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Interleukin 10 (IL-10), also known as human cytokine synthesis inhibitory factor (CSIF), is an anti- inflammatory
cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in au ...
. In humans, interleukin 10 is encoded by the ''IL10'' gene. IL-10 signals through a receptor complex consisting of two IL-10 receptor-1 and two IL-10 receptor-2 proteins. Consequently, the functional receptor consists of four IL-10 receptor molecules. IL-10 binding induces STAT3 signalling via the phosphorylation of the cytoplasmic tails of IL-10 receptor 1 + IL-10 receptor 2 by JAK1 and Tyk2 respectively.


Gene and protein structure

The IL-10 protein is a homodimer; each of its subunits is 178- amino-acid long. IL-10 is classified as a class-2 cytokine, a set of cytokines including IL-19, IL-20, IL-22, IL-24 (Mda-7), IL-26 and interferons type-I (IFN-alpha, -beta, -epsilon, -kappa, -omega), type-II (IFN-gamma) and type-III (IFN-lambda, also known as IL-28A, IL-28B, and IL-29).


Expression and synthesis

In humans, IL-10 is encoded by the ''IL10'' gene, which is located on chromosome 1 and comprises 5 exons, and is primarily produced by
monocyte Monocytes are a type of leukocyte or white blood cell. They are the largest type of leukocyte in blood and can differentiate into macrophages and conventional dendritic cells. As a part of the vertebrate innate immune system monocytes also ...
s and, to a lesser extent,
lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic a ...
s, namely type-II T helper cells (TH2), mast cells, CD4+CD25+Foxp3+ regulatory T cells, and in a certain subset of activated T cells and B cells. IL-10 can be produced by monocytes upon PD-1 triggering in these cells. IL-10 upregulation is also mediated by GPCRs, such as beta-2 adrenergic and type 2 cannabinoid receptors. The expression of IL-10 is minimal in unstimulated tissues and seems to require triggering by commensal or pathogenic flora. IL-10 expression is tightly regulated at the transcriptional and post-transcriptional level. Extensive IL-10 locus remodeling is observed in monocytes upon stimulation of TLR or Fc receptor pathways. IL-10 induction involves ERK1/2, p38 and NF-κB signalling and transcriptional activation via promoter binding of the transcription factors NF-κB and AP-1. IL-10 may autoregulate its expression via a negative feed-back loop involving autocrine stimulation of the IL-10 receptor and inhibition of the p38 signaling pathway. Additionally, IL-10 expression is extensively regulated at the post-transcriptional level, which may involve control of mRNA stability via AU-rich elements and by microRNAs such as let-7 or miR-106.


Function

IL-10 is a cytokine with multiple, pleiotropic, effects in immunoregulation and inflammation. It downregulates the expression of Th1 cytokines, MHC class II antigens, and co-stimulatory molecules on macrophages. It also enhances B cell survival, proliferation, and antibody production. IL-10 can block NF-κB activity, and is involved in the regulation of the JAK-STAT signaling pathway. Discovered in 1991, IL-10 was initially reported to suppress cytokine secretion, antigen presentation and CD4+ T cell activation. Further investigation has shown that IL-10 predominantly inhibits lipopolysaccharide (LPS) and bacterial product mediated induction of the pro-inflammatory cytokines TNFα, IL-1β, IL-12, and IFNγ secretion from Toll-Like Receptor (TLR) triggered myeloid lineage cells.


Effect on tumors

Over time a more nuanced picture of IL-10's function has emerged as treatment of tumor bearing mice has been shown to inhibit tumor metastasis. Additional investigation by multiple laboratories has generated data that further supports IL-10's immunostimulatory capacity in an immunoncology context. Expression of IL-10 from transfected tumor cell lines in IL-10 transgenic mice or dosing with IL-10 leads to control of primary tumor growth and decreased metastatic burden. More recently, PEGylated recombinant murine IL-10 (PEG-rMuIL-10) has been shown to induce IFNγ and CD8+ T cell dependent anti-tumor immunity. More specifically, PEGylated recombinant human IL-10 (PEG-rHuIL-10) has been shown to enhance CD8+ T cell secretion of the cytotoxic molecules Granzyme B and Perforin and potentiate T cell receptor dependent IFNγ secretion.


