Interleukin 15(IL-15)

Interleukin-15 (IL-15) is a protein that plays a role in regulating the immune system.

It is important for the development and function of natural killer cells and certain T cells.

IL-15 also has roles in promoting the proliferation and survival of these immune cells.

IL-15 is an inflammatory cytokine with structural similarity to Interleukin-2 (IL-2). 

It is encoded by the IL15 gene. 

Like IL-2, IL-15 binds to and signals through a complex composed of IL-2/IL-15 receptor beta chain (CD122) and the common gamma chain (gamma-C, CD132). 

IL-15 is secreted by mononuclear phagocytes and other cells following infection by viruses.

This cytokine induces the proliferation of natural killer cells, part of  the innate immune system whose principal role is to kill virally infected cells.

IL-15 is characterized as T cell growth factor.

IL-15 is expressed by a large number of cell types and tissues, including monocytes, macrophages, dendritic cells (DC), keratinocytes, fibroblasts, myocyte and nerve cells.

It is a pleiotropic cytokine, playing an important role in innate and adaptive immunity.

IL-15 is a glycoprotein encoded by the chromosome 4q31

IL-15 mRNA can be found in many cells and tissues including mast cells, cancer cells or fibroblasts.

IL-15 cytokine is produced as a mature protein mainly by dendritic cells, monocytes and macrophages. 

Expression of IL-15 can be stimulated by cytokine such as GM-CSF, mRNA, CpG oligonucleotides, lipopolysaccharide , interferon gamma (IFN-γ) or after infection of monocytes by herpes virus, Mycobacterium tuberculosis and Candida albicans.

IL-15 regulates the activation and proliferation of T and natural killer (NK) cells. 

Survival signals that maintain memory T cells in the absence of antigen are provided by IL-15. 

IL-15 is also implicated in NK cell development. 

In humans with celiac disease IL-15 similarly suppresses apoptosis in T-lymphocytes.

A hematopoietin receptor-IL-15 receptor, binds IL-15 to propagate its function. 

The IL-15 receptor in common with the receptor nterleukin 2 (IL-2) allowing both cytokines to compete for and negatively regulate each other’s activity. 

CD8+ memory T cell number is controlled by a balance between IL-15 and IL-2. 

When IL-15 binds its receptor, JAK kinase, STAT3, STAT5, and STAT6 transcription factors are activated to elicit downstream signaling events.

IL-15 and its receptor subunit alpha (IL-15Rα) are also produced by skeletal muscle in response to different exercises, playing significant roles in visceral fat reduction and myofibrillar protein synthesis.

Suppression of IL-15 may be a potential treatment for celiac disease and even presents the possibility of preventing its development. 

IL-15 promotes non-alcoholic fatty liver disease.

IL-15 present in the synovial tissue of patients diagnosed with rheumatoid arthritis. 

IL-15  is associated  collagen-induced arthritis.

IL-15 SA is currently being evaluated for antiviral and anticancer activities, in addition to enhancing immunotherapy and vaccines.

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