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. Author manuscript; available in PMC: 2018 Mar 16.
Published in final edited form as: Math Med Biol. 2018 Mar 14;35(1):79–119. doi: 10.1093/imammb/dqw021

Fig. 1.

Fig. 1

Schematic depiction of IL-2R chains, their intracellular domains and their putative function, assembled based on the literature review. The IL-2R complex is not pre-assembled before IL-2 binding: CD25, IL-2 or CD122 alone (without bound IL-2) have no measurable affinity for CD132; instead, IL-2 is required for the assembly of signalling complex. IL-2 can bind CD25 (low-affinity IL-2R; Kd ≈ 10nM) and CD122 (Kd ≈ 100nM), which, associated with CD132 upon IL-2 binding, form an intermediate affinity IL-2R (Kd ≈ 1nM). When CD25 associated with CD122, it increases IL-2 binding to CD122 approximately 100 fold and this tertiary complex then recruits CD132 to form high affinity IL-2R (Kd 10-50pM) (Wang & Smith, 1987). In the quaternary IL-2R structure, IL-2 makes separate contacts with IL-2Rα (CD25), -β (CD122) and common γ -chain (CD132). CD25 makes no contact with either CD122 or CD132.