Interleukins: Definition, Function, History, and Common Families of Interleukins

They are a group of cytokines (secreted proteins and signal molecules) that are expressed in white blood cells [ leukocytes] ).

Interleukins can be divided into four main groups based on distinctive structural features. However, their amino acid sequence similarity is relatively weak (typically 15-25% identity). The human genome encodes more than 50 interleukins and related proteins.

The function of the immune system depends mainly on interleukins, and rare deficiencies of several of them have been described, all of them with autoimmune diseases or immunodeficiency.

Most interleukins are synthesized by CD4 helper T lymphocytes and through monocytes, macrophages, and endothelial cells. They promote the development and differentiation of T and B lymphocytes and hematopoietic cells.

Interleukin receptors on astrocytes in the hippocampus are also involved in the development of spatial memories in mice.

History and name

The name “interleukin” was chosen in 1979 to replace the different terms used by other research groups to designate interleukin 1 (lymphocyte activating factor, mitogenic protein, T cell replacement factor III, B cell-activating factor, differentiation of factor B cells, and “Heidikine”) and interleukin 2 (TSF, etc.).

This decision was made during the Second International Lymphokine Workshop in Switzerland (May 27-31, 1979, in Ermatingen, ‘near’ Interlaken).


The term interleukin is derived from (inter-) “as a means of communication,” and (-leucine), “which is derived from the fact that many of these proteins are produced by leukocytes and act on leukocytes.” The name is something of a relic.

Since then, it has been discovered that interleukins are produced by various cells in the body. The term was coined by Dr. Vern Paetkau from the University of Victoria.

Some interleukins are classified as lymphokines, cytokines produced by lymphocytes that mediate the immune response.

Common families of interleukins

Interleukin 1

Interleukin 1 alpha and interleukin one beta (Interleukin1 alpha and Interleukin1 beta) are cytokines that participate in the regulation of immune responses, inflammatory reactions, and hematopoiesis.

Two types of the interleukin-1 receptor, each with three similar extracellular immunoglobulins (Ig) domains, limited sequence similarity (28%), and different pharmacological characteristics, have been cloned from mouse and human cell lines: these have been termed type I and type II receptors.

The receptors exist in both transmembrane (TM) and soluble forms: the soluble receptor for Interleukin-1 is believed to be derived post-translationally from cleavage of the extracellular portion of membrane receptors.

Both interleukin-1 receptors (CD121a / Interleukin1R1, CD121b / Interleukin1R2) appear to be well conserved in evolution and are assigned to the exact chromosomal location.

Receptors can bind all three forms of Interleukin-1 (Interleukin-1 alpha, Interleukin-1 beta, and Interleukin-1 receptor antagonist).

The crystal structures of Interleukin1A and Interleukin1B have been resolved, showing them that they share the same 12-sheet beta-sheet structure as heparin-binding growth factors and Kunitz-type soybean trypsin inhibitors.

Beta sheets are arranged in 4 similar lobes around a central axis, eight threads that form an antiparallel beta-barrel. Several regions, especially the loop between strands 4 and 5, have been implicated in receptor binding.

Molecular cloning of the Interleukin 1 converting enzyme is generated by proteolytic cleavage of an inactive parent molecule. A protease encoding complementary DNA that carries out this cleavage has been cloned.

Recombinant expression allows cells to process Interleukin 1 Beta precursors to the mature form of the enzyme. Interleukin 1 also plays a role in the Central Nervous System.

Research indicates that mice with a genetic deletion of the Interleukin 1 type I receptor exhibit impaired hippocampal-dependent memory functioning and long-term potentiation. However, memories that do not depend on the integrity of the hippocampus appear to be avoided.

However, when mice with this gene deletion have wild-type neuronal precursor cells injected into their hippocampus, and these cells mature into astrocytes containing interleukin-1 receptors, the mice exhibit normal hippocampal-dependent memory function and partial restoration—long Long-term potentiation.

Interleukin 2

T lymphocytes regulate the growth and differentiation of T cells and specific B cells by releasing secreted protein factors.

