Interleukin 5

Interleukin 5 or IL-5 is an is_associated_with::interleukin produced by T helper-2 cells and is_associated_with::mast cells.

Function
Through binding to the IL-5 receptor, IL-5 stimulates is_associated_with::B cell growth and increases is_associated_with::immunoglobulin secretion. It is also a key mediator in is_associated_with::eosinophil activation.

Structure
IL-5 is a 115-is_associated_with::amino acid (in human, 133 in the mouse) -long TH2 is_associated_with::cytokine that is part of the hematopoietic family. Unlike other members of this is_associated_with::cytokine family (namely IL-3 and is_associated_with::GM-CSF), this glycoprotein in its active form is a homodimer.

Tissue expression
The IL-5 is_associated_with::gene is located on is_associated_with::chromosome 11 in the mouse, and chromosome 5 in humans, in close proximity to the genes encoding IL-3, IL-4, and is_associated_with::granulocyte-macrophage colony-stimulating factor (is_associated_with::GM-CSF), which are often co-expressed in TH2 cells. Interleukin-5 is also expressed by is_associated_with::eosinophils and has been observed in the is_associated_with::mast cells of asthmatic airways by is_associated_with::immunohistochemistry. IL-5 expression is regulated by several is_associated_with::transcription factors including is_associated_with::GATA3.

Clinical significance
Interleukin-5 has long been associated with the cause of several allergic diseases including is_associated_with::allergic rhinitis and is_associated_with::asthma, wherein a large increase in the number of circulating, airway tissue, and induced is_associated_with::sputum eosinophils have been observed. Given the high concordance of eosinophils and, in particular, allergic asthma pathology, it has been widely speculated that eosinophils have an important role in the pathology of this disease.

Effect of IL-5 on Eosinophils
Eosinophils are terminally differentiated is_associated_with::granulocytes found in most is_associated_with::mammals. The principal role of these cells, in a healthy host, is the elimination of antibody bound parasites through the release of is_associated_with::cytotoxic granule proteins. Given that eosinophils are the primary IL-5Rα-expressing cells, it is not surprising that this cell type responds to IL-5. In fact, IL-5 was originally discovered as an eosinophil colony-stimulating factor, is a major regulator of eosinophil accumulation in tissues, and can modulate eosinophil behavior at every stage from maturation to survival. is_associated_with::Mepolizumab is a monoclonal antibody against IL-5 which can reduce excessive eosinophilia.

In Hodgkin lymphoma, for instance, the typically-observed is_associated_with::eosinophilia is thought to be attributable to an increased production of IL-5.

Interactions
Interleukin 5 has been shown to interact with is_associated_with::Interleukin 5 receptor alpha subunit.

Receptors
The IL-5 receptor is composed of an α and a βc chain. The α subunit is specific for the IL-5 molecule, whereas the βc subunit also recognised by interleukin 3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Glycosylation of the Asn196 residue of the Rα subunit appears to be essential for binding of IL-5.