Affinage

FOLR2

Folate receptor beta · UniProt P14207

Length
255 aa
Mass
29.3 kDa
Annotated
2026-06-09
25 papers in source corpus 11 papers cited in narrative 13 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 2/4 claims corpus-supported (50%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

FOLR2 encodes folate receptor beta (FRβ), a folate-binding protein that functions as a folate uptake receptor and serves as a defining marker of tissue-resident macrophages, in which it is expressed on mature myeloid cells but not on CD34+ hematopoietic stem cells (PMID:26898190). Its transcription in myeloid cells is driven by the PU.1 transcription factor acting through a cluster of PU.1-binding elements upstream of the first exon (PMID:32532019), and during M-CSF-driven macrophage differentiation in skin FRβ expression depends on intrinsic STAT6/ALK5 signaling, with co-expressed markers such as CD163 instead requiring fibroblast-derived laminin/collagen cues via an SHP1/STAT5 pathway (PMID:39720957). FOLR2+ macrophages occupy perivascular tumor stroma where they prime and activate CD8+ T cell cytotoxicity through antigen cross-presentation and the CXCL9-CXCR3 axis, supporting antitumor immunity (PMID:35325594, PMID:40045365, PMID:39702278). In other contexts these macrophages drive tissue remodeling, promoting myofibroblast differentiation in chronic kidney disease through WNT/β-catenin signaling (PMID:38272907). The folate-binding protein itself can be transferred between cells, with malignant cells acquiring functional FRβ by trogocytosis to enhance folate uptake.

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 2016 Medium

    Establishing where FRβ protein is and is not expressed defined its value as a lineage-restricted target, distinguishing mature myeloid cells from hematopoietic progenitors.

    Evidence Flow cytometry with a high-affinity FRβ antibody plus CAR T cytotoxicity and HSC colony assays in vitro and in xenografts

    PMID:26898190

    Open questions at the time
    • Does not address folate-binding function of FRβ
    • Expression pattern in non-myeloid tissues not defined
  2. 2018 Low

    A knockdown screen in a lung cancer line linked FOLR2 to PI3K/AKT/mTOR signaling and proliferation, raising a possible cell-intrinsic oncogenic role.

    Evidence siRNA knockdown with Western blot, viability, cell cycle and apoptosis readouts in NCI-H1650 cells

    PMID:30415267

    Open questions at the time
    • No rescue or reconstitution experiment
    • NSCLC cell line context may not reflect canonical FRβ macrophage biology
    • Mechanism connecting FRβ to AKT/mTOR unestablished
  3. 2020 Medium

    Identifying PU.1 as the transcriptional driver explained why FOLR2 is restricted to the myeloid lineage.

    Evidence siRNA knockdown of PU.1 plus luciferase reporter analysis of the FOLR2 proximal regulatory region

    PMID:32532019

    Open questions at the time
    • Other co-regulators of macrophage-specific expression not defined
    • Does not address signal-dependent tuning of expression
  4. 2022 Medium

    Localizing FOLR2+ macrophages to perivascular tumor stroma and showing they prime CD8+ T cells reframed FRβ+ macrophages as immunostimulatory players in the tumor microenvironment.

    Evidence Immunofluorescence localization and ex vivo CD8+ T cell priming coculture in breast cancer

    PMID:35325594

    Open questions at the time
    • Molecular mechanism of priming not resolved here
    • Causal contribution to tumor control in vivo not shown
  5. 2024 Medium

    Dissecting FRβ versus CD163 induction during macrophage differentiation separated cell-intrinsic from microenvironmental control of the FRβ+ macrophage phenotype.

    Evidence scRNA-seq, fibroblast coculture, and pharmacological inhibition of STAT6/ALK5/SHP1 in skin macrophages

    PMID:39720957

    Open questions at the time
    • Direct STAT6/ALK5 binding at the FOLR2 locus not shown
    • Generalizability beyond skin macrophages untested
  6. 2024 Medium

    Showing FOLR2+ macrophages drive fibroblast-to-myofibroblast conversion via WNT/β-catenin identified a pro-fibrotic, tissue-remodeling role distinct from their immune functions.

    Evidence Macrophage-fibroblast coculture, WNT/β-catenin pathway analysis, scRNA-seq and multiplex IHC in chronic kidney disease

    PMID:38272907

    Open questions at the time
    • WNT ligand source and identity not defined
    • In vivo genetic depletion not performed
  7. 2024 Medium

    Identifying FOLR2 as a direct miR-622 target connected its loss to cell cycle progression in colorectal cancer.

    Evidence Dual luciferase target validation with gain- and loss-of-function experiments in vitro and in vivo

    PMID:38166756

    Open questions at the time
    • Whether FRβ acts cell-intrinsically in tumor cells or via macrophages unclear
    • Mechanism of cell cycle suppression by FRβ not defined
  8. 2024 Medium

    Demonstrating antigen cross-presentation by FOLR2+ macrophages and their epithelial-driven necroptosis tied their abundance to gastric cancer progression.