These factors, interleukin 2 (IL2), are secreted by lectin- or antigen-stimulated T cells and have various physiological effects. Interleukin is a lymphokine that induces the proliferation of sensory T cells.

In addition, it acts on some B cells, through the specific binding of the receptor, as a growth factor and as a stimulant for the production of antibodies.

The protein is secreted as a single, glycosylated polypeptide, and cleavage of a signal sequence is required for its activity. The nuclear magnetic resonance solution suggests that the structure of Interleukin2 comprises a set of 4 helices (called AD), flanked by two shorter helices and several poorly defined loops.

Residues in the A helix and the loop region between the A and B helices are essential for receptor binding. Secondary structure analysis has suggested a similarity to Interleukin 4 and granulocyte-macrophage colony-stimulating factor (GMCSF).

Interleukin 3

Interleukin 3 (IL3) is a cytokine that regulates hematopoiesis by controlling granulocytes’ and macrophages’ production, differentiation, and function. The protein, which exists in vivo as a monomer, is produced in activated T cells and mast cells and is activated by cleavage of an N-terminal signal sequence.

Interleukin 3 is produced by T lymphocytes and T cell lymphomas only after stimulation with antigens, mitogens, or chemical activators such as phorbol esters.

However, interleukin3 is expressed in the WEHI-3B myelomonocytic leukemia cell line. The genetic shift of the cell line to constitutive production of Interleukin3 is believed to be the critical event in the development of this leukemia.

Interleukin 4

Interleukin 4 (IL4) is produced by CD4 + T cells specialized in assisting B cells in proliferating and undergoing class change recombination and somatic hypermutation.

Th2 cells, through the production of Interleukin-4, play an essential role in B cell responses involving class switch recombination with IgG1 and IgE isotypes.

Interleukin 5

Interleukin 5 (IL5), also known as eosinophil differentiation factor (EDF), is a lineage-specific cytokine for eosinophyllipoiesis.

It regulates the growth and activation of eosinophils and thus plays a vital role in diseases associated with increased eosinophil levels, including asthma.

Interleukin 5 has an overall fold similar to other cytokines (e.g., IL2, IL4, and granulocyte colony-stimulating factor), but while they exist as monomeric structures, interleukin 5 is a homodimer.

The fold contains a 4-alpha-helix antiparallel bundle with a left turn, connected by a 2-chain antiparallel beta-sheet. The monomers are held together by two interchain disulfide bonds.

Interleukin 6

Interleukin 6 (IL6), also known as B-cell stimulating factor 2 (BSF-2) and interferon beta-2, is a cytokine involved in various biological functions.

It plays an essential role in the eventual differentiation of B cells into immunoglobulin-secreting cells, as well as in the induction of myeloma/plasmacytoma growth, nerve cell differentiation, and, in hepatocytes, acute phase reactants.

Several other cytokines can be grouped with Interleukin 6 based on sequence similarity. These include granulocyte colony-stimulating factor (GCSF) and myelomonocytic growth factor (MGF).

Granulocyte colony-stimulating factor acts in hematopoiesis by affecting the production, differentiation, and function of 2 groups of related white blood cells.

Myelomonocytic growth factor also acts in hematopoiesis, stimulating the proliferation and formation of colonies of normal and transformed avian cells of the myeloid lineage.

Cytokines of the interleukin/granulocyte colony-stimulating factor / myelomonocytic growth factor family are glycoproteins of approximately 170 to 180 amino acid residues that contain four conserved cysteine ​​residues involved in two disulfide bonds.

They have a compact globular fold (similar to other interleukins), stabilized by the two disulfide bonds.

Half of the structure is dominated by a bundle of 4 alpha-helices with a left turn; the helices are antiparallel, with two connections above, which fall into a double-stranded antiparallel beta-sheet. The fourth alpha helix is ​​essential for the biological activity of the molecule.

Interleukins 7

Interleukin-7 is a hematopoietic growth factor secreted by stromal cells in the bone marrow and thymus. It is also produced by keratinocytes, dendritic cells, hepatocytes, neurons, and epithelial cells, but normal lymphocytes do not produce it.

