The receptor for IL-2 (IL-2 R) is composed of three subunits, the 55 kDa CD25/IL-2 R alpha chain, the
70 kDa IL-2 R beta chain, and the 65 kDa Common gamma Chain (1, 3). IL-2 first binds to CD25, the
binary complex then recruits IL-2 R beta and gamma c to form the quaternary signaling complex (1, 14). In
addition to IL-2, IL-2 R beta is used by IL-15 in its quaternary signaling complex. gamma c also serves as a
signaling receptor for IL-4, -7, -9, -15, and -21 (1, 3).
In vitro studies have shown an important role for IL-2 in T cell activation and expansion. In vivo,
IL-2 is critical for the development, maintenance and function of regulatory T cells (Treg) which
provide protection against autoimmune disease. On the other hand, IL-2 can also promote
autoimmune inflammation in target organs through its roles in regulating the expression of
T cell trafficking genes, and production of Th2 cytokines. Within the CD8+ T cell subset, IL-2 is
essential for optimal primary responses and differentiation into terminal effector cells. IL-2 also
promotes the development of activated CD8+ T cells into memory cells. (1).
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