A relatively newly discovered cytokine that is biologically similar to IL-2. It stimulates T-cell, B-cell and NK-cell proliferation as was previously named IL-T. It is also a chemoactractant for lymphocytes. IL-15 is a 114 amino acids long in it’s mature form. It can be found both secreted and membrane bound.

Receptors to IL-15 have been found on T-cells, B-cells NK cells, and various somatic cells. The IL-15 receptors is composed of 3 subunits. The alpha subunit is specific for IL-15 while the beta and gamma are shared with the IL-2 receptor.

In summary, not much is known about the IL-15 as it has only recently been discovered. It is generally a growth factor for T-cell derived lymphocytes though it has been shown to bind and activate other non-immunological somatic cells. Most of these functions are unknown at present. IL-15 is often assayed in parallel with IL-2, IL-17 and IL-23, as well as other T-cell proliferative cytokines.