Interleukin 8

Interleukin 8 (IL8 or chemokine (CXC motif) ligand 8, CXCL8) is a chemokine produced by macrophages and other cell types such as epithelial cells, airway smooth muscle cells, and endothelial cells.

Endothelial cells store interleukin-8 in their storage vesicles, the Weibel-Palade bodies.

In humans, the interleukin-8 protein is encoded by the CXCL8 gene. Interleukin-8 is initially produced as a 99 amino acid precursor peptide that is then cleaved to create several active interleukin-8 isoforms.

A 72 amino acid peptide is the primary form secreted by macrophages in culture.

Many receptors on the surface membrane bind to Interleukin-8; the most frequently studied types are the CXCR1 and CXCR2 serpentine receptors coupled to a G protein. Interleukin-8 expression and affinity differ between the two receptors (CXCR1> CXCR2).

Through a chain of biochemical reactions, interleukin-8 is secreted and is an essential mediator of the immune response in the response of the innate immune system.

Interleukin 9

Interleukin 9, also known as IL-9, is a pleiotropic cytokine (cell signaling molecule) that belongs to the group of interleukins.

Interleukin-9 is produced by various cells, such as mast cells, natural killer T, Th2, Th17, Treg, type 2 cells, innate lymphoid cells, and Th9 cells in varying amounts. Th9 cells are considered the central CD4 + T cells that produce Interleukin-9.

Interleukin 10

Interleukin 10 (IL-10) is a protein that inhibits the synthesis of several cytokines, including IFN-gamma, interleukin-2, interleukin-3, tumor necrosis factor, and granulocyte-macrophage colony-stimulating factor produced by activated macrophages and by helper T cells.

In structure, Interleukin-10 is a protein of approximately 160 amino acids that contains four conserved cysteines involved in disulfide bonds.

Interleukin-10 is very similar to the BCRF1 protein from human herpesvirus 4 (Epstein-Barr virus), inhibiting the gamma-interferon synthesis and the equine herpesvirus 2 (equine herpes 2) protein E7.

It is also similar, but to a lesser degree, to the human protein mda-7. A protein that has antiproliferative properties in human melanoma cells. Mda-7 contains only two of the four cysteines of Interleukin-10.

Interleukin 11

Interleukin 11 (IL-11) is a protein that in humans is encoded by the Interleukin11 gene.

Interleukin-11 is a multifunctional cytokine first isolated in 1990 from bone marrow-derived stromal cells.

It is a crucial regulator of multiple events in hematopoiesis, especially the stimulation of megakaryocyte maturation. It is also known as adipogenesis inhibitory factor (AGIF) and oprelvekin.

The human Interleukin-11 gene, consisting of 5 exons and four introns, is located on chromosome 19 and encodes a 23 kDa protein. Interleukin-11 is a member of the Interleukin-6 family of cytokines, distinguished by its use of the common gp130 co-receptor.

The Interleukin-11Rα subunit provides the specificity of the signal.

Interleukin 12

Interleukin 12 (IL-12) is a disulfide-linked heterodimer consisting of 35 kDa alpha and 40 kDa beta subunits.

It is involved in the stimulation and maintenance of Th1 cellular immune responses, including the defense of the regular host against various intracellular pathogens, such as Leishmania, Toxoplasma, measles virus, and human immunodeficiency virus 1 (HIV).

Interleukin-12 also has a vital role in enhancing the cytotoxic function of NK cells and the position in pathological Th1 responses, such as in inflammatory bowel disease and multiple sclerosis. Suppression of Interleukin-12 activity in such conditions may have therapeutic benefits.

On the other hand, the administration of recombinant Interleukin-12 may have a therapeutic benefit in conditions associated with pathological Th2 responses.

Interleukin 13

Interleukin 13 (IL-13) is a protein that in humans is encoded by the Interleukin13 gene. Interleukin-13 was first cloned in 1993 and is found on chromosome 5q31 with a length of 1.4 kb.

