic lesion in untreated animals,” reports that Iba staining density and intensity were highest in the ischemic core, lower in the border zone, and lower still in the contralateral striatum, with significant differences between regions. This supports increased staining in both ischemic regions relative to the non-affected hemisphere. (LLM, conf=0.91)

  cites [13] Michalski, 2017, Delayed histochemical alterations within the neurovascular unit due to transient focal cerebral ischemia and experimental treatment with neurotrophic factors, PLoS ONE source

In the paper

“However, as we will describe in this review, associating single markers to a distinct phenotype is difficult, since most markers are expressed in several or even all microglial functional states (Figure 1, [2]).”

What the sources say

• Partly supported

  The Abstract says that widely used microglial markers do not distinguish different phenotypes, and the CD68 section says that both M1- and M2-polarized cells can express CD68. These passages support the difficulty of assigning a phenotype from a single marker, but do not establish that most markers are expressed in several or all functional states. Page numbers are unavailable in our copy. (LLM, conf=0.82)

  cites [2] Walker, 2015, Immune phenotypes of microglia in human neurodegenerative disease: Challenges to detecting mi-croglial polarization in human brains, Alzheimers Res. Ther. sourceExperimental — accuracy not yet measured

In the paper

“While the distribution of microglia varies between different brain regions [11], the expression of allograft inflammatory factor 1 (AIF-1, gene for IBA1) on microglia does not differ between white matter and grey matter [12].”

What the sources say

• Supported

  The Results section on primary human microglia states that AIF-1 expression did not differ between microglia derived from white matter and grey matter. This directly supports the attributed comparison; the measurements were made in cultured, tissue-derived microglia. (LLM, conf=0.93)

  cites [12] Vlaar, 2019, Regulation of microglial TMEM119 and P2RY12 immunoreactivity in multiple sclerosis white and grey matter lesions is dependent on their inflammatory envi-ronment, Acta Neuropathol. Commun. source

In the paper

“In contrast to so-called homeostatic microglial markers, such as transmembrane protein (TMEM-)119 or P2RY12, IBA1 is also expressed by peripheral macrophages [4,5,6,7].”

What the sources say

• Partly supported

  Results §3.4 reports that most recruited, donor-derived GFP+ cells in the brain expressed Iba1, supporting the point that IBA1 is not restricted to resident microglia. The paper does not address TMEM119 or P2RY12 or compare their expression with IBA1, so it does not support that part of the sentence. (LLM, conf=0.85)

  cites [4] Buckman, 2014, Obesity induced by a high-fat diet is associated with increased immune cell entry into the central nervous system, Brain Behav. Immun. sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites [5] 2007, Allograft inflammatory factor-1/Ionized calcium-binding adapter molecule 1 is specifically expressed by most subpopulations of macrophages and spermatids in testis, Cell Tissue Res. source
• ?Not checked — no full text of the sourcecites [6] Leone, 2006, Characterization of human monocyte-derived mi-croglia-like cells, Glia source
• ?Not checked — no full text of the sourcecites [7] Sasaki, 2001, Iba1 Is an Actin-Cross-Linking Protein in Macrophages/Microglia, Biochem. Biophys. Res. Commun. source

In the paper

“In contrast, studying the long-term effects of a high-fat, high-carbohydrate diet (HFCD) in the hippocampus of rats, Gzielo et al. [19] showed that the area fraction covered by IBA1-positive cells was reduced after consumption for one year.”

What the sources say

• Supported

  The Introduction states that the rats received a high-fat, high-carbohydrate diet for 12 months. The Results (Area Fraction) report significantly lower hippocampal Iba1-immunoreactive area fraction in those rats than in controls. (LLM, conf=0.94)

  cites [19] Gzielo, 2016, Long-Term Consumption of High-Fat Diet in Rats: Effects on Microglial and Astrocytic Morphology and Neuronal Nitric Oxide Synthase Expression, Cell. Mol. Neurobiol. source

In the paper

“In fact, we have shown that dystrophic, much more than activated microglia are present in human AD [83,104,107].”

What the sources say

• Supported

  The Discussion reports dystrophic microglia accompanying neuritic plaques and says the authors did not observe activated microglia across cases ranging from no to severe AD pathology. This supports the citing sentence’s comparison in human AD. (LLM, conf=0.92)

  cites [83] Streit, 2009, Dystrophic (senescent) rather than activated microglial cells are associated with tau pathology and likely precede neurodegeneration in Alzheimer’s disease, Acta Neuropathol. source
• ?Not checked — no full text of the sourcecites [104] Streit, 2018, Microglial activation occurs late during preclinical Alzheimer’s disease, Glia source
• ?Not checked — no full text of the sourcecites [107] Streit, 2020, Dystrophic microglia in late-onset Alzheimer’s disease, Glia source

In the paper

“CD74 was characterized as a cell surface receptor for the macrophage migration inhibitory factor (MIF, [70,71]).”

