Induction of heterodimerization of the cytoplasmic domains of β_IL3 and _IL3 is mitogenic in Ba/F3 cells. Flow cytometric analysis confirming expression of (A) the CD16/7 chimeric receptors. The bottom righthand panel represents the CD16 signal obtained in cells expressing both CD16/7/ and CD16/7/β. (B) The expression of CD16/7/ and CD8/β. Thin lines represent results with cells treated with FITC-coupled secondary antibody alone; thick lines represent results with cells treated with CD16 and FITC-coupled secondary antibody. (C and D) [³H]-thymidine incorporation of Ba/F3 cells transfected with the indicated CD16/7 chimeras in response to addition of the CD16 antibody, 3G8. Cells were cultured with increasing amounts of 3G8 for 40 hours and then incubated for an additional 8 hours in the presence of [³H]-thymidine. Data are plotted as the percent maximal [³H]-thymidine incorporation observed in IL-3.