Interleukin 36, or IL-36, is a group of

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 autocrin ...

s in the IL-1 family with

pro-inflammatory Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molecu ...

effects. The role of IL-36 in inflammatory diseases is under investigation. There are four members of the IL-36 family which bind to the IL-36 receptor ( IL1RL2/IL-1Rrp2/IL-36 receptor dimer) with varying affinities.

IL36A Interleukin-36 alpha also known as interleukin-1 family member 6 (IL1F6) is a protein that in humans is encoded by the ''IL36A'' gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian ...

, IL36B, and IL36G are IL-36 receptor agonists. IL36RA is an IL-36 receptor antagonist, inhibiting IL-36R signaling. The agonists are known to activate

NF-κB Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is a protein complex that controls transcription of DNA, cytokine production and cell survival. NF-κB is found in almost all animal cell types and is involved in cellular ...

, mitogen-activated protein kinases, Erk1/2 and

JNK c-Jun N-terminal kinases (JNKs), were originally identified as kinases that bind and phosphorylate c-Jun on Ser-63 and Ser-73 within its transcriptional activation domain. They belong to the mitogen-activated protein kinase family, and ar ...

through IL-36R/IL-1RAcP, which targets the IL-8 promotor and results in IL-6 secretion and induces various proinflammatory mediators. Binding of the IL-36R agonists to IL-1Rrp2 recruits

IL-1RAcP Interleukin-1 receptor accessory protein is a protein that in humans is encoded by the ''IL1RAP'' gene. Interleukin 1 induces synthesis of acute phase and proinflammatory proteins during infection, tissue damage, or stress, by forming a complex a ...

, activating the signaling pathway. IL-36Ra binds to IL-36R, preventing the recruitment of IL-1RAcP.

Function

IL-36 has been found to activate

T cell A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...

proliferation and release of

IL-2 The Ilyushin Il-2 (Russian: Илью́шин Ил-2) is a ground-attack plane that was produced by the Soviet Union in large numbers during the Second World War. The word ''shturmovík'' ( Cyrillic: штурмовик), the generic Russian term ...

. Before the functions of the IL-36 cytokines were determined, they were named as derivatives of IL-1F; they were renamed to their current designations in 2010. Due to their predominant expression in epithelial tissues, IL-36 cytokines are believed to play a significant role in the pathogenesis of skin diseases, especially that of

psoriasis Psoriasis is a long-lasting, noncontagious autoimmune disease characterized by raised areas of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small, localized patches to complete ...

. IL-36 has also been linked to

psoriatic arthritis Psoriatic arthritis is a long-term inflammatory arthritis that occurs in people affected by the autoimmune disease psoriasis. The classic feature of psoriatic arthritis is swelling of entire fingers and toes with a sausage-like appearance. Th ...

, systemic lupus erythematosus, inflammatory bowel disease,

ulcerative colitis Ulcerative colitis (UC) is a long-term condition that results in inflammation and ulcers of the colon and rectum. The primary symptoms of active disease are abdominal pain and diarrhea mixed with blood (hematochezia). Weight loss, fever, and ...

, Crohn's disease, and Sjögren's syndrome. IL-36 must be cleaved at the N-terminus to become active, probable enzymes mediating the activation could be

neutrophil granule Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying ...

-derived

protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...

elastase In molecular biology, elastase is an enzyme from the class of ''proteases (peptidases)'' that break down proteins. In particular, it is a serine protease. Forms and classification Eight human genes exist for elastase: Some bacteria (includin ...

, and

cathepsin G Cathepsin G is a protein that in humans is encoded by the ''CTSG'' gene. It is one of the three serine proteases of the chymotrypsin family that are stored in the azurophil granules, and also a member of the peptidase S1 protein family. Cathepsin ...

, although they may activate the cytokines differentially. IL-36 is expressed by many cells types, most predominantly

keratinocytes Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the basal layer (''stratum basale'') of the skin are sometimes referre ...

respiratory epithelium Respiratory epithelium, or airway epithelium, is a type of ciliated columnar epithelium found lining most of the respiratory tract as respiratory mucosa, where it serves to moisten and protect the airways. It is not present in the vocal cords o ...

, various

nervous tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain ...

, and

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 ...

Genes and expression

The genes encoding for the IL-36 cytokines are found on

chromosome 2 Chromosome 2 is one of the twenty-three pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 2 is the second-largest human chromosome, spanning more than 242 million base pairs and representing almost e ...

q14.1. All three are located in a

cluster may refer to: Science and technology Astronomy * Cluster (spacecraft), constellation of four European Space Agency spacecraft * Asteroid cluster, a small asteroid family * Cluster II (spacecraft), a European Space Agency mission to study t ...

with other members of IL-1 family and the gene order from

centromere The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers ...

telomere A telomere (; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Although there are different architectures, telomeres, in a broad sense, are a widespread genetic feature mos ...

is ''IL-1A-IL-1B-IL-37-IL-36G-IL-36A-IL-36B-IL-36RN-IL1F10-IL-1RN'', and only ''IL-1A'', ''IL''-''1B'' and ''IL-36B.'' All of them probably arose from a common ancestral gene, which is most likely a primordial IL-1 receptor antagonist gene. All three genes are mainly expressed in keratinocytes, bronchial epithelium, brain tissue, and monocytes/macrophages. In the epidermis IL-36 cytokine expression is limited to granular layer keratinocytes with little to no expression in basal layer keratinocytes. IL-36Ra is constitutively expressed in keratinocytes, whereas IL-36γ expression in keratinocytes is rapidly induced after stimulation with

TNF 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 ...

or PMA (Phorbol 12-myristate 13-acetate).

Clinical significance

IL-36-alpha functions primarily in skin and demonstrates increased expression in psoriasis. In addition, decreased expression of this gene has been linked to a poor prognosis in both hepatocellular carcinoma and colorectal cancer patients. IL-36 cytokines may play a regulatory role in the pathogenesis of inflammatory disorders such as

folliculitis Folliculitis is the infection and inflammation of one or more hair follicles. The condition may occur anywhere on hair-covered skin. The rash may appear as pimples that come to white tips on the face, chest, back, arms, legs, buttocks, or head. ...

and eosinophilic pustular folliculitis. In addition, in

acute generalized exanthematous pustulosis Acute generalized exanthematous pustulosis (AGEP) (also known as pustular drug eruption and toxic pustuloderma) is a rare skin reaction that in 90% of cases is related to medication administration. AGEP is characterized by sudden skin eruptions th ...

, IL-36 (mainly IL-36 gamma) was overexpressed in skin lesions. Studies revealed that T cells were sufficient to cause skin inflammation after '' Staphylococcus aureus'' exposure on mice, mediating the skin inflammation via IL-36-controlled, IL-17-dependent T cell responses. IL-36 is significantly involved in the pathogenesis of psoriasis leading to it being targeted therapeutically. Human psoriatic skin plaques displayed elevated IL-36beta. In addition, It was found that serum IL-36 levels are higher in patients with psoriasis vulgaris and its levels positively correlate with disease activity, suggesting that serum IL-36 levels might serve as useful

biomarker In biomedical contexts, a biomarker, or biological marker, is a measurable indicator of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal biological processes, p ...

s in patients with psoriasis.

References

{{Interleukin receptor modulators Interleukins