It has a mass of 13 kDa and folds into four alpha-helical bundles. The secondary structural characteristics of Interleukin-13 are similar to those of Interleukin 4 (IL-4); however, it only has 25% sequence homology to Interleukin-4 and is capable of Interleukin-4 independent signaling.

Interleukin-13 is a cytokine secreted by T helper type 2 (Th2) cells, CD4 cells, natural killer T cells, mast cells, basophilic cells, eosinophilic cells, and Nuocyte cells.

Interleukin-13 is a central regulator in IgE synthesis, goblet cell hyperplasia, mucus hypersecretion, airway hyperresponsiveness, fibrosis, and upregulation of chitinase. It is a mediator of allergic inflammation and different diseases, including asthma.

Interleukin 14

Alpha-taxilin, also known as interleukin-14 (IL-14) or high molecular weight B-cell growth factor (HMW-BCGF), is a protein that in humans is encoded by the TXLNA gene.

Interleukin-14 is a cytokine that controls the growth and proliferation of both standard and cancer B cells. This molecule was also recently designated taxi.

Interleukin 14 induces B cell proliferation, inhibits antibody secretion, and expands selected B cell subsets. This interleukin is produced mainly by T cells and specific malignant B cells.

Interleukin 15

Interleukin 15 (IL-15) is a cytokine that possesses various biological functions, including the stimulation and maintenance of cellular immune responses.

Interleukin-15 stimulates T lymphocyte proliferation, which requires the interaction of Interleukin-15 with components of Interleukin-2R, including Interleukin-2R beta and probably Interleukin-2R gamma, but not Interleukin-2R alpha.

Interleukin 16

Pro-interleukin-16 is a protein that in humans is encoded by the IL16 gene. This gene was discovered in 1982 at Boston University by Dr. David Center and Dr. William Cruikshank.

The protein encoded by this gene is a pleiotropic cytokine that functions as a chemoattractant, a modulator of T-cell activation, and an inhibitor of HIV replication.

CD4 mediates the signaling process of this cytokine. The product of this gene undergoes proteolytic processing, which is obtained to produce two functional proteins.

The function of cytokines is attributed exclusively to the secreted C-terminal peptide, while the N-terminal product may play a role in cell cycle control.

Caspase 3 is reported to be involved in the proteolytic processing of this protein. Two alternately spliced ​​transcript variants encoding different isoforms have been reported.

Interleukin 16 is a cytokine released by various cells (including lymphocytes and some epithelial cells) characterized as a chemoattractant for specific immune cells that express the CD4 cell surface molecule.

IL-16 was initially described as a factor that could attract activated T cells in humans, previously called lymphocyte chemoattractant (LCF).

Since then, this interleukin has been shown to recruit and activate many other cells that express the CD4 molecule, including monocytes, eosinophils, and dendritic cells.

The structure of Interleukin 16 was determined after its cloning in 1994. This cytokine is produced as a precursor peptide (pro-IL-16) that requires processing by an enzyme called caspase-3 to activate. CD4 is the cell signaling receptor for mature Interleukin 16.

Interleukin 17

Interleukin 17A (IL-17 or IL-17A) is a pro-inflammatory cytokine. This cytokine is produced by a group of helper T cells known as helper T cells 17 in response to its stimulation with Interleukin-23.

Initially, Th17 was identified in 1993 by Rouvier et al., who isolated the Interleukin17 transcript from a rodent T-cell hybridoma.

The protein encoded by Interleukin17A is a founding member of the Interleukin-17 family. The Interleukin17 protein exhibits high homology to a viral protein similar to interleukin 17 encoded in the T-lymphotropic rhadinovirus Herpesvirus saimiri genome. In rodents, Interleukin-17 is often referred to as CTLA8.

Biologically active Interleukin-17 interacts with the type I cell surface receptor Interleukin-17R. In turn, there are at least three variants of Interleukin-17R called Interleukin17RA, Interleukin17RB and Interleukin17RC.

After binding to the receptor, interleukin-17 activates several signaling cascades that, in turn, lead to the induction of chemokines.