What the sources say

• Supported

  The section “CD74 Is A Receptor for MIF Cytokine” states that CD74 was identified as the MIF receptor and that MIF binds its extracellular domain. The “CD74” section also describes CD74 expression on cell surfaces. Page numbers are not provided in the supplied copy. (LLM, conf=0.94)

  cites [70] Farr, 2020, Role of MIF Cytokine/CD74 Receptor Pathway in Protecting Against Injury and Promoting Repair, Front. Immunol. source
• Supported

  The Abstract identifies CD74 as a high-affinity binding protein for MIF and reports that MIF binds its extracellular domain. The Discussion describes CD74 as a membrane receptor for MIF and confirms that CD74 is expressed on the cell surface. (LLM, conf=0.94)

  cites [71] Leng, 2003, MIF Signal Transduction Initiated by Binding to CD, J. Exp. Med. source

In the paper

“and microglia upregulate HLA-DR in response to IFNγ stimulation [27].”

What the sources say

• Supported

  The Introduction explicitly states that microglia upregulate HLA-DR in response to interferon (IFN)-γ stimulation. The claim accurately paraphrases that statement. (LLM, conf=0.95)

  cites [27] Hendrickx, 2017, Staining of HLA-DR, Iba1 and CD68 in human microglia reveals partially overlapping expression depending on cellular morphology and pathology, J. Neuroimmunol. source

In the paper

“while rodent studies even demonstrated an expression of 98% of CD45lowCD11b+ cells in adult animals [41].”

What the sources say

• Supported

  In “Custom Anti-Tmem119 Monoclonal Antibodies Specifically Identify Microglia,” the authors report that 98.1 ± 0.6% of CD45loCD11b+ cells were Tmem119+ in adult (P60) mice. This supports the citing sentence’s rounded 98% figure for adult rodents. (LLM, conf=0.94)

  cites [41] Bennett, 2016, New tools for studying microglia in the mouse and human CNS, Proc. Natl. Acad. Sci. USA source

In the paper

“TMEM119 and P2RY12 are especially useful, since they have been shown to be expressed solely by microglial cells and not by infiltrating macrophages [41,42,43].”

What the sources say

• Partly supported

  In “Macrophages After CNS Inflammation and Injury” (page not available), the paper reports that Tmem119 labels resident microglia but not infiltrating macrophages. It lists P2ry12 as a microglia-enriched candidate in “Tmem119 mRNA Expression Is Highly Enriched” (page not available), but does not establish that P2ry12 is expressed solely by microglia or absent from infiltrating macrophages. (LLM, conf=0.88)

  cites [41] Bennett, 2016, New tools for studying microglia in the mouse and human CNS, Proc. Natl. Acad. Sci. USA sourceExperimental — accuracy not yet measured
• Supported

  In Results (‘Identification of a unique microglial signature’; page unavailable), the paper identifies both Tmem119 and P2ry12 as microglial genes not detected in the other immune cells, monocytes, or organ-specific macrophages tested. Results (‘Identification of unique microglial surface molecules’; page unavailable) further show that recruited monocytes in EAE mice lacked P2ry12 while resident microglia expressed it. (LLM, conf=0.89)

  cites [42] Butovsky, 2014, Identification of a unique TGF-β–dependent molecular and functional signature in microglia, Nat. Neurosci. source
• Partly supported

  The Results (Microglia vs. Macrophages; page not provided) list Tmem119 and P2ry12 among transcripts unique to microglia in a comparison with peritoneal macrophages. The study did not test infiltrating macrophages, so it does not establish that these markers are absent from that population. (LLM, conf=0.86)

  cites [43] Hickman, 2013, The microglial sensome revealed by direct RNA sequencing, Nat. Neurosci. sourceExperimental — accuracy not yet measured

In the paper

“Recent experiments using deep sequencing revealed differences not only depending on the brain region, but also on age, gender, and pathology [28,39,99,102,108,109].”

