The cytoplasmic tyrosine residues of the human IL-7Rα are required for IL-7-dependent cell proliferation. (A) A schematic illustration of the human IL-7 receptor complex composed of the human IL-7Rα and the human γc. Y denotes the cytoplasmic tyrosine residues. (B) IL-7-induced proliferation of various cell lines as indicated was examined as described in Fig. 2B. 100 ng/ml IL-7 was used. (C) Surface expression of the wild type/mutated human IL-7Rα and human γc in the cell lines. Exponentially growing infected Ba/F3 cells were analyzed by flow cytometry for cell surface expression of human IL-7Rα and γc. (The growth of cells was examined in 3 independent sets of experiments and found to be similar. The results from one representative experiment are shown).