Affinity cross-linking of IL-4R in transfected CHO-K1 cells. Two micrograms of cDNA for IL-4Rβ (lanes 1, 2, and 3), IL-4Rβ plus IL-13Rα′ (lanes 4, 5, and 6), IL-4Rβ plus IL-2Rγ_c (lanes 7, 8, and 9), and all three chains (α′, β, and γ_c; lanes 10, 11, and 12) were transfected to CHO-K1 cells. Transfected cells (5 × 10⁶) were incubated with ¹²⁵I–IL-4 in the absence (lanes 1, 4, 7, and 10) or presence of excess unlabeled IL-4 (lanes 2, 5, 8, and 11) or IL-13 (lanes 3, 6, 9, and 12) for 2 hours at 4°C. Bound¹²⁵I–IL-4 was cross-linked to IL-4R with (DSS). The cells were then lysed at 4°C with modified RIPA buffer. The resulting lysate was analyzed by electrophoresis through an SDS-PAGE (7%) gel. The gel was dried and exposed to radiograph film for 4 days at −80°C. The molecular weight markers are shown on the left. The positions of different receptor chains are indicated (IL-4Rβ, black arrow; IL-13Rα′, white arrowhead; IL-2Rγ_c, black arrowhead; and approximately 55 kD, white arrow).