    Evidence scRNA-seq, multiplex IHC, FOLR2+/FOLR2- macrophage-CD8+ T cell cocultures in gastric cancer

    PMID:39702278

    Open questions at the time
    • APP-TNFRSF21 necroptosis axis correlative
    • Antigen specificity of cross-presentation not characterized
  9. 2025 Medium

    Defining the CXCL9-CXCR3 axis provided the molecular mechanism by which FOLR2+ macrophages activate CD8+ T cell cytotoxicity and mediate antitumor effects.

    Evidence scRNA-seq, bulk RNA-seq, coculture, and in vivo mouse experiments in breast cancer

    PMID:40045365

    Open questions at the time
    • Upstream signals inducing CXCL9 secretion not resolved
    • Reconciliation with immunosuppressive contexts not addressed
  10. 2025 Low

    Showing FOLR2+ macrophages can also suppress CD8+ T cells via PD-L1 and IL-10 revealed context-dependent, opposing immune functions.

    Evidence Ex vivo fresh tumor tissue culture, multiplex IHC and transcriptional analysis in gastric cancer

    PMID:41263393

    Open questions at the time
    • No full mechanistic reconstitution of IL-10/PD-L1 suppression
    • Conflicts with stimulatory roles reported elsewhere remain unreconciled
  11. 2025 Low

    Trogocytic transfer of functional FRβ from nurse-like cells to CLL cells linked the receptor's folate-uptake function to cancer cell proliferation.

    Evidence Primary patient cell coculture, flow cytometry, and multiplex immunofluorescence of CLL lymph nodes (preprint)

    Open questions at the time
    • Trogocytosis mechanism inferred from correlative coculture data
    • Preprint, not independently confirmed
    • Direct demonstration of folate flux through transferred receptor incomplete
  12. 2026 Low

    Linking IDH2-driven mitochondrial dysfunction to a pro-inflammatory shift in testicular FOLR2+ macrophages connected metabolic state to their phenotypic plasticity in aging.

    Evidence scRNA-seq, multiplex immunofluorescence, and pharmacological IDH2 inhibition in aging mouse testes

    PMID:41618065

    Open questions at the time
    • IDH2 link is pharmacological without genetic reconstitution
    • CCL8-CCR2/CCR5 recruitment axis inferred from transcriptomics

Open questions

Synthesis pass · forward-looking unresolved questions
  • How FRβ's folate-binding biochemistry mechanistically governs the divergent immunostimulatory versus immunosuppressive and pro-fibrotic behaviors of FOLR2+ macrophages remains unresolved.
  • No structural model of FRβ ligand binding in the corpus
  • Context determinants of stimulatory vs suppressive macrophage states undefined
  • Whether folate uptake itself drives macrophage phenotype is unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0038024 cargo receptor activity 2
Localization
GO:0005886 plasma membrane 1
Pathway
R-HSA-168256 Immune System 3