Acting as chemoattractants, these chemokines recruit immune cells, such as monocytes and neutrophils, to the site of inflammation. Typically, the signaling events mentioned above follow pathogens’ invasion of the body.

Promoting inflammation, Interleukin-17 works in concert with tumor necrosis factor and interleukin-1. In addition, activation of Interleukin-17 signaling is often seen in the pathogenesis of various autoimmune disorders, such as psoriasis.

Interleukin 18

Interleukin-18 (IL18, also known as interferon-gamma inducing factor) is a protein that in humans is encoded by the IL18 gene. The protein encoded by this gene is a pro-inflammatory cytokine.

Interleukin 18 is a cytokine that belongs to the IL-1 superfamily produced by macrophages and other cells.

Interleukin 18 works by binding to the interleukin-18 receptor and, together with IL-12, induces cell-mediated immunity after infection with microbial products such as lipopolysaccharide (LPS).

After stimulation with Interleukin 18, natural killer (NK) cells and specific T cells release another important cytokine called interferon-γ (IFN-γ) or type II interferon that plays a vital role in the activation of macrophages or other cells.

Combining this cytokine and IL12 has been shown to inhibit IL-4-dependent IgE and IgG1 production and enhance IgG2a production in B cells.

Interleukin 18 binding protein (IL18BP) can interact with this cytokine and, therefore, negatively regulate its biological activity.

Interleukin 19

Interleukin 19 (IL19) is a protein that in humans is encoded by the IL19 gene. The protein encoded by this gene is a cytokine that belongs to the IL-10 subfamily of cytokines.

This cytokine is found to be preferentially expressed on monocytes. It can bind to the interleukin-20 receptor complex and lead to activation of the signal transducer and activator of transcription 3 (STAT3).

A similar cytokine in the mouse is reported to positively regulate IL6 and TNF-alpha expression and induce apoptosis, suggesting a role for this cytokine in inflammatory responses. Alternatively, spliced ​​transcript variants encoding the various isoforms have been described.

Interleukin-19 is a cytokine that belongs to the IL-10 family of cytokines and other interleukins, including IL-10, IL-20, IL-22, IL-24, IL-26, and various virus-encoded cytokines.

It signals through the same cell surface receptor (IL-20R) used by IL-20 and IL-24. The IL-19 gene is expressed in resting monocytes and B cells.

It is upregulated in monocytes after stimulation with granulocyte-macrophage colony-stimulating factor (GM-CSF), lipopolysaccharide, or Pam3CSK4.

Interleukin 20

Interleukin 20 (IL20) is a protein that in humans is encoded by the IL20 gene. Interqueukin 20 also includes other cytokines, including IL-19, IL-20, IL-22, IL-24, and IL-26.

Based on the common structural and functional properties of IL-20 receptors and target cells, these cytokines constitute the same subfamily, Interleukin 20.

The protein encoded by this gene is a cytokine structurally related to interleukin 10 (IL-10). This cytokine has been shown to transduce its signal through signal transducer and activator of transcription 3 (STAT3) in keratinocytes.

A specific receptor for this cytokine is expressed in the skin and is dramatically regulated in psoriatic skin, suggesting a role for this protein in epidermal function and psoriasis.

Interleukin 20 is a protein that belongs to the IL-10 family of cytokines. Interleukin 20 is produced by activated keratinocytes and monocytes and transmits an intracellular signal through two distinct cell surface receptor complexes on keratinocytes and other epithelial cells.

Interleukin 20 regulates the proliferation and differentiation of keratinocytes during inflammation, particularly inflammation associated with the skin. Furthermore, interleukin 20 also causes cell expansion of multipotential hematopoietic progenitor cells.

Interleukin 21

Interleukin 21 (IL-21) is a protein that in humans is encoded by the IL21 gene.

Interleukin-21 is a cytokine that has powerful regulatory effects on cells of the immune system, including natural killer cells and cytotoxic T cells that can kill infected or cancer cells. This cytokine induces cell division/proliferation in its target cells.

