Cited by 1,455Cytokine Signaling Pathways and InteractionsNF-κB Signaling PathwaysRheumatoid Arthritis Research and Therapies

The DOI matches its Crossref record; 382 of the 390 references it cites were found in a registry or an index; 220 of the 329 sources its claims cite were checked for support.

IL-6 in inflammation, autoimmunity and cancer

Open access
Hirano, Toshio·2021·International Immunology

Abstract

IL-6 is involved both in immune responses and in inflammation, hematopoiesis, bone metabolism and embryonic development. IL-6 plays roles in chronic inflammation (closely related to chronic inflammatory diseases, autoimmune diseases and cancer) and even in the cytokine storm of corona virus disease 2019 (COVID-19). Acute inflammation during the immune response and wound healing is a well-controlled response, whereas chronic inflammation and the cytokine storm are uncontrolled inflammatory responses. Non-immune and immune cells, cytokines such as IL-1β, IL-6 and tumor necrosis factor alpha (TNFα) and transcription factors nuclear factor-kappa B (NF-κB) and signal transducer and activator of transcription 3 (STAT3) play central roles in inflammation. Synergistic interactions between NF-κB and STAT3 induce the hyper-activation of NF-κB followed by the production of various inflammatory cytokines. Because IL-6 is an NF-κB target, simultaneous activation of NF-κB and STAT3 in non-immune cells triggers a positive feedback loop of NF-κB activation by the IL-6–STAT3 axis. This positive feedback loop is called the IL-6 amplifier (IL-6 Amp) and is a key player in the local initiation model, which states that local initiators, such as senescence, obesity, stressors, infection, injury and smoking, trigger diseases by promoting interactions between non-immune cells and immune cells. This model counters dogma that holds that autoimmunity and oncogenesis are triggered by the breakdown of tissue-specific immune tolerance and oncogenic mutations, respectively. The IL-6 Amp is activated by a variety of local initiators, demonstrating that the IL-6–STAT3 axis is a critical target for treating diseases.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

IL-6 is a pleiotropic cytokine discovered in 1986 that acts through IL-6–STAT3 signaling and the IL-6 amplifier (IL-6 Amp), a STAT3/NF-κB-driven amplification loop, to link inflammation, autoimmunity and cancer. The review proposes a local initiation model in which infection, injury, stress, senescence, obesity and oncogenic mutations activate the IL-6 Amp in non-immune cells, recruiting immune cells and driving chronic disease.

Key findings

  • IL-6 is a prototypical member of the 10-member IL-6 family and signals via classic, trans-signaling and trans-presentation modes; trans-signaling expands IL-6 targets to cells expressing only gp130, including fibroblasts and endothelial cells.
  • IL-6–STAT3 signaling regulates Th17/Treg balance, plasma cell differentiation, dendritic cell maturation, M2 macrophages, MDSCs and PD-L1 expression, and promotes cancer cell survival, proliferation, EMT, angiogenesis and metastasis.
  • The IL-6 Amp synergistically amplifies IL-6 and other pro-inflammatory mediators through STAT3 and NF-κB; a comparative analysis found 202 of 1700 screened genes showed over 490 indications of association with autoimmune, metabolic, neurodegenerative and other chronic inflammatory diseases.
  • IL-6 correlates with prognosis across 23 cancer types; in mouse models, F759 mice spontaneously develop IL-6-dependent, CD4+ T-cell-dependent arthritis, while gp130Y757F/Y757F mice show gastric hyperproliferative lesions as early as 6 weeks.

Methods

  • Narrative review synthesizing mechanistic, genetic, mouse-model and clinical literature on IL-6 in inflammation, autoimmunity and cancer.
  • Discusses mouse models including F759, gp130Y757F/Y757F, IL-6 transgenic and IL-6-deficient mice, plus GWAS/SNP associations and clinical trials of anti-IL-6/IL-6R therapies.
  • No systematic search strategy, meta-analysis or primary data collection is described.