What the sources say

• Partly supported

  The Results report single-cell RNA sequencing differences associated with Alzheimer’s pathology and a larger disease-associated microglia population in aged than young mice. The paper also locates these cells near plaques, but the passages do not establish microglial differences by brain region or gender; the Results describe wild-type controls as sex-matched rather than reporting a sex comparison. Page numbers are unavailable in our copy. (LLM, conf=0.88)

  cites [28] Spinrad, 2017, A Unique Microglia Type Associated with Restricting Development of Alzheimer’s Disease, Cell sourceExperimental — accuracy not yet measured
• Partly supported

  The Results (Nature and distribution of the single-cell RNA sequencing data; page unavailable) report differences in cluster frequencies between surgical and autopsy samples, but say more sampling is needed to determine whether brain region or age explains them. The Discussion (page unavailable) reports a microglial subset reduced in Alzheimer’s disease, supporting the pathology component. The cited passages do not establish differences by gender. (LLM, conf=0.90)

  cites [39] Olah, 2020, Single cell RNA sequencing of human microglia uncovers a subset associated with Alzheimer’s disease, Nat. Commun. sourceExperimental — accuracy not yet measured
• Partly supported

  The Discussion and Results report sequencing-based differences between cerebellar and striatal microglia. The Online Methods list mice of different ages and sexes, but do not establish separate age- or sex-dependent differences; the Discussion compares the regional signature with disease-associated microglia rather than reporting sequencing differences across pathologies. Pages are not provided in our copy. (LLM, conf=0.88)

  cites [99] Ayata, 2018, Epigenetic regulation of brain region-specific microglia clearance activity, Nat. Neurosci. sourceExperimental — accuracy not yet measured
• Partly supported

  The Results report a regionally restricted microglial state in developing axon tracts, and the Abstract reports changes with age and after demyelinating injury. But the Results section on sex finds almost no difference in microglial clustering between males and females; only one very small cluster was enriched in females. Thus, the paper does not support gender as a comparable source of microglial differences. Page numbers are not available in our copy. (LLM, conf=0.88)

  cites [102] Hammond, 2019, Single-Cell RNA Sequencing of Microglia throughout the Mouse Lifespan and in the Injured Brain Reveals Complex Cell-State Changes, Immunity sourceExperimental — accuracy not yet measured
• Partly supported

  The Abstract and Results (page numbers not supplied) report developmental-stage differences and a microglial subset concentrated in developing white matter. The Discussion reports little overt regional transcriptomic difference among classical adult microglia, so the regional claim needs that qualification. The paper compares its findings with disease-associated microglia, but does not report differences by gender or experiments comparing microglia across pathologies. (LLM, conf=0.88)

  cites [108] Li, 2019, Developmental Heterogeneity of Microglia and Brain Myeloid Cells Revealed by Deep Single-Cell RNA Sequencing, Neuron sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites [109] Patir, 2019, A core transcriptional signature of human microglia: Derivation and utility in describing region-dependent alterations associated with Alzheimer’s disease, Glia source

In the paper

“As a macrophage marker it is not solely expressed in microglia, but also in other macrophages, neutrophils, and monocytes [100].”

What the sources say

• Supported

  The Results section (“Identification of microglia-specific marker genes”) identifies CD68 as a widely used microglia marker and reports its expression in macrophages, neutrophils, and monocytes. This directly supports the claim that CD68 is not specific to microglia. (LLM, conf=0.95)

  cites [100] Chiu, 2013, A Neurodegeneration-Specific Gene-Expression Signature of Acutely Isolated Microglia from an Amyotrophic Lateral Sclerosis Mouse Model, Cell Rep. source

In the paper

“In Parkinson’s disease, an increased number of amoeboid, CD68-positive microglia were found compared to incidental Lewy body disease and control cases [103], suggesting active phagocytosis.”

What the sources say

• Supported

  The Results section reports significantly more CD68-positive amoeboid microglia in the substantia nigra of Parkinson’s disease patients than in both incidental Lewy body disease and control cases. It also reports the same comparison in the hippocampus, especially in CA2 and CA3. The supplied passages do not give page numbers. (LLM, conf=0.95)

  cites [103] Doorn, 2014, Microglial phenotypes and toll-like receptor 2 in the substantia nigra and hippocampus of incidental Lewy body disease cases and Parkinson’s disease patients, Acta Neuropathol. Commun. source

In the paper

“However, Van Olst et al. [97] demonstrated no increased expression of CD68 in multiple sclerosis, therefore emphasizing the importance of using several markers in order to describe the microglial phenotypes as thoroughly as possible.”