Interleukin 22

Interleukin-22 (IL-22) is a protein that in humans is encoded by the IL22 gene. Interleukin-22 is a member of a group of cytokines called the IL-10 family or IL-10 superfamily (including IL-19, IL-20, IL-24, and IL-26), a class of potent mediators of cellular inflammatory responses.

It shares the use of IL-10R2 in cell signaling with other members of this family, IL-10, IL-26, IL-28A / B, and IL-29.

Interleukin 22 is produced by activated NK and T cells and initiates innate immune responses against bacterial pathogens, especially in epithelial cells such as intestinal and respiratory epithelial cells.

Interleukin 22, along with IL-17, is rapidly produced by LTi-like spleen cells and is also produced by Th17 cells and probably plays a role in the coordinated response of innate adaptive immune systems, autoimmunity, and tissue regeneration.

The biological activity of interleukin 22 is initiated by binding to a cell surface complex composed of IL-22R1 and IL-10R2 receptor chains and further regulated by interactions with a soluble binding protein, IL-22BP, that shares sequence similarity with an extracellular region of IL -22R1 (SIL-22R1).

Interleukin 22 and IL-10 receptor chains play a role in cell targeting and signal transduction to selectively initiate and regulate immune responses.

Interleukin 22 can contribute to immune disease by stimulating inflammatory responses, S100, and defensins. Interleukin 22 also promotes the survival of hepatocytes in the liver and epithelial cells in the lung and intestine, similar to IL-10.

In some contexts, the pro-inflammatory versus tissue-protective functions of interleukin 22 is regulated by the frequently co-expressed IL-17A cytokine.

Interleukin 23

Interleukin-23 (IL-23) is a heterodimeric cytokine composed of an IL12B subunit (IL-12p40) (which is shared with IL12) and the IL23A subunit (IL-23p19). A functional receptor for interleukin 23 (the IL-23 receptor) has been identified and is composed of IL-12Rβ1 and IL-23R.

Before discovering Interleukin 23, IL-12 had been proposed to represent a key mediator of inflammation in mouse models of inflammation. However, many studies aimed at evaluating the role of IL-12 had blocked IL-12p40 activity and therefore were not as specific as thought.

Studies that blocked the IL-12p35 function did not produce the same results as those targeting IL-12p40 as expected if both subunits were part of IL-12 only. The discovery of an additional binding partner potential for IL-12p40 led to a re-evaluation of this role for IL-12.

Seminal studies in experimental autoimmune encephalomyelitis, a murine model of multiple sclerosis, showed that interleukin 23 was responsible for the observed inflammation, not IL-12, as previously thought.

Subsequently, IL-23 was shown to facilitate the development of inflammation in many other models of immune pathology in which IL-12 had been previously implicated, including models of arthritis, intestinal inflammation, and psoriasis.

Interleukin 24

Interleukin 24 (IL-24) is a protein that in humans is encoded by the IL24 gene.

Interleukin 24 is a cytokine belonging to the IL-10 family of cytokines that communicates through two heterodimeric receptors: IL-20R1 / IL-20R2 and IL-22R1 / IL-20R2. This interleukin is also known as melanoma differentiation-associated 7 (mda-7) due to its discovery as a tumor suppressor protein.

Interleukin 24 appears to control cell survival and proliferation by inducing rapid activation of particular transcription factors called STAT1 and STAT3.

This cytokine is predominantly released by activated monocytes, macrophages, and T helper 2 (Th2) cells and acts on non-hematopoietic tissues such as skin, lung, and reproductive tissues. Interleukin 24 plays a vital role in wound healing, arthritis, psoriasis, and cancer.

Several studies have shown that cell death occurs in cancer cells/cell lines after exposure to interleukin 24. The IL-24 gene is located on chromosome 1 in humans.

Interleukin 25

Interleukin 25 (IL-25), also known as interleukin-17E (IL-17E), is a protein that in humans is encoded by the IL25 gene.

Interleukin 25 is a cytokine that shares sequence similarity with IL-17. This cytokine can induce NF-κB activation and stimulate IL-8 production. Both this cytokine and IL17B are ligands for the IL17RB cytokine receptor.

