Other Interleukins & Receptors

Interleukins & receptors can be mainly classified into subfamilies: IL-1 family, IL-6 family, IL-10 family, IL-17 family and common γ-chain family. The rest of other interleukins also play key roles in cell growth, differentiation, and motility. They are important in stimulating immune responses, such as inflammation and hematopoiesis.

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Other Interleukins & Receptors Background

Th2-like cytokines

Interleukin-5 (IL-5) was initially described as an eosinophil and B-cell growth factor. Its receptor shares the β-chain (CD131) with IL-3 and GM-CSF. IL-5 promotes proliferation, activation, differentiation, survival, and adhesion of eosinophils.

Interleukin-13 (IL-13) is a 4-helix bundle protein expressed by activated Th2 cells, mast cells, basophils, eosinophils, and NKT cells. Its receptors are IL-13RA1 and IL-13RA2, and signaling occurs via the IL-4 receptor complex type II, which consists of IL-4RA and IL-13RA1. IL-13RA2 inhibits IL-13 and has been linked to fibrosis. IL-13 activates the same signal transduction pathways as IL-4 and induces IgE production.

Interleukins with chemokine activity

Interleukin-8 (IL-8) was identified as a neutrophil-specific chemotactic factor and later classified as a member of the CXC chemokine family. IL-8 is produced by a variety of cells, such as monocytes and macrophages, neutrophils, lymphocytes, and endothelial and epithelial cells after stimulation with IL1A, IL1B, IL-17, TNF-alpha or TLRs. The receptors for IL-8 are CXCR1 (IL-8RA) and CXCR2 (IL-8RB). The major effector functions of IL-8 are activation and recruitment of neutrophils to the site of infection or injury.

Interleukin-16 (IL-16) was discovered as a T-cell–specific chemoattractant. IL-16 mediates its biological activity via CD4. IL-16 inhibits T-cell proliferation, promotes Th1-mediated responses, and reduces Th2-mediated inflammation by activating the release of TNF-alpha, IL1B, and IL-15 and concomitantly inhibiting the production of IL-4 and IL-5.

Other interleukins

Interleukin-13 (IL-3) is expressed by T cells, macrophages, stromal cells, NK cells, mast cells, and eosinophils. Because IL-3, IL-5, and GM-CSF share a common receptor subunit β-chain (CD131), their functions partially overlap. On binding IL-3, the β-chain forms a heterodimer with the cytokine-specific α-chain. IL-3 is a multilineage hematopoietic growth factor during early stages of hematopoiesis, in synergy with other cytokines.

Interleukin-14 (IL-14) known as alpha-taxilin or high molecular weight B-cell growth factor (HMW-BCGF) is a protein that in humans is encoded by the TXLNA gene.Two transcripts are produced from opposite strands of the IL-14 gene, termed IL-14α and IL-14β. IL-14 is produced by T cells and B-lineage and T-lineage lymphoma cell lines.

Interleukin-32 (IL-32) are mainly expressed by activated T cells and NK cells. Epithelial cells express IL-32 on stimulation with TNF-alpha, IFN-γ, IL1B, and IL-18. IL-32 is highly expressed in synovial tissue samples from patients with rheumatoid arthritis (RA), and expression levels are associated with disease severity.

Interleukin-34 (IL-34), also known as C16orf77, is secreted as a homodimer of 39-kd monomers. IL-34 is expressed in various tissues, including the heart, brain, liver, kidney, spleen, thymus, testes, ovary, small intestine, prostate, and colon, and is most abundant in the spleen. The receptor for IL-34 is colonystimulating factor (CSF)–1R. IL-34 stimulates monocyte proliferation.