What the sources say

• Partly supported

  The Results section reports that CD68 expression in cortical microglia was not different overall between progressive MS donors and controls. But its subgroup analysis identifies high CD68 expression in the MS1 group, so the unqualified statement that there was no increased expression in MS omits an important exception. Page numbers are unavailable in our copy. (LLM, conf=0.88)

  cites [97] Picon, 2021, Meningeal inflammation in multiple sclerosis induces phenotypic changes in cortical microglia that differentially associate with neurodegeneration, Acta Neuropathol. sourceExperimental — accuracy not yet measured

In the paper

“In contrast, Kenkhuis et al. [47] demonstrated a microglial subset with an increased expression of the iron storage protein ferritin light chain (FTL) and IBA1, while exhibiting a decrease in TMEM119 and P2RY12 expression. This microglial subset presented a morphologically dystrophic phenotype.”

What the sources say

• Supported

  The Results section, “FTL+Iba1+-microglia have a dystrophic morphological appearance,” reports that C1 microglia were predominantly dystrophic and had pronounced FTL and increased Iba1 alongside decreased TMEM119 and P2RY12. The Conclusion likewise identifies dystrophic FTL+Iba1+TMEM119−P2RY12− microglia in Alzheimer’s disease patients. (LLM, conf=0.95)

  cites [47] Kenkhuis, 2021, Iron loading is a prominent feature of activated microglia in Alzheimer’s disease patients, Acta Neuropathol. Commun. source

In the paper

“However, human microglia in all morphological states show a distinct expression of CD74 (Figure 1, [76]), pointing to a potentially important species difference.”

What the sources say

• Partly supported

  The Results (Immunocytochemistry; page unavailable) show CD74 labeling in microglia from Alzheimer’s disease cases, supporting the expression part of the claim. They report no microglial labeling in controls, however, and the Discussion says increased CD74 was found only in resting or mildly active microglia. The paper therefore does not support expression across all morphological states of human microglia. (LLM, conf=0.88)

  cites [76] Bryan, 2008, Expression of CD74 is increased in neurofibrillary tangles in Alzheimer’s disease, Mol. Neurodegener. sourceExperimental — accuracy not yet measured

In the paper

“Microglia expressing MHCII can present processed antigens to CD4-positive (CD4+) T-lymphocytes [27], and microglia upregulate HLA-DR in response to IFNγ stimulation [27].”

What the sources say

• Supported

  The Introduction states that HLA-DR, a human MHC class II molecule, presents processed extracellular antigens to CD4+ helper T lymphocytes. The later discussion reiterates this function. This supports the attributed claim about MHCII-expressing microglia. (LLM, conf=0.94)

  cites [27] Hendrickx, 2017, Staining of HLA-DR, Iba1 and CD68 in human microglia reveals partially overlapping expression depending on cellular morphology and pathology, J. Neuroimmunol. source

In the paper

“Interestingly, an increase in these IBA1-free areas was associated with hepatic pathologies.”

In the paper

“We have shown that TREM2 is the highest upregulated mRNA in microdissected periplaque areas [32].”

What the sources say

• ?Not checked — no full text of the sourcecites [32] Frank, 2008, TREM2 is upregulated in amyloid plaque-associated microglia in aged APP23 transgenic mice, Glia source

In the paper

“Histopathologically, it is clear that even neighboring microglial cells can exhibit fundamental differences in their shape and protein expression profile (Figure 3L).”

In the paper

“Therefore, we proposed a novel microglial phenotype characterized by the absence of IBA1 (Figure 2).”

In the paper

“IBA1 reliably stains ramified, activated, amoeboid and dystrophic microglia (Figure 1).”

In the paper

“However, ascribing functions merely based on morphology and/or antigen expression may result in oversimplifications, such as M1/M2 (e.g., [1]).”

What the sources say

• ?Not checked — no full text of the sourcecites [1] Ransohoff, 2016, A polarizing question: Do M1 and M2 microglia exist?, Nat. Neurosci. source

In the paper

“they seem to have an “expiration date” limiting their capacity to phagocytose and support neurons.”

In the paper

“However, in human samples CD74 was not specific for morphologically activated microglia.”

In the paper

“In human brains, at least 50% of the IBA1-positive microglial population were positive for TMEM119 [45], while rodent studies even demonstrated an expression of 98% of CD45lowCD11b+ cells in adult animals [41].”

What the sources say

• ?Not checked — no full text of the sourcecites [45] Satoh, 2016, TMEM119 marks a subset of microglia in the human brain, Neuropathology source

In the paper

“Studies have not discriminated between a reduction in the total microglial numbers and a decreased expression of IBA1, since many use IBA1 as the sole microglial marker.”