hIL-33 binding to hST2-Fc confirmed by pull down assay. a) pull down of h-IL-33 by hST2-Fc. b) pull down of hST2-Fc by h-IL-33-His. 5 ug of hST2-Fc (or control Fc protein), 2 ug of hIL-33-His (or control His protein), and protein G resin (or anti-His resin) were incubated in 0.5ml RIPA buffer overnight at 4 degrees C. The precipitates were separated by SDS-PAGE, electro-transferred onto NC membrane, and immunoblotted for the presence of hIL-33-His or hST2-Fc with anti-His HRP or anti-hIgG HRP, respectively.