Proliferation of FDC-P1 cells expressing either IL-3Rα + hβc (○) or IL-3RΔCT + hβc (□) in response to hIL-3 (A) or, as a control for viability, mGM-CSF (B). Proliferation was determined using the CellTiter 96 nonradioactive assay (Promega). Data are the means of triplicate points ± standard deviation (SD).