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IL-5

Wednesday 24 November 2004

Interleukin 5 or IL-5 is an interleukin produced by T helper-2 cells and mast cells. Its functions are to stimulate B cell growth and increase immunoglobulin secretion. It is also a key mediator in eosinophil activation.

IL-5 is a 115 amino acid (in man, 133 in the mouse) long TH2 cytokine which is part of the hematopoietic family.

Unlike other members of this cytokine family (namely IL-3 and GM-CSF) , in its active form, this glycoprotein is a homodimer.

The IL-5 gene is located on chromosome 11 (in the mouse, chromosome 5 in humans) in close proximity to the genes encoding IL-3, IL-4 and granulocyte-macrophage colony-stimulating factor (GM-CSF) which are often co-expressed in TH2 cells.

Interleukin-5 is also expressed by eosinophils and has been observed in the mast cells of asthmatic airways by immunohistochemistry.

IL-5 expression is regulated by several transcription factors including GATA-3.

Effect of IL-5 on Eosinophils

Eosinophils are terminally differentiated granulocytes found in most mammals.

The principal role of these cells, in a healthy host, is the elimination of antibody bound parasites through the release of 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.

Pathology

Interleukin-5 has long been associated with several allergic diseases including allergic rhinitis and asthma where a large increase in the number of circulating, airway tissue, and induced sputum eosinophil numbers have been observed.

Given the high concordance of eosinophils and, particularly, allergic asthma pathology, it has been widely speculated that eosinophils have an important role in the pathology of this disease.

See also

- interleukins (ILs)