Studies of a similar gene in mice suggested that this cytokine could be a pro-inflammatory cytokine that favors the Th2-type immune response. Two alternately spliced ​​transcript variants of this gene encoding different isoforms have been reported.

Interleukin-25 is a cytokine that belongs to the IL-17 family of cytokines and is secreted by T helper type 2 (Th2) cells and mast cells.

Interleukin 26

Interleukin-26 (IL-26) is a protein that in humans is encoded by the IL26 gene.

Interleukin 26 is a 171 amino acid protein similar in amino acid sequence to interleukin 10. It was initially called AK155 and is composed of a signal sequence, six helices, and four conserved cysteine ​​residues.

Interleukin 26 is expressed on certain herpesvirus transformed T cells but not on primary stimulated T cells. Interleukin 26 sends signals through a receptor complex that comprises two different proteins called IL-20 receptor one and IL-10 2.

By signaling through this receptor complex, interleukin 26 induces the rapid phosphorylation of the transcription factors STAT1 and STAT3, which enhance IL-10 and IL-8 secretion and express the CD54 molecule on the surface of cells. Epithelial.

Interleukin 27

Interleukin 27 (IL-27) is a member of the IL-12 family of cytokines. It is a heterodimeric cytokine composed of two genes, gene three induced by the Epstein-Barr virus (EBI3) and IL-27p28.

Interleukin 27 is expressed by antigen-presenting cells and interacts with a specific cell surface receptor complex known as interleukin 27 receptor (IL-27R).

This receptor consists of two proteins, IL-27ɑ and gp130. Interleukin 27 induces the differentiation of various T cell populations in the immune system and positively regulates IL-10.

Interleukin 28

Interleukin-28 (IL-28) is a cytokine that occurs in two isoforms, IL-28A and IL-28B. It plays a role in immune defense against viruses, including inducing an ‘antiviral state’ by activating the Mx. 2 ‘, 5’-oligoadenylate synthetase, and ISGF3G (Interferon Stimulated Gene Factor 3).

IL-28A and IL-28B belong to the type III interferon family of cytokines and are very similar (in amino acid sequence) to IL-29.

Their classification as interferons is due to their ability to induce an antiviral state, while their further classification as cytokinesis due to their chromosomal location, as well as the fact that they are encoded by multiple exons, as opposed to a single exon, such as they are the majority of type-I interferons.

Interleukin 29

Interleukin-29 (IL-29) is a protein that in humans is encoded by the IL29 gene that resides on chromosome 19.

Interleukin 29 is a member of the spiral cytokine family and is a type III interferon. It is also known as IFNλ1 and is very similar in amino acid sequence to IL-28, the other type of interferon III.

Interleukin 29 plays a vital role in host defenses against microbes, and its gene is highly upregulated in virus-infected cells. Interleukin 29 is not present in the mouse genome.

Interleukin 30

Interleukin-30 (IL-30) is a protein with a molecular weight of 28 kilodaltons, forming a heterodimeric cytokine chain called interleukin 27 (IL-27), which is why it is sometimes referred to as IL27-p28.

The other chain of IL-27 is a molecule called Epstein-Barr induced gene-3 (EBI3). Interleukin 30 is a member of the long-chain 4-helix packet cytokine family. Thus it is structurally similar to IL-6.

This gene for this molecule is now officially called IL-27 under the gene nomenclature committee guidelines.

Interleukin 31

Interleukin-31 (IL-31) is a protein that in humans is encoded by the IL31 gene that resides on chromosome 12. Interleukin 31 is an inflammatory cytokine that helps activate cell-mediated immunity against pathogens.

It has also been a significant player in several chronic inflammatory diseases, including atopic dermatitis.

Interleukin 31 is produced by various cells, namely T-helper cells type 2 (TH2). Interleukin 31 sends signals through a receptor complex composed of IL-31RA, and oncostatin M receptor β (OSMRβ) expressed in immune and epithelial cells.

These signals activate ERK1 / 2 MAP kinase, PI3K / AKT, and JAK1 / 2 signaling pathways.