Limitations

  • Stated: many questions remain, including how sIL-6Rα is generated, the mechanism of STAT3–NF-κB synergy, and the genetic/environmental factors that destabilize the IL-6 Amp; current knowledge is insufficient to predict disease end stage or detailed process.
  • Stated: more study is needed on interactions among pro-inflammatory molecules and on real-time dynamics of receptor complexes and signaling molecules.
  • Evident from the text: as a narrative review, it does not systematically assess study quality or bias, and many mechanistic conclusions derive from mouse models and in vitro systems rather than human validation.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1093/intimm/dxaa078

Cites

382 of 382 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Figures

Fig. 1. IL-6 receptor and signaling. (A) IL-6 binding induces a hexameric complex composed of two molecules of IL-6, IL-6Rα and gp130 each, leading to the activation of JAKs associated with gp130 at Box1 and Box2. The phosphorylation of tyrosine 759 of gp130 is required for the gp130-mediated ERK–MAPK pathway via SHP2 and GAB adaptor molecules and essential for the SOCS3-mediated negative feedback loop. The distal four tyrosine residues of gp130 (Y767, Y814, Y905 and Y915) form a YXXQ motif, which is required for STAT3 activation. The YAP–Notch pathway is triggered by Yes. TRAF is associated with gp130 and inhibits the STAT3 signaling pathway. MiR-135a and miR-337-3p down-regulate JAK2 and STAT3, respectively. PIAS directly inhibits STAT3. All amino acid positions are of human gp130. (B) Three modes of gp130-mediated signaling. IL-6 acts on cells expressing both IL-6Rα and gp130 (classical signaling). The complex of IL-6 and sIL-6Rα acts like a novel cytokine on cells expressing only gp130 (trans-signaling). In the trans-presentation mode, IL-6 bound to IL-6Rα expressed on one type of cell acts on another cell type expressing gp130.
Fig. 1. IL-6 receptor and signaling. (A) IL-6 binding induces a hexameric complex composed of two molecules of IL-6, IL-6Rα and gp130 each, leading to the activation of JAKs associated with gp130 at Box1 and Box2. The phosphorylation of tyrosine 759 of gp130 is required for the gp130-mediated ERK–MAPK pathway via SHP2 and GAB adaptor molecules and essential for the SOCS3-mediated negative feedback loop. The distal four tyrosine residues of gp130 (Y767, Y814, Y905 and Y915) form a YXXQ motif, which is required for STAT3 activation. The YAP–Notch pathway is triggered by Yes. TRAF is associated with gp130 and inhibits the STAT3 signaling pathway. MiR-135a and miR-337-3p down-regulate JAK2 and STAT3, respectively. PIAS directly inhibits STAT3. All amino acid positions are of human gp130. (B) Three modes of gp130-mediated signaling. IL-6 acts on cells expressing both IL-6Rα and gp130 (classical signaling). The complex of IL-6 and sIL-6Rα acts like a novel cytokine on cells expressing only gp130 (trans-signaling). In the trans-presentation mode, IL-6 bound to IL-6Rα expressed on one type of cell acts on another cell type expressing gp130.CC BY-NC · PubMed Central
Fig. 2. IL-6/STAT3 in immunity. IL-6 promotes antibody production by either directly acting on plasma cells or indirectly promoting Tfh cell differentiation. IL-6/STAT3 together with TGFβ or IL-1β and IL-23 induces Th17 cells, while IL-6 inhibits the TGFβ/IL-2-induced generation of Treg cells. IL-2/STAT5 or IL-27/STAT1 inhibits the IL-6/STAT3-induced differentiation of Th17 cells. IL-6/STAT3 induces the conversion of Treg cells to Th17 cells, and this process is inhibited by IL-2. The IL-6/TGFβ and IL-2/TGFβ axes regulate the balance of Th17 and Treg cells; the former is pro-inflammatory and the latter anti-inflammatory. IL-6/STAT3 induces the differentiation of M2 macrophages and activates MDSCs, both of which have anti-tumor immunity effects. In addition, IL-6/STAT3 inhibits DC maturation and function. Finally, IL-6/STAT3 induces PD-L1 expression.
Fig. 2. IL-6/STAT3 in immunity. IL-6 promotes antibody production by either directly acting on plasma cells or indirectly promoting Tfh cell differentiation. IL-6/STAT3 together with TGFβ or IL-1β and IL-23 induces Th17 cells, while IL-6 inhibits the TGFβ/IL-2-induced generation of Treg cells. IL-2/STAT5 or IL-27/STAT1 inhibits the IL-6/STAT3-induced differentiation of Th17 cells. IL-6/STAT3 induces the conversion of Treg cells to Th17 cells, and this process is inhibited by IL-2. The IL-6/TGFβ and IL-2/TGFβ axes regulate the balance of Th17 and Treg cells; the former is pro-inflammatory and the latter anti-inflammatory. IL-6/STAT3 induces the differentiation of M2 macrophages and activates MDSCs, both of which have anti-tumor immunity effects. In addition, IL-6/STAT3 inhibits DC maturation and function. Finally, IL-6/STAT3 induces PD-L1 expression.CC BY-NC · PubMed Central
