(A) Flow cytometric profile of FDCP-mix hIL-3/GM R cells. Expression of the chimeric receptor was determined by flow cytometry by using an anti–hIL-3 R antibody as outlined in Fig 1. (B) Effects of hIL-3 on proliferation of FDCP-mix cells expressing (i) chimeric hIL-3/hGM R, (ii) hIL-3 R, and (iii) hGM R subunits. Proliferation was assessed by determining [³H] thymidine incorporation stimulated by hIL-3 and hGM-CSF (1 to 100 ng/mL) after 16 hours in culture. Cells were plated at 4 × 10⁵ per sample for the chimeric hIL-3/GM R cells and the hGM R cells. Results are expressed as percentage of control (10 ng/mL mIL-3) and are the mean values from at least 3 experiments ± SEM. Similar results were obtained for at least 3 clones of each transfect. (C) Effects of hIL-3 on morphology of FDCP-mix cells expressing (i) chimeric hIL-3/hGM R (ii) hIL-3 R, and (iii) hGM R subunits. Morphology was assessed with May-Grünwald/Giemsa cytospin preparations of cells cultured in either (i), (ii) 100 ng/mL hIL-3, or (iii) 100 ng/mL hGM-CSF for 7 days as appropriate; (i) hIL-3/GM R cells, (ii) hIL-3 R, and (iii) hGM R cells. Bar, 10 μm. Similar results were obtained for at least 3 clones of each transfect.