Inhibition mechanism of Interleukin-13 (IL-13) signal by extracellular region of IL-13 receptor2 chain

Matsumoto, Fumiko; Hatanaka, Takaaki*; Tamada, Taro; Honjo, Eijiro*; Ota, Shoichiro*; Ito, Yuji*; Izuhara, Kenji*; Kuroki, Ryota

Interleukin-13 (IL-13) is a key cytokine critical to the development of T-cell-mediated humoral immune responses which are associated with allergy and asthma. IL-13 possesses two types of receptor: the heterodimer, composed of IL-13R1 and IL-4R, transducing the IL-13 signals; and the IL-13R2, it has high affinity rather than IL-13R1 against IL-13, acting as a nonsignaling "decoy" receptor. In order to investigate the inhibition mechanism of IL-13 signal by IL-13R2, extra cellular region of IL-13R2 was expressed by silkworm-baculovirus expression system after fusing the DNA cording the extracellular region of human IL-13R2 with the Fc derived from mouse IgG2a. The expressed fusion protein (IL-13R2)2-Fc was purified by a protein A column followed by an ion exchange column. The affinities of the ligand complexes, IL-13/IL-13R1 and IL-13/IL-13R2 to (IL-4R)2-Fc were investigated to explore the inactivation mechanism of the IL-13R1 signal with IL-13R2 by surface plasmon resonance analysis. IL-13/IL-13R1 complex has an affinity (KD=1.2010 M) with (IL-4Ra)2-Fc, whereas the IL-13/IL-13R2 complex had no affinity with (IL-4R)2-Fc. This observation suggests that IL-13R2 does not inactivate the IL-13R1 through formation of a ternary complex with IL-13 and IL-4R, but removes the IL-13 with its higher affinity to IL-13 without forming a ternary complex.