Surface expression of the human GM-CSF receptor subunits in transduced CTL-EN cells. CTL-EN cell lines expressing GMRαβ_c (A), GMRαβ_cSer585Gly (B), GMRαβ_cTyr577Phe (C), or GMRαβ_cF8 (D) were stained for the α subunit (GMRα) with the 4H1 monoclonal antibody (thick line) and the β_c subunit using the 1C1 monoclonal antibody (filled) as described in “Materials and methods.” As a control, cells were also stained with an isotype-matched control antibody (thin line). Cells were then stained with antimouse PE-conjugated secondary antibodies and analyzed by flow cytometry.