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2020 FOLR2 gene expression in macrophages is transcriptionally regulated by the PU.1 transcription factor. PU.1-binding elements were identified upstream of the first exon of FOLR2, and siRNA-mediated knockdown of PU.1 reduced FOLR2 expression in myeloid cells. Functional analysis of the proximal regulatory region of FOLR2 confirmed dependence on a cluster of PU.1-binding sequences. siRNA knockdown, luciferase reporter assay of FOLR2 proximal regulatory region, bioinformatic identification of PU.1-binding elements Cells Medium 32532019
2022 FOLR2+ tissue-resident macrophages localize in perivascular areas of the tumor stroma in breast cancer, where they physically interact with CD8+ T cells and efficiently prime effector CD8+ T cells ex vivo. Immunofluorescence localization, ex vivo co-culture priming assay, flow cytometry Cell Medium 35325594
2016 FRβ (FOLR2 protein) is expressed on mature myeloid-lineage hematopoietic cells (including CD14+ monocytes) but is nearly undetectable on CD34+ hematopoietic stem cells, as determined using a high-affinity (2.48 nM KD) FRβ-specific antibody. CAR T cells targeting FRβ lysed mature CD14+ monocytes while leaving HSC colony formation unaffected. Flow cytometry with high-affinity FRβ-specific antibody, in vitro cytotoxicity assay, HSC colony formation assay, in vivo xenograft model Leukemia Medium 26898190
2024 FOLR2 expression on macrophages is regulated during M-CSF-driven differentiation in skin via intrinsic STAT6 and ALK5 activity, without requiring heterotypic cellular crosstalk. In contrast, CD163 co-expression on the same FRβ/CD163+ S1 macrophage subset requires fibroblast-derived signals (laminin-α2 and type-V collagen) through an SHP1/STAT5-dependent pathway. Single-cell transcriptomics, flow cytometry, coculture experiments with fibroblasts, in silico ligand expression analysis, pharmacological inhibition of STAT6/ALK5/SHP1 Cellular and molecular life sciences : CMLS Medium 39720957
2024 FOLR2+ macrophages promote fibrosis in chronic kidney disease through a WNT/β-catenin-dependent pathway: inflammatory fibroblasts (CXCL-iFibro) attract and accumulate FOLR2+ macrophages, which in turn drive the switch of CXCL-iFibro into ECM-secreting myofibroblasts via WNT/β-catenin signaling. In vitro macrophage-fibroblast coculture, WNT/β-catenin pathway analysis, single-cell transcriptomics, multiplex immunohistochemistry Nature communications Medium 38272907
2018 Silencing of FOLR2 in the NCI-H1650 non-small cell lung cancer cell line inhibited phosphorylation of AKT, mTOR, and S6K1, reduced cell viability, arrested cells in G1 phase, decreased cyclin D1, and increased Bax/Bcl-2 ratio and apoptosis. siRNA-mediated gene knockdown, Western blot, CCK-8 viability assay, flow cytometry (cell cycle and apoptosis) Medical science monitor Low 30415267
2025 FOLR2+ macrophages in breast cancer activate CD8+ T cell cytotoxicity through the CXCL9-CXCR3 axis. FOLR2+ macrophages secrete CXCL9 which engages CXCR3 on CD8+ T cells, and animal experiments confirmed this axis mediates the antitumor effect of FOLR2+ macrophages. Single-cell RNA sequencing, bulk RNA sequencing, in vitro coculture, in vivo mouse experiments Breast cancer research : BCR Medium 40045365
2024 FOLR2+ macrophages activate CD8+ T cell cytotoxicity via antigen cross-presentation in gastric cancer progression. Epithelial cells induce necroptosis of FOLR2+ macrophages via the APP-TNFRSF21 axis, reducing their proportion from complete intestinal metaplasia to early gastric cancer. Single-cell RNA sequencing, multiplex immunohistochemical staining, in vitro coculture of FOLR2+/FOLR2- macrophages with CD8+ T cells, flow cytometry Journal of experimental & clinical cancer research : CR Medium 39702278
2025 FOLR2+ macrophages in gastric cancer suppress CD8+ T cell function by expressing PD-L1 and secreting IL-10. Disruption of IL-10 sensitizes anti-PD-1 blockade and promotes antitumor immunity in FOLR2+ TAM-high tumors, demonstrated in fresh tumor tissue culture. In vitro culture of fresh tumor tissue, multiplex immunohistochemistry, transcriptional data analysis International journal of surgery (London, England) Low 41263393
2024 miR-622 directly targets FOLR2 mRNA to promote colorectal cancer cell proliferation. FOLR2 was validated as a functional target of miR-622 via dual luciferase assay; FOLR2 negatively correlates with cell cycle gene signatures, and its suppression by miR-622 drives cell cycle progression. Dual luciferase reporter assay, gain-of-function and loss-of-function experiments in vitro and in vivo, bioinformatics BMC cancer Medium 38166756
2025 CLL cells acquire functional FOLR2 protein from nurse-like cells (NLCs) via trogocytosis, enhancing their folate uptake. FOLR2+ CLL cells (those that acquired FOLR2 by trogocytosis) are the predominant actively cycling cancer cell population. This was confirmed by multiplex immunofluorescence in CLL patient lymph nodes. Primary patient cell coculture, flow cytometry, multiplex immunofluorescence of lymph node biopsies, proliferation assays bioRxivpreprint Low
2024 FOLR2-encoded folate receptor beta (FRβ) was predicted and experimentally validated to bind PFNA, PFOA, and PFOS (but not PFHxS, PFBS, or GenX) by in vitro protein binding analysis, correlating with their in vivo neurodevelopmental toxicity in zebrafish. Reverse molecular docking (computational), in vitro protein binding assay, in vivo zebrafish loss-of-function and rescue experiments bioRxivpreprint Low
2026 In aging mouse testes, FOLR2+ resident macrophages undergo a phenotypic transition toward a pro-inflammatory state driven by mitochondrial metabolic dysfunction, specifically inhibition of IDH2 (a TCA cycle enzyme). This transition facilitates recruitment of monocytes and CD8+ T cells via the CCL8-CCR2/CCR5 axis. Single-cell RNA sequencing, multiplex immunofluorescence, IDH2 inhibition experiments GeroScience Low 41618065

