Interleukin 5 (IL5) is an
interleukin produced by type-2
T helper cells and
mast cells.
Function
Through binding to the
interleukin-5 receptor, interleukin 5 stimulates
B cell
B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted or ...
growth and increases
immunoglobulin
An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...
secretion - primarily
IgA Iga may refer to:
Arts and entertainment
* Ambush at Iga Pass, a 1958 Japanese film
* Iga no Kagemaru, Japanese manga series
* Iga, a set of characters from the Japanese novel '' The Kouga Ninja Scrolls''
Biology
* ''Iga'' (beetle), a gen ...
. It is also a key mediator in
eosinophil activation.
Structure
IL-5 is a 115-
amino acid (in human, 133 in the mouse) -long TH2
cytokine that is part of the hematopoietic family. Unlike other members of this
cytokine family (namely
interleukin 3 and
GM-CSF), this glycoprotein in its active form is a homodimer.
Tissue expression
The IL-5
gene is located on
chromosome 11 in the mouse, and 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
Immunohistochemistry (IHC) is the most common application of immunostaining. It involves the process of selectively identifying antigens (proteins) in cells of a tissue section by exploiting the principle of antibodies binding specifically to an ...
.
IL-5 expression is regulated by several
transcription factors including
GATA3.
Clinical significance
Interleukin-5 has long been associated with the cause of several allergic diseases including
allergic rhinitis and
asthma, wherein a large increase in the number of circulating, airway tissue, and induced
sputum
Sputum is mucus that is coughed up from the lower airways (the trachea and bronchi). In medicine, sputum samples are usually used for a naked eye examination, microbiological investigation of respiratory infections and cytological investigations ...
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.
Drugs that target IL-5 are
mepolizumab and
reslizumab.
Effect 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
Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are an immune cell or some types of venom, e.g. from the puff adder (''Bitis arietans'') or brown recluse spider (''Loxosceles reclusa'').
Cell physiology
Treating cells ...
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.
Mepolizumab is a monoclonal antibody antagonist IL-5 which can reduce excessive eosinophilia.
In
Hodgkin lymphoma, for instance, the typically-observed
eosinophilia
Eosinophilia is a condition in which the eosinophil count in the peripheral blood exceeds . Hypereosinophilia is an elevation in an individual's circulating blood eosinophil count above 1.5 x 109/ L (i.e. 1,500/μL). The hypereosinophilic syndro ...
is thought to be attributable to an increased production of IL-5.
Interactions
Interleukin 5 has been shown to
interact 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 (IL3) 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.
References
External links
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Interleukins