[Function, molecular structure and gene expression of IL-2 and the receptors]

The Interleukin 2 receptor is now assumed to be composed of three chains, the L (alpha or Tac), H (beta) chain and p56. The L chain binds IL-2 with low affinity, whereas intermediate-affinity binding of IL-2 is achieved by an association of p56 and the H chain. The high-affinity IL-2R is therefore believed to be a quaternary complex composed of the L chain, the H chain, p56 and IL-2. A larger number of L chains enhances the association rate of IL-2 to form the high-affinity IL-2R in agreement with the stepwise binding model. The signal transduction-competent H chain has been shown to associate with p56lck upon IL-2 stimulation.