Source papers

Stage 0 corpus · 25 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2022 Tissue-resident FOLR2+ macrophages associate with CD8+ T cell infiltration in human breast cancer. Cell 456 35325594
2016 High-affinity FRβ-specific CAR T cells eradicate AML and normal myeloid lineage without HSC toxicity. Leukemia 108 26898190
2024 WNT-dependent interaction between inflammatory fibroblasts and FOLR2+ macrophages promotes fibrosis in chronic kidney disease. Nature communications 49 38272907
2020 Folate Receptor β (FRβ) Expression in Tissue-Resident and Tumor-Associated Macrophages Associates with and Depends on the Expression of PU.1. Cells 41 32532019
2022 A Population of TIM4+FOLR2+ Macrophages Localized in Tertiary Lymphoid Structures Correlates to an Active Immune Infiltrate Across Several Cancer Types. Cancer immunology research 40 36122412
2010 Association of folate receptor (FOLR1, FOLR2, FOLR3) and reduced folate carrier (SLC19A1) genes with meningomyelocele. Birth defects research. Part A, Clinical and molecular teratology 34 20683905
2023 Single-cell profiling reveals the trajectory of FOLR2-expressing tumor-associated macrophages to regulatory T cells in the progression of lung adenocarcinoma. Cell death & disease 32 37532692
2011 Macrophage folate receptor-β (FR-β) expression in auto-immune inflammatory rheumatic diseases: a forthcoming marker for cardiovascular risk? Autoimmunity reviews 32 22094710
2024 FOLR2+ macrophage depletion from intestinal metaplasia to early gastric cancer: single-cell sequencing insight into gastric cancer progression. Journal of experimental & clinical cancer research : CR 10 39702278
2018 Silencing the FOLR2 Gene Inhibits Cell Proliferation and Increases Apoptosis in the NCI-H1650 Non-Small Cell Lung Cancer Cell Line via Inhibition of AKT/Mammalian Target of Rapamycin (mTOR)/Ribosomal Protein S6 Kinase 1 (S6K1) Signaling. Medical science monitor : international medical journal of experimental and clinical research 10 30415267
2025 Unveiling the key mechanisms of FOLR2+ macrophage-mediated antitumor immunity in breast cancer using integrated single-cell RNA sequencing and bulk RNA sequencing. Breast cancer research : BCR 8 40045365
2024 Folate Receptor β (FRβ) Expression on Myeloid Cells and the Impact of Reticuloendothelial System on Folate-Functionalized Nanoparticles' Biodistribution in Cancer. Molecular pharmaceutics 8 39105761
2025 FOLR2+ macrophages in cancer: allies or enemies. Cell communication and signaling : CCS 7 40457348
2024 Guided monocyte fate to FRβ/CD163+ S1 macrophage antagonises atopic dermatitis via fibroblastic matrices in mouse hypodermis. Cellular and molecular life sciences : CMLS 6 39720957
2025 Single-cell to pre-clinical evaluation of Trem2, Folr2, and Slc7a7 as macrophage-associated biomarkers for atherosclerosis. Cardiovascular research 5 41206594
2024 microRNA-622 upregulates cell cycle process by targeting FOLR2 to promote CRC proliferation. BMC cancer 5 38166756
2024 Expression of the Folate Receptor Proteins FOLR1 and FOLR2 in Correlation With Clinicopathological Variables of Gastric Cancer. Cureus 3 38915965
2022 Association of polymorphisms of FOLR1 gene and FOLR2 gene and maternal folic acid supplementation with risk of ventricular septal defect: a case-control study. European journal of clinical nutrition 3 35273364
2025 Disrupting of tissue-resident FOLR2+tumour-associated macrophages-derived interleukin-10 improves anti-PD-1 efficacy in gastric cancer. International journal of surgery (London, England) 2 41263393
2026 Single-cell immune atlas of mouse testes unveils metabolic reprogramming of FOLR2 + macrophages in orchestrating testicular immunity during aging. GeroScience 1 41618065
2023 Mutational analysis of FOLR1 and FOLR2 genes in children with Myelomeningocele. Acta biochimica Polonica 1 37883728
2026 2-Deoxyglucose dendrimer-enabled niclosamide delivery to FRβ-expressing macrophages alleviates endometriosis progression and associated hyperalgesia. bioRxiv : the preprint server for biology 0 41727129
2025 Design and Synthesis of FR-β Targeting Chimeric Molecules for Reprogramming Tumor-Associated Macrophages Using 6-Substituted Pyrrolo[2,3-d]pyrimidines as Targeting Ligands. Journal of medicinal chemistry 0 40219974
2025 CD4+ skin resident memory T cells preferentially colocalize with dermal Folr2hi macrophages in contact hypersensitivity. Frontiers in immunology 0 40791604
2022 Association of periconceptional folate supplements and FOLR1 and FOLR2 gene polymorphisms with risk of congenital heart disease in offspring: A hospital-based case-control study. Zhong nan da xue xue bao. Yi xue ban = Journal of Central South University. Medical sciences 0 35545363

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