Expression of the extracellular region of the human interleukin-4 receptor α chain and interleukin-13 receptor α1 chain by a silkworm–baculovirus system

The receptor binding to interleukin (IL)-13 is composed of the IL-13 receptor α1 chain (IL-13Rα1) and the IL-4 receptor α chain (IL-4Rα). In order to investigate the interaction of IL-13 with IL-13Rα1 and IL-4Rα, the DNA fragments coding the extracellular regions of human IL-13Rα1 and the IL-4Rα (containing a cytokine receptor homologous region) were fused with mouse Fc and expressed by a silkworm–baculovirus system. The expressed receptors were successfully purified by affinity chromatography using protein A, and the Fc region was removed by thrombin digestion. After further purification with anion-exchange chromatography, these receptors were used to investigate the ligand–receptor interaction. Size exclusion chromatography and SPR analysis revealed that mixture of IL-13 and IL-13Rα1 showed predominant affinity to IL-4Rα, although neither detectable affinity of IL-13 nor IL-13Rα1 was observed against IL-4Rα. Combining these data with the moderate affinity of IL-13 to IL-13Rα1, this indicates that IL-13 first binds to IL-13Rα1 and recruits consequently to IL-4R.