Effect of β_c on the proliferative response of Ba/F3-EpoR to Epo. Tritiated thymidine incorporation assay of Ba/F3-EpoR+ β_c (•) or Ba/F3-EpoR (○) grown in various concentrations of Epo (A and B) or mIL-3 (C and D). (B and D), respectively, represent the data in (A and C) normalized to maximal proliferation. The upper panels show that cells transfected with β_c (•) have a greater sensitivity to Epo than cells that were not (○). The lower panels show that the dose response of the same cells to IL-3 was not affected.