Fig. 3. The IL-6 Amp. STAT3 activators (e.g. IL-6) and NF-κB activators (e.g. IL-17 or TNFα) synergistically enhance the production of various pro-inflammatory mediators including IL-6 from non-immune cells in a manner dependent on STAT3 and NF-κB. This amplification mechanism is called the IL-6 amplifier (IL-6 Amp). The IL-6 Amp recruits immune cells such as activated T cells into the lesion by chemokines. The interaction between immune cells and non-immune cells further strengthens the IL-6 Amp. The IL-6 Amp enhances the expression of many genes involved in cell proliferation, survival, movement, inflammation, angiogenesis and so on.
Fig. 3. The IL-6 Amp. STAT3 activators (e.g. IL-6) and NF-κB activators (e.g. IL-17 or TNFα) synergistically enhance the production of various pro-inflammatory mediators including IL-6 from non-immune cells in a manner dependent on STAT3 and NF-κB. This amplification mechanism is called the IL-6 amplifier (IL-6 Amp). The IL-6 Amp recruits immune cells such as activated T cells into the lesion by chemokines. The interaction between immune cells and non-immune cells further strengthens the IL-6 Amp. The IL-6 Amp enhances the expression of many genes involved in cell proliferation, survival, movement, inflammation, angiogenesis and so on.CC BY-NC · PubMed Central
Fig. 4. Local initiation model. A variety of local initiators, such as infection, injury, stressors acting through neural networks, senescence, obesity, smoking and oncogenic mutations, activate both STAT3 and NF-κB, leading to activation of the IL-6 Amp in non-immune cells such as fibroblasts, epithelial cells, endothelial cells and adipocytes. The IL-6 Amp amplifies the production of IL-6 and other pro-inflammatory cytokines and growth factors. Chemokines produced by the IL-6 Amp recruit immune cells such as activated T cells to the lesion to interact with non-immune cells, leading to further activation of the IL-6 Amp. The IL-6 Amp becomes dysregulated depending on the genetic background and or other factors including the properties of local initiators, leading to chronic inflammatory diseases, autoimmune diseases and cancer.
Fig. 4. Local initiation model. A variety of local initiators, such as infection, injury, stressors acting through neural networks, senescence, obesity, smoking and oncogenic mutations, activate both STAT3 and NF-κB, leading to activation of the IL-6 Amp in non-immune cells such as fibroblasts, epithelial cells, endothelial cells and adipocytes. The IL-6 Amp amplifies the production of IL-6 and other pro-inflammatory cytokines and growth factors. Chemokines produced by the IL-6 Amp recruit immune cells such as activated T cells to the lesion to interact with non-immune cells, leading to further activation of the IL-6 Amp. The IL-6 Amp becomes dysregulated depending on the genetic background and or other factors including the properties of local initiators, leading to chronic inflammatory diseases, autoimmune diseases and cancer.CC BY-NC · PubMed Central
Fig. 5. A possible mechanism of SARS-CoV-1/2-induced cytokine storm. Because SARS-CoV-1/2 utilizes ACE2 as a receptor, virus infection decreases the cell surface expression of ACE2, which is a peptidase of angiotensin II (AngII), resulting in an increase of AngII. In addition, virus-induced lung injury activates ACE1, further increasing serum AngII levels. As a result, AT1R-mediated signaling is enhanced. In turn, so too is the inflammatory response, including TNFα and sIL-6Rα via ADAM17 activation. Virus infection itself activates signaling through pattern-recognition receptors (PRRs). Furthermore, virus-induced massive cell death can activate DAMP receptor-mediated signaling pathways. Moreover, virus infection activates and/or recruits lymphoid cells and myeloid cells in the lesion. All these events synergistically activate the IL-6 Amp through the interaction of STAT3 and NF-κB, leading to cytokine storm.
Fig. 5. A possible mechanism of SARS-CoV-1/2-induced cytokine storm. Because SARS-CoV-1/2 utilizes ACE2 as a receptor, virus infection decreases the cell surface expression of ACE2, which is a peptidase of angiotensin II (AngII), resulting in an increase of AngII. In addition, virus-induced lung injury activates ACE1, further increasing serum AngII levels. As a result, AT1R-mediated signaling is enhanced. In turn, so too is the inflammatory response, including TNFα and sIL-6Rα via ADAM17 activation. Virus infection itself activates signaling through pattern-recognition receptors (PRRs). Furthermore, virus-induced massive cell death can activate DAMP receptor-mediated signaling pathways. Moreover, virus infection activates and/or recruits lymphoid cells and myeloid cells in the lesion. All these events synergistically activate the IL-6 Amp through the interaction of STAT3 and NF-κB, leading to cytokine storm.CC BY-NC · PubMed Central

