Flow cytometric analyses of expression of chimeric receptors. CTLL-2 cells expressing both β_IL-3 and _IL-3/β_IL-3 (top), or _IL-3and β_IL-3 (bottom) were stained with antibodies against the extracellular domain of _IL-3 or β_IL-3. Thin lines represent results with cells treated with fluorescein isothiocyanate (FITC)-coupled secondary antibody alone; thick lines represent results with cells incubated with anti-receptor antibodies and then FITC-coupled secondary antibody. CTLL-2 cells bearing _IL-3 alone or β_IL-3 alone displayed levels of expression similar to those shown for CTLL _IL-3 + β_IL-3.