¹²⁵I–IL-13 binding and cytotoxicity of IL-13 toxin to CHO-K1 cells transfected with IL-13Rα2 deletion mutants.

Schematic representation of the wild-type and mutant IL-13Rα2 chains. EC, extracellular domain; TM, transmembrane domain; IC, intracellular domain (A). cDNA for various mutant receptor chains (6 μg/chain) was transfected into cells (5 × 10⁵) by using GenePORTER reagent for 48 hours. For IL-13 binding assay, 5 × 10⁵cells were incubated with 200 pmol/L ¹²⁵I–IL-13 with or without a 200-fold molar excess of unlabeled IL-13. Binding assays were performed in 2 separate experiments. Cell-bound radioactivity was determined as described in “Materials and methods” (B). CHO-K1 cells were transfected with IL-13Rα2 and its mutants, and then IL13-PE38QQR cytotoxicity was determined by protein synthesis inhibition assay. The results are represented as means ± SD of quadruplicate determinations (C).