Role in disease

A study in mice has shown that IL-10 is also produced by mast cells, counteracting the inflammatory effect that these cells have at the site of an
allergic reaction Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derm ...
. IL-10 is capable of inhibiting synthesis of pro-inflammatory cytokines such as IFN-γ, IL-2, IL-3,
TNFα Tumor necrosis factor (TNF, cachexin, or cachectin; formerly known as tumor necrosis factor alpha or TNF-α) is an adipokine and a cytokine. TNF is a member of the TNF superfamily, which consists of various transmembrane proteins with a homolog ...
and GM-CSF made by cells such as macrophages and Th1 T cells. It also displays a potent ability to suppress the antigen-presentation capacity of antigen presenting cells; however, it is also stimulatory towards certain T cells (Th2) and mast cells and stimulates B cell maturation and antibody production. IL-10 checks the inducible form of Cyclo-oxygenase, Cyclo-oxygenase-2 (COX-2). Lack of IL-10 has been shown to cause COX activation and resultant Thromboxane receptor activation to cause vascular endothelial and cardiac dysfunctions in mice. Interleukin 10 knockout frail mice develop cardiac and vascular dysfunction with increased age. IL-10 is linked to the myokines, as exercise provokes an increase in circulating levels of IL-1ra, IL-10, and sTNF-R, suggesting that physical exercise fosters an environment of anti-inflammatory cytokines. Lower levels of IL-10 have been observed in individuals diagnosed with multiple sclerosis when compared to healthy individuals. Due to a decrease in IL-10 levels,
TNFα Tumor necrosis factor (TNF, cachexin, or cachectin; formerly known as tumor necrosis factor alpha or TNF-α) is an adipokine and a cytokine. TNF is a member of the TNF superfamily, which consists of various transmembrane proteins with a homolog ...
levels are not regulated effectively as IL-10 regulates the TNF-α-converting enzyme. As a result, TNFα levels rise and result in inflammation. TNFα itself induces demyelination of the oligodendroglial via TNF receptor 1, while chronic inflammation has been linked to demyelination of neurons. In melanoma cell lines, IL-10 modulates the surface expression of
NKG2D NKG2D is an activating receptor (transmembrane protein) belonging to the NKG2 family of C-type lectin-like receptors. NKG2D is encoded by ''KLRK1'' (killer cell lectin like receptor K1) gene which is located in the NK-gene complex (NKC) situated ...
ligands. In addition, Forkhead box protein 3 ( Foxp3) as a transcription factor is an essential molecular marker of regulatory T ( Treg) cells. Foxp3 polymorphism (rs3761548) might be involved in cancer progression like
gastric cancer Stomach cancer, also known as gastric cancer, is a cancer that develops from the lining of the stomach. Most cases of stomach cancers are gastric carcinomas, which can be divided into a number of subtypes, including gastric adenocarcinomas. Lym ...
through influencing Tregs function and the secretion of immunomodulatory cytokines such as IL-10,
IL-35 Interleukin 35 (IL-35) is a recently discovered anti-inflammatory cytokine from the IL-12 family. Member of IL-12 family - IL-35 is produced by wide range of regulatory lymphocytes and plays a role in immune suppression. IL-35 can block the develo ...
, and
TGF-β Transforming growth factor beta (TGF-β) is a multifunctional cytokine belonging to the transforming growth factor superfamily that includes three different mammalian isoforms (TGF-β 1 to 3, HGNC symbols TGFB1, TGFB2, TGFB3) and many other s ...
. A recent mouse study indicates that IL-10 regulates CD36, a key phagocytosis effector, promoting hematoma clearance after intracerebral hemorrhage. IL-10 deficiency aggravates traumatic brain injury in male but not female mice.


Clinical use or trials

Knockout studies in mice suggested the function of this cytokine as an essential immunoregulator in the intestinal tract. and, indeed, patients with Crohn's disease react favorably towards treatment with recombinant interleukin-10-producing bacteria, demonstrating the importance of IL-10 for counteracting the hyperactive immune response in the human body. Due to the data, thousands of patients with a variety of autoimmune diseases were treated with recombinant human IL-10 (rHuIL-10) in clinical trials. Contrary to expectations, rHuIL-10 treatment did not significantly impact disease in patients with Crohn's disease or rheumatoid arthritis. rHuIL-10 treatment initially exhibited promising clinical data in psoriasis, but failed to achieve clinical significance in a randomized, double blind, placebo controlled Phase II trial. Further investigation of rHuIL-10's effects in humans suggests that rather than inhibiting inflammation, rHuIL-10 is capable of exerting pro-inflammatory effects.


PEGylated forms

Further to these data, a Phase I immunoncology clinical trial is currently being conducted to assess the therapeutic capacity of
PEGylated PEGylation (or pegylation) is the process of both covalent and non-covalent attachment or amalgamation of polyethylene glycol (PEG, in pharmacy called macrogol) polymer chains to molecules and macrostructures, such as a drug, therapeutic protein ...
recombinant human IL-10 (PEG-rHuIL-10, AM0010). Consistent with preclinical immunoncology data, investigators report substantial anti-tumor efficacy. Contrary to the reported immunosuppressive effects of IL-10 generated ''in vitro'' and ''in vivo'', treatment of cancer patients with PEG-rHuIL-10 elicits a dose titratable induction of the immune stimulatory cytokines IFNγ, IL-18, IL-7, GM-CSF and IL-4. Furthermore, treated patients exhibit fold increases of peripheral CD8+ T cells expressing markers of activation, such as programmed death 1 (PD1)+, lymphocyte activation gene 3 (LAG3)+ and increased Fas Ligand (FasL) and a decrease in serum TGFβ. These findings are consistent with the published preclinical immunoncology reports using PEG-rMuIL-10 and with previous findings treating humans with rHuIL-10. These data suggest that while IL-10 can exert immunosuppressive effects in context of bacterial product stimulated myeloid cells, rHuIL-10/PEG-rHuIL-10 treatment of humans is predominantly immunostimulatory. AM0010 (aka pegilodecakin) is in phase 3 clinical trials.''Early Data Supports Phase 3 Trial of Pegilodecakin as Possible Treatment for Advanced Pancreatic Cancer''
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Interactions

IL-10 has been shown to
interact Advocates for Informed Choice, doing business as, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex trai ...
with Interleukin 10 receptor, alpha subunit. The receptor complex for IL-10 also requires the IL10R2 chain to initiate signalling. This ligand–receptor combination is found in birds and frogs, and is also likely to exist in bony fish.


References


Further reading

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External links

* * {{Interleukin receptor modulators Interleukins