Interleukin-2 (IL-2) is a cytokine produced by T-helper cells in response to antigenic or mitogenic stimulation. It is required for T-cell proliferation and other activities crucial to the regulation of the immune response.
IL-2 was discovered to be a member of a family of cytokines, which also includes IL-4, IL-7, IL-9, IL-15 and IL-21. IL-2 signals through a receptor complex consisting of IL-2 specific IL-2 receptor alpha (CD25), IL-2 receptor beta (CD122) and a common gamma chain (γc). All members of this family use the common gamma chain as part of their signaling complex.