Interleukin 32

Interleukin 32 (Il32) is a protein that in humans is encoded by the IL32 gene. This gene encodes a member of the cytokine family.

The protein contains:

  • A tyrosine sulfation site.
  • Three potential N-myristoylation sites.
  • Multiple putative phosphorylation sites.
  • An RGD cell-binding sequence.

The expression of this protein increases after activation of T cells by mitogens or activation of NK cells by IL-2. This protein induces the production of TNF-alpha from macrophage cells. Alternative transcriptional splice variants encoding different isoforms have been characterized.

Interleukin 32 is a pro-inflammatory cytokine that can induce immune system cells (such as monocytes and macrophages) to secrete inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) and IL-6. Furthermore, it can also induce the production of chemokines such as IL-8 and MIP-2 / CXCL2.

Interleukin 32 may also support osteoclast differentiation but not osteoclast activation by regulating the MAPK / ERK pathway and the actin cytoskeleton.

Interleukin 33

Interleukin 33 (IL-33) is a protein that in humans is encoded by the IL33 gene. Interleukin 33 is a member of the IL-1 family that potently drives the production of T helper-2 (Th2) associated cytokines (e.g., IL-4).

Interleukin 33 is a ligand for ST2 (IL1RL1), a receptor of the IL-1 family that is highly expressed in Th2 cells, mast cells, and innate group 2 lymphocytes.

Interleukin 33 is expressed by various cell types, including fibroblasts, mast cells, dendritic cells, macrophages, osteoblasts, endothelial cells, and epithelial cells.

Interleukin 34

Interleukin 34 (IL-34) is a protein that belongs to a group of cytokines called interleukins. It was initially identified in humans by large-scale screening for secreted proteins; Chimp, murine, rat, and chicken interleukin 34 orthologs have also been found.

Protein comprises 241 amino acids, 39 kilodaltons by mass, and forms homodimers.

Interleukin 34 increases the growth or survival of immune cells known as monocytes; It triggers its activity by binding the receptor for colony-stimulating factor 1.

Human interleukin 34 messenger RNA (mRNA) expression is most abundant in the spleen but occurs in other tissues: thymus, liver, small intestine, colon, prostate, lung, heart, brain, kidney, testes, and ovary.

The discovery of the protein Interleukin 34 in the red pulp of the spleen suggests participation in the growth and development of myeloid cells, consistent with its activity in monocytes.

Interleukin 35

Interleukin 35 (IL-35) is an IL-12 family cytokine produced by regulatory, but not effector, T cells and plays a role in immune suppression.

It is a dimeric protein composed of IL-12α and IL-27β chains, which are encoded by two separate genes called IL12A and EBI3, respectively.

Secreted by regulatory T cells (Tregs), interleukin 35 suppresses the inflammatory responses of immune cells.

Interleukin 35 is not constitutively expressed in tissues, but the gene encoding interleukin 35 is transcribed by vascular endothelial cells, smooth muscle cells, and monocytes after activation with pro-inflammatory stimuli.

Studies in mice show the absence of any Interleukin 35 chains of regulators.

Regulatory T cells reduce the cells’ ability to suppress inflammation; This has been observed during cell culture experiments and the use of an experimental model for inflammatory bowel disease.

To produce its suppressive effects (e.g., in collagen-induced arthritis), interleukin 35 has selective activities on different subsets of T cells; it induces proliferation of regulatory T cell populations but reduces the activity of Th17 cell populations.

Interleukin 36

In humans, there are four different genes for interleukin-36. There are three receptor agonists: IL36A, IL36B, and IL36G, and an antagonist IL36RA receptor bind to the Interleukin 36 receptor (IL1RL2 / IL-1Rrp2 / IL Interleukin 36 receptor) with variable affinities.

Agonists are known to activate NF-κB (activated B cell kappa light chain enhancing nuclear factor) and mitogen-activated protein kinases to induce various pro-inflammatory mediators.

It has also been found to activate T cell proliferation and IL-2 release. Due to their predominant expression in epithelial tissues, interleukin 36 cytokines are believed to play an essential role in the pathogenesis of skin diseases, especially psoriasis.