Verification

Claims the paper makes

71 Partly supported · 43 Supported · 41 Own interpretation · 31 No full text of the sources · 10 Supported so far · 7 No basis given · 6 Couldn’t confirm · 3 Not checked yet · accuracy not yet measured

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  • It may state two separate claims as one. 78
  • Probably not a substantial claim. 7
82 of 82
  • The authors state this as an assumption.

    The same cause can induce both RA and IL-6 expression.

    “Assuming that the same cause can induce both RA and IL-6 expression, such an intimate relationship could be explained.”
1 of 1

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Metadata

Authors
Hirano, T.
Affiliations
Hokkaido University (JP)
Corresponding author
Hirano, Toshio
Venue
International Immunology
Published
2020-12-18
Volume
33
Issue
3
Pages
127-148
ISSN
  • 0953-8178 (ISSN-L)
  • 1460-2377
OpenAlex
W3112344668
Cited by
1,453
References
390
Citations by year
2026: 246 · 2025: 394 · 2024: 326 · 2023: 273 · 2022: 165 · 2021: 49
FWCI
39.33
Type
journal article
Language
en
Open access
Locations
  • International Immunology (publishedVersion, cc-by-nc)
  • PubMed (publishedVersion)
  • Europe PMC (PubMed Central) (submittedVersion, cc-by-nc)
  • PubMed Central (submittedVersion, cc-by-nc)
  • QST-Repository (National Institutes for Quantum and Radiological Science and Technology) (submittedVersion, cc-by-nc-nd)
Topics
  • Life Sciences › Immunology and Microbiology › Immunology › Cytokine Signaling Pathways and Interactions
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cancer Research › NF-κB Signaling Pathways
  • Health Sciences › Medicine › Rheumatology › Rheumatoid Arthritis Research and Therapies
Keywords
interleukin-6, chronic inflammation, autoimmunity, cancer, NF-κB, STAT3, cytokine storm, COVID-19 pandemic, senescence, obesity, positive feedback loop, hematopoiesis, bone metabolism
MeSH terms
COVID-19, COVID-19 Drug Treatment, Animals, Humans, Inflammation, Neoplasms, Autoimmunity, Interleukin-6, STAT3 Transcription Factor

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